Physics/Radiopharm 2 Flashcards
1
Q
Define X, A, Z, and N on an illustration of an element
A
X = element symbol A = mass number o (vs. atomic mass = total mass of protons, neutrons and electrons in a single atom) Z = atomic number N = neutron number
2
Q
Name four primary forces that act on an atom.
A
o Electromagnetic force
o Weak force
o Strong force
o Gravity
3
Q
As atomic number increases why is there an excess of neutrons?
A
Neutrons/protons -> attractive residual strong nuclear force (act over very short distances)
Protons ->repulsive Coulombic forces (act over longer distances)
So, with ↑Z, ↑ N to counteract longer range Coulombic repulsion by protons
4
Q
Question on nucleons – what they are, what the differences are between them and what they are made of
A
Nucleons = particles making up atomic nucleus = protons and neutrons, consist of quarks bound by residual strong nuclear force, mediated by gluons
5
Q
Question on isotopes, isotomes, isobars, etc.
A
Nuclides with same: o isotopes – proton number o isobars – mass number o isomers – proton and neutron number, but different energy state o isotones – neutron number
6
Q
Define binding energy, do heavier elements have higher/lower BE, explain
A
Binding Energy (BE) = energy released by dissociating a system into constituent parts = (Σ (masses of individual components) – (mass of bound system)) c2
2 types of BE: atomic vs. nuclear, both ↑ with ↑A, due to ↑ constituent parts, therefore >energy released by dissociating
7
Q
For an endoergic nuclear reaction, what are the starting and threshold energies, and which of these two quantities is equivalent to the energy required to make it go? Define coulomb barrier.
A
Endoergic nuclear reaction: a reaction that requires energy to be injected in order to proceed.
Threshold energy = minimum kinetic energy of bombarding charged particle for nuclear reaction to be energetically possible
Starting energy = minimum kinetic energy of bombarding charged particle required to overcome the Coulomb barrier and to conserve momentum
Minimum kinetic energy for endoergic nuclear reaction is the larger of these two
Coulomb barrier: minimum energy to overcome repulsive electrostatic force between a bombarding charged particle and the target nucleus
8
Q
What is the relationship between energy and wavelength of a photon
A
Inverse relationship: E=hc/λ
9
Q
Question about the radioactivity of one Curie and what it initially represented, i.e. number of decays in a second for Radium-226.
A
1 Ci = 3.7 x 10^10 Bq = disintegration rate of 1 g of 226Ra
10
Q
Define gamma ray, line of stability.
A
Gamma ray: electromagnetic radiation released from nucleus during decay
Line of stability: (draw arrow to line of stability on graph) N:Z ratio where more stable nuclei tend to lie
11
Q
Question on types of decay for varying nuclides, i.e. proton rich or neutron rich, as well as stability of very small and very large nuclides.
A
proton rich: β+ decay, electron capture
neutron rich: β- decay, high Z: α decay and spontaneous fission
small nuclides stable if N:P ~ 1
large nuclides stable if N:P ~1.5
very large (Z > 82) all unstable (Bi-209 (Z=83) recently (2003) found to be unstable)
12
Q
Why does the number of neutrons in the nucleus have to increase relative to atomic number in order to maintain stability in larger nuclei?
A
Neutrons/protons -> attractive residual strong nuclear force (act over very short distances)
Protons ->repulsive Coulombic forces (act over longer distances)
So, with ↑Z, ↑ N to counteract longer range Coulombic repulsion by protons
13
Q
Why are atoms radioactive? What will make them stable?
A
Elements away from line of stability (i.e., N:Z = 1 for small nuclei and N:Z = 1.5 for large nuclei) tend to decay toward line of stability to become stable
Nuclear stability is determined by the nuclear shell structure. This depends on:
o Even numbers of nucleons (protons and neutrons) are more stable, while odd nucleon numbered nuclei tend to be less stable
o The ratio of protons to neutrons, which must decrease with increasing Z; those falling out of the range of stability, or which have too many protons and neutrons overall, are unstable and undergo radioactive decay, mediated by the weak nuclear force
14
Q
describe 4 particles from nuclear transformation and what’s average energy and soft tissue penetration?
A
γ from IT: discrete energy; highly penetrating
e- from β- decay: Eavg ~ 1/3 Eβmax, mm-cm penetration
Neutrino: residual energy from β+ decay, essentially infinite penetration
Antineutrino: residual energy from β- decay, essentially infinite penetration
Auger electrons: discrete energy (BEK – 2 BEL), typically nm-μm penetration
Characteristic X-ray: discrete energies usually <100 keV, low penetration due to low energy
15
Q
Given a beta minus decay scheme and asked to graph the energies of the beta particles and label. French: [Draw the energy distribution curve of a negatron emitted by beta minus decay. Label E-max, E-mean and both axes
A
n -> proton + electron + antineutrino
Also: AZX -> AZ+1X + antineutrino + energy
Decays to right
16
Q
What other “particle” carries away energy in Electron capture?
A
Positron
17
Q
Write the equation for positron decay for element with mass A and atomic # Z. If a particle undergoes positron decay, does it transmutate?
A
AZX -> AZ-1X + positron + neutrino + energy
Yes, transmutates
Transmutation happens when parent radionuclide (X) and daughter product (Y) are different chemical elements.
Transmutation: B-, EC, B+, alpha, only isomeric transition and internal conversion don’t
18
Q
what’s common between positron and EC in terms of decay and what factor favours EC?
A
Both in low N:P ratio nuclides, results in Z-1 transmutation and are isobaric
↑Z favours EC
In both positron forms a neutron, both isobaric decay with transmutation, one by the emission of positron and neutrino (positron decay), the other by capture of K-shell electron by the nucleus and subsequent X-ray or Auger emission (EC). Larger elements favour EC as the K-shell is closer to the nucleus and more easily captured.
19
Q
Two decay modes for a proton rich nucleus. What orbital process can occur after this? Emission that can accompany electron capture is?
A
Electron capture (EC) & positron decay
For EC, get hole in an inner electron orbital shell, results in emission of characteristic X-ray or Auger electron
20
Q
Does the emission from a proton-rich isotope lead to transmutation?
A
Yes, EC or positron decay, resulting in Z-1
21
Q
What type of radionuclides undergo decay by β+ and electron capture? What determines which decay the radionuclide undergoes? Why do heavier atoms undergo EC?
A
Low N:P ratio (proton rich) nuclei
If transition energy <1.022 MeV, can only have EC; must be >1.022 MeV, for positron decay; >transition energy makes positron more likely
↑ Z have inner shell electrons more tightly coupled to the nucleus ↑EC
Beta plus decay occurs in lighter elements, electron capture occurs in heavier elements.
22
Q
What’s Auger electron? Can you have Auger electron from K shell? Why?
A
Occurs when an inner shell vacancy filled by an outer shell electron
Energy released enough to eject an outer shell electron, the Auger electron, but not enough to eject an inner shell electron such as from the K shell
Hole in K shell filled by L shell electron
Energy released ejects another L shell electron = Auger
Eauger = K-2L
Emitted from outer shell, result of characteristic X-ray overcoming binding energy
KLL = k-shell absence filled by L-shell electron; energy released overcomes binding energy of another L-shell electron which is ejected as the Auger electron; any energy above this L-shell binding energy is conferred as kinetic energy
23
Q
Define Auger electron/effect, effect of Z on fluorescent yield. Can K shell electrons be ejected as Auger electrons? Why?
A
Occurs when an inner shell vacancy filled by an outer shell electron
Energy released enough to eject an outer shell electron, the Auger electron, but not enough to eject an inner shell electron such as from the K shell
Fluorescent yield = probability of characteristic x-ray / probability of Auger, ↑ with Z
24
Q
Questions about internal conversion vs. auger effect and associated energies of the two processes.
A
Internal conversion Auger
Energy source: Excited/metastable nucleus vs Orbital electron transition
Origin shell: Inner vs Outer
Kinetic energy: Discrete (Eγ – BE) vs Discrete (BEhole – BEtransition – BEAuger )
Auger effect – when an outer shell electron moves in to fill a vacant inner shell electron, the energy released is transferred to an orbital electron which is then emitted instead of characteristic x-ray.
Internal conversion – nucleus decays by transferring energy to an orbital electron, which is ejected instead of the gamma ray. The conversion electrons usually originate from one of the inner shells (K or L), provided the binding energy can be overcome. The orbital vacancy is filled by an outer shell electron, accompanied by emission of characteristic x-ray or Auger electron.
25
Name two differences between beta emission and internal conversion.
Beta vs IC
Origin of electron - Nuclear decay vs inner shell orbit
Kinetic energy - Spectrum vs discrete (Egamma - BE)
Nuclear transmutation - Yes vs No
Electric charge (+1 or -1) vs -1
Associated particle emission - neutrino/antineutrino vs none
The important differences are that:
o In beta decay, the electron originates from the nucleus while in internal conversion it originates from an electron shell.
o Beta particles are emitted with a continuous spectrum of energies, while conversion electrons have a discrete series of energies determined by differences of gamma ray energy and orbital electron binding energies.
26
Protons vs. neutrons vs. electrons
P vs N vs e
Composition: baryones containing quarks vs same vs leptons
Charge - +1, 0, -1
Mass - 1.007 amu vs 1.009 amu vs 0.0005 amu
Stability - Stable; unstable; stable
27
What is the use of bateman equation?
Solution of Bateman differential equations allows calculation of daughter radionuclide activity in a decay chain given starting conditions (e.g., for generators)
A set of first-order differential equations describing the time evolution of nuclide concentrations undergoing a serial or linear decay chain (simplest scenario is parent-daughter decay); the solution allows for determination of
daughter activity given starting conditions (i.e., initial parent and daughter atom number, activity or concentration)
28
repeat of secular and transient equilibrium and examples
Secular equilibrium – T1/2 of parent is >> daughter that decrease of parent activity is negligible over course of observation (>= 100x)
o Ra-226 (T1/2 = 1620 years) -> Rn-222 (4.8 days)
o Cs-137 (30 years) -> Ba-137m (2.6 min)
16
o Sn-113 (117 days) -> In-113m (100 min)
Transient equilibrium – T1/2 of parent is longer than daughter T1/2 but not “infinite” (10-50x) FIGURE 4-8
o Mo-99 (66 hr) -> Tc-99m (6 hr)
o Y-87 (80 hr) -> Sr-87m (2.83 hr)
No equilibrium – daughter T1/2 is longer than parent T1/2 FIGURE 4-9
o Te-131m (30 hr) -> I-131 (8 days)
29
Know examples of generator pairs for both secular and transient equilibrium and their associated half lives and decay schemes
and decay schemes.
Secular
o 82Sr /82Rb/82Kr: 25.4d (EC)/76s (EC/β+)
o 68Ge/68Ga/68Zn: 271d (EC)/68m (EC/β+)
o 81Rb/81mKr/81Kr : 4.6h (EC/β+)/13.1s (EC/IT)
Transient
o 99Mo/99mTc/99Tc: 66h (β-)/6h (IT/IC)
o 87Y/87mSr/87Sr: 80h (EC/β+)/2.8h (IT)
30
What is the ratio of moly and technetium at equilibrium
Ratio of activities, Ad(t)/Ap(t) = (Tp / Tp - Td) x B.R. = (66 / 66 - 6) x 87% = 0.957
31
How long does it take to obtain ½ the maximum yield of a Tc generator
Numerical solution in Mathematica yields
| o t½max = 4.47614 h
32
Define Carrier. Define Specific activity. Calculate the carrier-free specific activity for I-131
Carrier = stable isotope of the radionuclide within sample
Specific activity = ratio of the radioisotope activity to the total mass of the element present
Carrier-free specific activity (CFSA) radionuclide = The highest possible specific activity.
CFSA (Bq/g) = 4.8 x 10^18/(A x T1/2)
A= mass number, t1/2 = ½ life (days)
Shorter t1/2, higher the specific activity
I-131: 4.8 x 10^18 / (131x8) = 4.6 x 1015 Bq/g
Tc-99: 4.8 x 10^18 / (99x(6/24)) = 2.5 x 10^17 Bq/g
33
Specific activity of eluate after 24 hours (After 24 hours, what is the specific activity of 99m-Tc)
SEE NOTES
34
What are the physical half life and photon energy of I-123?
T1/2 = 13.2 h
| Eγ = 159 keV
35
Complete the Table below regarding: I-123 vs. I-131
131; Reactor; β-; 8 d; Eγ = 364 keV; Eβmax = 0.61MeV
Range in soft tissue 0.4mm
I-123; Cyclotron; electron capture; 13 h; Eγ = 159 keV
36
Question on radionuclides and half lives including, but not limited to, krypton-81m, I-123, Indium-111, strontium-82, cobalt-58, chromium-51 and other odd nuclides
```
81mKr - 13s
123I - 13.2h
111In - 67h
82Sr - 25.5d
51Cr - 28d
58Co - 71d
```
PLUS SEE NOTES
37
4 radionuclides for radioimmunotherapy. Rank in order of longest path length
90Y (2.3 MeV) > 131I (606 keV) > 177Lu (498 keV) > 111In (Auger)
** ALSO SEE EDMONTON REVIEW NOTES ***
38
Nuclides and T½ given, mix and match: Rb-82, Ga-68, Tc-99, O-15, Kr-81m
```
Rb-82 75s
Ga-68 68min
Tc-99 211,000 years
O-15 2min
Kr-81m 13s
```
39
What are the 2 energies of gamma from 57Co
T1/2 = 271 days, decays by EC
22 3 gamma energies:
o 122 keV (86%)
o 136 keV (11%)
o 14 keV (9%)
40
67Ga. What are the 4 peaks? (4 energies of 67-Ga ) Other radionuclide that decay by EC
93, 185, 300, 394 keV
Other EC decay?
o I-123, I-125, Ga-67, In-111, Tl-201, Xe-127, Fe-52, Se-75, Co-57, Co-58, Cr-51
o All the positron emitters
41
Order the path length for F-18, C-11, N-13, O-15 from shortest to longest
```
PET tracer (from shortest to longest path length)
F-18 (0.63 MeV) -> C-11 (0.96) -> N-13 (1.2) -> O-15 (1.7)
```
(Max energy)
42
Why do we prefer to use mean root squared as opposed to FWHM for describing positron movement
FWHM best for Gaussian functions
Positron range distributions have long-tails and are poorly described by Gaussian functions
Root-mean squared is better indicator of positron range effect on spatial resolution
43
What are two types of reaction to produce radionuclide in reactor?
what reaction is important to keep chain reaction going in the previous question?
Fission
Neutron activation
Fission (highly contaminated requiring meticulous methods of separation, high specific acitivity/NCA products, low yields)
Neutron capture (low specific activity, carrier added products, chemical separation not necessary unless impurities develop).
o 235U + n -> 236U*, the objective is to have each fission neutrons emitted from one fission event stimulate, on average on additional fission event. This is accomplished by moderators (Heavy water and graphite) that thermalize the ejected neutrons, and control rods (cadmium and boron) that absorb the neutrons
44
Energy is released by nuclear fission to produce radionuclides. What quantity? What is the substrate of this reaction? Write the reaction in question.
202.5 MeV into KE of fission products
235U + n 236U*
Fission of one atom of U-235 releases 202.5 MeV in kinetic energy of fission products.
45
Mo-99 is produced from fission in the ------ solution. What is the physical half life of Mo?
Hot nitric acid is used to dissolve the target assembly (consisting of an alloy of enriched U-235 with aluminum)
This forms a nitrate solution of uranium, molybdenum and other fission products
This is eluted through an alumina column to trap the molybdenum
46
On radionuclide production and examples of each. Name four or five
Nuclear fission - 99Mo, 133Xe, 131I
Neutron Activation - 99Mo, 131I, 90Y
Generator - 99mTc, 82Rb, 81mKr
Cyclotron - 18F, 11C, 15O
47
How do you produce 123I? What’s the target source? Compare the direct and indirect methods. What’s the advantage of indirect method?
```
Indirect
124Xe(p,2n) 123Cs -> 123Xe -> 123I (most common)
15-30 MeV
Contaminant free; High specific activity
Gas phase extraction
123Xe is expensive
```
```
Direct
123Te(p,n)123I (direct)
124Te(p,2n)123I (direct)
15-8 (123Te)
26-20 (124Te)
Contaminants = 124I > 125I
Mineral acid to extract
```
48
What are the advantage of indirect methods of I-123 production?
high specific activity
less contamination by other iodine radioisotopes such as 124I and 125I
49
What is the common pathway in indirect methods of I-123 production? What is the target?
123Xe is intermediate in all indirect methods
| Most common target: 124Xe
50
What are the parts in a medical cyclotron, how does a cyclotron work?
Particle accelerator consisting of:
o Vacuum assembly: prevents collisional losses of charged particles
o Ion source: produces charged particles to be accelerated
o Pair of hollow dee electrodes with gap: accelerates charged particles using alternating electric current
o Magnet: confines charged particles to spiral path
o Electrostatic deflector (positive ion) or foil extractor (negative ion): alters path of charged particles toward target
o Target: contains nuclei to be irradiated to produce transmutated products
Particles from the ion source are accelerated towards one of the dees by the electrical field generated by the applied AC voltage. In the presence of the magnetic field, they follow a circular path to the opposite side of the dee. The particles are accelerated across the gap because of direction change in AC voltage. They follow an outwardly spiraling path because of gain in energy and the beam of particles is extracted and directed onto an external target.
51
What are 5 advantages of self shielded cyclotrons over vault cyclotrons?
Smaller space requirement (less shielding required)
Lower cost of installation
Less radiation to surrounding structure
Lower cost of decommissioning
Easier access to target and cyclotron for maintenance
Disadvantages:
o Lower energy
o More difficult to access for service
52
List 4 advantages of negative ion over positive ion cyclotron designs.
High beam extraction efficiency
Requires less shielding
Allows multiple extraction sites & therefore more than one target can be simultaneously irradiated and different radionuclides can be prepared simultaneously
Easier to service
53
Multipart question on cyclotron vs. reactor produced radionuclides
Cyclotron:
Costs - Decreased up front capital, increased operating costs
Line of stability - Proton rich
Charge of bombarding particle - +/-
Purity - Increased specific activity; usually carrier free
Yield - Increased activity per mass of target; decreased total quantity produced
Reactor:
Costs - increased up front capital; lower operating
Line of stability - proton rich
Charge of bombarding particle - neutral
Purity - Fission & transmutative = increased specific activity; Non-transmutative = decreased specific activity
Yield - Opposite
54
Describe 2 methods of F-18 production, advantages/disadvantages and which is more common
Method 1: H218O (p,n)18F*(H218O)n -> anion exchange resin to reuse H2O18-> F18-
Advantages: Increased yield, no carrier added
Disadvantages: 18O expensive (not anymore); 18F- chemistry in water difficult; Cannot easily obtain F2 for electrophilic reactions
Method 2: 20Ne(d,α)18F* in passivated Ni target (NiF)
Advantages: Produces [18F]F2 for electrophilic reactions
Disadvantages: Decreased yield; usually carrier added
55
Most common reaction for 18F production via electrophilic substitution and write out reaction?
What particles bombard parent? I
Minimum energy and bombard for how long?
a) 20Ne(d,α) 18F* in passivated Ni target (NiF)
b) Deuterons bombarding 20Ne in a Nickel housing
c)
• Exoergic reaction (releases energy), so threshold energy = 0, and minimum energy is the starting energy = 2.7 MeV (starting energy required to overcome Coulombic barrier and conserve momentum)
• Bombardment typically 2h
56
Principles of generator design.
decay-growth relationship between a long-lived parent and its short-lived daughter radionuclide
chemical property of daughter must be different from parent so it can be easily separated
Ideal generator:
o simple, gives high yield of daughter nuclide repeatedly and reproducibily
o properly shielded to minimize radiation exposure
o sturdy and compact for shipping
o eluate should be free from parent and adsorbent material
o sterile and pyrogen free
57
What is the concept behind 99mTc being eluted from the Al2O3 column and not 99Mo?
Mo-99 adsorbed on the alumina column in the form NH4+MoO4-
when it undergoes beta decay, loses affinity for the column and is free to be eluted with 0.9% NaCl solution via ion exchange (a Cl- ion is exchanged for a TcO4-)
58
Eluate should be ____,____ and free of _____.
Clear, colorless, free of particles
59
Label schematic of Mo/99mTc generator
```
Critical components
o Eluting solvent/vial
o Glass column with alumina adsorbent containing MoO42-
o Filter
o Evaculated collecting vial
o Shielding
```
60
How many weeks after manufacture is Mo/Tc generator good? How long is the eluate good to use? Name 2 things to test the eluate for.
Generator: Lantheus Technelite expires 14 days post-manufacture
Eluate: 12h at room temperature
Tests:
o 99Mo breakthrough <0.15 kBq/MBq at time of administration (RN purity)
o Al3+ breakthrough <10 μg/ml (chemical purity)
61
How do you dispose of a molybtech generator. Give two ways.
Store and decay until activity below exemption quantity, then dispose in garbage (10 half lives - 660 hours)
Return to manufacturer or approved disposal facility
62
20 cc saline into generator and only 10 cc out, ?cause and what could you do to fix it. (20 ml put into a dry generator, and 10 come out. How can this affect this next elution? How can you prevent this problem?)
Most probable cause for decreased volume out is partial loss of vacuum in the vacuum vial used to draw eluant out
Can use a second vacuum vial
If no additional eluent can be withdrawn, consider a leak in the system (tubing, cracked column), which depending on design, may require return to manufacturer
Also, may have excessive ingrowth with excessive Tc-99 if don’t complete elution
63
How do you assess for aluminum content. Briefly describe. What is the limit?
Al3+ breakthrough: <10 μg/ml (chemical purity = fraction of material in desired chemical form, whether or not all of it is in the labeled form)
Testing methods: aurintricarboxylic acid colorimetric test paper or methyl orange
Presence: may indicate lack of stability of column and can affect radiopharmaceutical synthesis and biodistribution
o MDP: colloid formation; increased liver uptake
o Sulfur colloid: ↑ particle size
o RBC damage causing ↑ splenic uptake
o DTPA dissociation: increased free pertechnetate
64
What is radionuclide purity? How do you test for 99mTcO4- impurity?
Fraction of total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical
Assay in dose calibrator with and without shielded container to determine 99Mo activity
65
Define radionuclide purity. What is the limit for Mo-99 in Eluate? Name/ Describe two methods for testing for molybdenum contamination.
Fraction of total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical
99Mo limit in administered dose (at time of administration): <0.15 kBq/MBq
Two methods:
o Assay in dose calibrator with and without shielded container to determine 99Mo activity
o Colorimetric: phenylhydrazine added to eluate
66
Question on detection / how a moly shield works in detecting molybdium in a technetium element. Second part on alternative to detecting molybdinium in the element.
Moly shield absorbs low energy 140 keV photons from 99mTc, but allows most of 740 and 780 keV photons from 99Mo through
o 6mm leads allows 35% of 740 & 780 keV photons through, so x3.5 to get breakthrough value
Alternative: colorimetric test with phenylhydrazine
67
Define chemical purity, radiochemical purity, and radionuclide purity and give examples
Chemical purity: fraction of material in desired chemical form, whether or not all of it is in the labeled form
Impurities: Al3+, carrier I, trace metals in In labeling, Kryptofix, non-radioactive FDG
68
Define radiochemical purity. List 5 possible causes of radiochemical impurities in a pharmaceutical prep.
Radiochemical purity is the fraction of total radioactivity in the desired chemical form in the radiopharmaceutical. Impurities include free and hydrolyzed Tc-99m TcO4-
5 causes:
o Decomposition of the radiopharmaceutical due to the action of a solvent
o Changes in temperature or pH
o Light
o Presence of oxidizing or reducing agents
o Radiolysis
69
Define Rf: “relative front” or “retention factor”
Rf = ratio of distance traveled by component to distance traveled by solvent front
Retention factor, Rf, or relative front = ratio of the distance travelled by the component to the distance the solvent front has advanced from the original point of application of the test material. It is used to identify different components in a given sample.
70
What is the major problem with allowing a long time between elutions. Explain why this is an issue with certain preps and give two examples. How could you overcome this. (If generator not eluted a long time, how does this affect eluate? Which two kits are particularly affected and explain why.)
With a long time between elutions, have buildup of essentially stable 99Tc (carrier)
Competes with 99mTc in kits limited stannous, i.e., limited reducing agents
Obtain generator eluate with short in-growth time
o HMPAO & Ultratag RBC particularly effected
71
What are two generators other than strontium rubidium-82 and moly-99 technetium 99m?
68Ge (271 days) - 68Ga (68 min)
81Rb (4.6h) - 81mKr (13s)
72
5 generator parents name daughters Sn113, Ge68, Rb81, Sr82, Zn62
o 99Mo – 99mTc; 99Mo has t1/2 66 hr & decays by β- to 99mTc (87%) & 99Tc
o 113Sn – 113mIn; 113Sn has t1/2 115 days & decays by e capture to 113mIn
o 68Ge – 68Ga; 68Ge has t1/2 271 days & decays by e capture to 68Ga
o 82Sr – 82Rb; 82Sr has t1/2 25 days & decays by e capture to 82Rb
o 81Rb – 81mKr; 81Rb has t1/2 4.5 hr & decays to 81mKr
o 62Zn – 62Cu; 62Zn has t1/2 9.2 hr & decays by e capture to 62Cu
o Yttrium-87 – Strontium-87m
o Tellurium-132 – Iodine-132
73
Describe 2 generator systems commonly used for PET imaging currently in 2009, list half lives
o 82Sr/82Rb; 25 days/75 s
o 68Ge/68Ga; 271 days/68 min
74
Four methods of radiopharmaceutical labeling and give an example of each
Isotope Exchange - I-131-MIBG
Introduction of a Foreign Label - Tc-99m compounds; In-111 labeled cells
Bifunctional Chelates - In-111 DTPA albumin; Tc-99m antibody
Biosynthesis - Co-57 B12;
Recoil labeling - Iodinated compounds
Excitation labeling - 123I-labeled compounds (from 123Xe decay)
75
# Define and give two examples of each:
a) Fillers
b) Antioxidants
c) Reductants
d) Catalysts
A) Filler:
Used to achieve rapid solubilization & stable particle size during lyophilization, also gives radiopharmaceutical some bulk to make visible in vial
Mannitol (sestamibi kit)
NaCl (HMPAO kit)
B) Antioxidant:
o Prevents consumption of the reducing agent
Ascorbic acid
P-aminobenzoic acid (PABA)
C) Reductants
Reduces the TcO4 to a lower oxidation state, to make it more reactive
Tin: SnCl2, Sn-pyrophosphate, Sn-citrate, Sn-gluconate
Non-tin reducing agents (NaBH4 – sodium borohydride, HCl (hydrochloric acid), FeSO4)
```
D) Catalysts
Used to maximize reaction yield, but are not part of the final product
Kryptofix in FDG
Tartrate (MAG3 kit)
Citrate (MIBI kit)
```
76
What is the purpose of a buffer?
A buffer is used to dampen the change in pH following the addition of an acid or a base
It maintains the stability of the pH of the preparation
Examples: Na-citrate, Na-carbonate
77
Define “transchelation”. Name 2 tracers which are labeled by this method.
Transchelation = ligand exchange method
o Involves first forming a 99mTc-complex with a weak ligand in aqueous media and then allowing the complex to react with a second slowly reacting ligand that is relatively more stable
```
Tracers:
o 99mTc-MAG3 (through 99mTc-tartrate or 99mTc-gluconate)
42
o 99mTc-ECD (through EDTA)
o 99mTc-MIBI (through citrate)
```
78
Define chelation.
Chelation = The formation of coordinate covalent bonds between two or more separate binding sites within the same ligand and a single central atom
Examples:
o Tc-99m DTPA
o Tc-99m glucoheptonate
79
What is a bifunctional chelating agent?
Molecule that is conjugated to a macromolecule on one side and chelates a metal ion on the other
Modification of the functional group alters the biodistribution
80
What is a ligand?
Ligands possess an unshared pair of electrons that can be donated to a metal ion to form a complex
81
What is the most stable oxidation state of Tc and What is the most common tracer in this state?
7+ oxidation state
| TcO4- (also Tc-SC)
82
What are oxidation states of MIBI, DTPA, and pertechnetate?
Sestamibi 1+
DTPA 4+
Tc-99m TcO4- 7+
83
Oxidation state of SC, DTPA, MIBI?
7+; Pertecnetate and colloid
5+; citrate, gluconate, gluceptate, EDTA, MAG3, HSA, tetrofosmin, HMPAO
4+; HEDP (mixture of 3+ acid, 5+ basic, 4+ neutral), EDTA and DTPA (alkaline and neutral)
3+; DTPA and EDTA (acidic), DMSA, diphosphonates
1+; MIBI (1+) Coordination number of 6 net charge 1+
84
Which radiopharmaceuticals require heating?
1. MIBI
2. MAA
3. SC
4. ECD
5. MAG-3
6. Heat damaged RBCs
7. Technegas
8. Teboroxime
9. I123/I131 MIBG
10. 111IN-DTPA
11. FDG
12. FLT
13. I-131 Hippuran
85
What’s the limit of maximum size of MAA particles?
Maximum size is 150 μm
86
What component you have to add to make MAA besides reducing agent and buffer?
Human serum albumin
87
110 particles in 1x1 mm square on hemocytometer, how many particles / ml of MAA?
110 particles in 1 mm2, hemocytometers have a depth of 0.1 mm
therefore there are 110 particles in 0.1 mm3 or 0.1 μl, 1100 in 1 μl. There are 1000 μl per ml, therefor there are 1,100,000 particles/ml.
88
There was a question on differences between pertechnegas and technegas production.
Pertechnegas:
Production - >0.5% oxygen
Particle properties -> micro-aerosols of Tc oxides
Transit -> Rapid alveolar-capillary transit
Biological half life -> Short in lungs; behaves like TcO4
Technegas
Production - > pure argon atmosphere (< 0.1% oxygen)
Particle properties -> graphite enscapulated microparticles
Transit -> No significant alveolar-capillary transit
Biological half life -> Essentially infinite
Both formed by combusion of pertechnetate in furnace
89
Describe the method of pertechnegas production. How long until it must be used. What will happen if you wait longer. What should you check if there is thyroid/stomach uptake (2 things). (Technegas: 1) How made; 2) how long is dose good for prior to use; 3) what happens to a dose held too long?; 4) If thyroid and blood pool seen post pertechnegas, what TWO things to check?)
Load crucible with Tc-99m generator eluent (400-900 MBq in 0.14 ml normal saline)
To make Pertechnegas, require >0.5% oxygen
How long until it must be used
o For Technegas, as soon as possible, and certainly within the 10 minutes allowed
o For Pertechnegas, uncertain, but probably also <10 min
What will happen if you wait longer
o For Technegas, get aggregation into larger particles and migration to walls of the chamber
o In contact with water vapour, Technetium oxides in Pertechnegas hydrolise back to pertechnetate
What should you check if there is thyroid/stomach uptake (2 things)
o Impurity of Argon gas (99.99%) and introduction of oxygen
o Make sure correct eluate and have not over-filled crucible
90
Name 2 contents of DTPA kit. Once Tc04 added, what are the relative proportions of these 3. Why is this important?
DTPA and stannous chloride
10^5-10^8 mol DTPA:10^3-10^6 mol Sn2+ : 1 mol 99mTc
o Need enough Sn2+ to reduce all 99mTc
o Need greater amount of chelate to drive chemical equilibrium to form chelated complexes, and prevent Sn and Tc colloid formation
91
In kit preps, why is it important to keep O2 out of your vial.
O2 oxidizes Sn2+ (less Sn2+ available to reduce Tc) -> increases free pertechnetate
Increases radiolysis -> leads to free radicals that in turn produce free Tc99m-O4
92
What solvent to use for evaluating radionuclidic purity of In-111-DPTA-pentreotide
Methanol to elute product
Water to elute free In3+
93
Regarding WBC labelling, what needs to be in acidic environment and what pH?
111In-chloride (pH 5 in acetate buffer) to avoid In hydroxide formation
94
What are the uses of thiosulfate, gelatin, EDTA in SC kit?
Thiosulfate: source of S
Gelatin: maintains zeta-potential preventing aggregation
EDTA: chelates cations (e.g., Al3+) to prevent flocculation
95
Question on the size of filter to use for sulphur colloid in melanoma lymphoscintigraphy
0.1-0.2 μm
96
Question on particle sizes for various colloids or uses of colloids in clinical nuclear medicine. Particle size for lymphoscintigraphy, particle size for lung scan and particle size for sulphur colloid study.
Lymphoscintigraphy (filtered SC): 0.1-0.2 um
Sulfur colloid study: 0.1-1 μm
Lung scan/MAA: 10-100 μm
Technegas - 0.05-0.15 um
97
Name 3 biological tests performed on radiopharmaceuticals.
1. Sterility: absence of any viable bacteria or microorganism
2. Apyrogenicity: USP Rabbit test, limulus amebocyte lysate (LAL) test
3. Toxicity
98
How do you ensure sterility of radiopharmaceuticals?
Use sterile technique in preparation
Filter sterilize
Autoclave heat stable radiopharmaceuticals
99
Define pyrogenicity and two tests that are used to test for this. What is the most common cause of pyrogenicity in nuclear medicine radiopharmaceuticals?
Pyrogenicity: ability of substance to induce fever
Rabbit test and limulus amebocyte lysate test
Most common: bacterial endotoxins
rabbit test - inject 3 rabbits, if 1 temp increases > 0.6 degrees or total > 1.4 degrees then inject 5 more; if more than 3 greater than 0.6 degrees or total > 2.6 then the test is positive
100
How do you interpret the first part of the USP rabbit test for pyrogenicity.
First test:
o 3 mature normal rabbits weighing ≥ 1.5 kg are kept in a room with uniform temperature.
o A test sample is injected into the ear vein of each rabbit. The volume of the test sample must be an equivalent human dosage, on a weight basis, and often 3-10 times the human dosage by volume.
o The rectal temperature of each rabbit is measured at 1, 2 and 3 hours after injection.
o If the rise in temperature of each individual animal is less than 0.6oC AND if the sum of the temperature rises in all three animals does not exceed 1.4oC then the test sample is apyrogenic.
Second test:
Second test (if first test abnormal):
o Repeat initial study with 5 more mature normal rabbits.
o If not more than 3 of the total of 8 rabbits show a temperature rise of 0.6oC or more individually and if the sum or the individual temperature rises does not exceed 3.7oC, the material is considered to be pyrogen free.
101
What is a pyrogen? Modern method for detecting pyrogens, advantages over rabbit test. (What is the current standard test? Why is this preferred over the rabbit rest? Three reasons
Pyrogen: substance that can induce a fever when injected (i.e., systemic inflammatory response)
Limulus amebocyte lysate test
o No live animal testing
o Rapid result (1 hour)
o Less radiopharmaceutical needed
102
Describe 2 ways to sterilize a radiopharmaceutical
Autoclave
Filter sterilize (0.2 μm filter)
Irradiation
103
Kits with highest incidence of adverse reactions.
Historically: Tc-99m albumin microspheres
Current kit: highest is Tc-99m sulfur colloid (25%)
MDP (10%)
Also HIDA
104
Reaction involved in most common method of FDG production. What is the typical yield? What is the minimal radiochemical purity allowed?
Nucleophilic substitution in acetonitrile with Kryptofix as a phase transfer catalyst
Mannose triflate in acetonitrile added to Kryptofix 2.2.218F-
Acid hydrolyzed to 18F-FDG
Typical yield: 60%
Minimum radiochemical purity: 90%
105
Most common production method of 18 FDG and what is its’ target? French: [36. What is the minimum energy required for F-18 production?
18O(p,n)18F
| Target: 18O-H2O (minimum energy 2.6 MeV)
106
a) How do you produce 18F?
b) What is the FDG yield?
c) How do you check F-18 FDG for radiochemical purity?
d) What limit is allowed for radiochemical purity?
18O(p,n)18F (heavy water target, 10-18 MeV proton bombardment)
o 18F recovered as 18F-NaF by passing the irradiated water through anion exchange resin (QMA) column
o 18F- retained on column, eluted with potassium carbonate and Kryptofix 2.2.2 in acetonitrile
Nucleophilic substitution in acetonitrile with Kryptofix as a phase transfer catalyst (85°C 5 min)
o Mannose triflate in acetonitrile added to Kryptofix 2.2.218F-, with K2CO3
o 18F- attacks #2 C position on mannopyranose ring, displacing highly electronegative triflate group
Then acid or base hydrolysis
Acid or base hydrolyzed to 18F-FDG by removing acetyl protecting groups
Typical yield: 60%
Preparation time: 50 min
Final solution is filtered through 0.2 μm filter and diluted with saline as needed
Minimum radiochemical purity: 90%
QC
o Visual inspection
Clear, colorless solution free of particles, pH (4.5-7.5) – test with pH paper
o Specific activity >1 Ci/μmol (no special test, as 18F is carrier free)
```
o Radionuclide purity
Must be >99.5%
Use dose calibrator and do decay analysis
Acceptable t ½ = 109.7 min (105-155)
Or by gamma ray spectroscopy
```
o Radiochemical purity
Use silica gel 60 TLC plates developed in acetonitrile/water (95:5)
Must be >90%
18F-FDG (Rf=0.4)
18F-F- (Rf=0.1)
18F-FDG non-hydrolyzed intermediate (Rf=0.6)
o Chemical purity
Kryptofix 2.2.2: use color spot test that takes 5 min using pretreated strips of plastic based silica gel. Limit <50 μg/ml of sample volume
Acetonitrile, ethanol and 2-chloro-2-deoxy-D-glucose can be determined by gas chromatography
OR:
F-18 is produced by irradiation of O-18 water with protons in a cyclotron and recovered as F-18 sodium fluoride by passing the irradiated water target mixture through a carbonate type anion exchange resin column. Water passes through, but F18-(-) is retained on the column.
O-18(p,n) F-18 reaction
Yield is 6.5 Ci, <1.0 Ci for the Ne method.
Deoxyglucose is labeled with F-18 by nucleophilic displacement reaction of an acetylated sugar derivative (mannose triflate) followed by hydrolysis. The yield can be as high as 60%. This is highly dependant on the kit used.
107
List 2 FDG chemical impurities (worded as 2 NON radioactive contamination)
Acetonitrile
Kryptofix 2.2.2
FDG
Chemical purity:
o Kryptofix 2.2.2: use color spot test that takes 5 min using pretreated strips of plastic based silica gel. Limit is < 50 μg/ml of sample volume.
o Acetonitrile, ethanol and 2-chloro-2-deoxy-D-glucose can be determined by gas chromatography
108
What is the effect of radioactive decay on chemical reactions
Radionuclide-related
o Transmutation of radionuclide in decay alters chemistry
o Long-lived isomeric decay daughter may compete for labeling (e.g., Tc-99)
o High energy recoil or daughter radionuclides can participate in labeling reactions
Radiation-related
o Radiolysis may be:
Direct with high LET radiation like alpha paraticles, causing e.g., degradation of kit constituents
Indirect with low LET radiation, causing free radical production, that can interfere with labeling
o Autoradiolysis or indirect radiolysis can disrupt product as well
109
Methods of Radioiodination
```
o Triiodide method
o Iodine monochloride method
o Chloramine-T method
o Electrolytic method
o Enzymatic method
o Conjugation method
o Demetallation method
o Iodogen method
o Iodo-bead method
```
110
What is the dominant interaction of energy with matter at nuclear medicine energies?
For photons cross-over energy between photoelectric and Compton interactions are:
o Soft tissue/water: 20-30 keV
o NaI(Tl): 200-300 keV
o Pb: ~500 keV
Therefore, at Nuc Med energies of 100-200 keV, Compton dominates in soft tissues; photoelectric for NaI scintillators; photoelectric with high Z materials like Pb
111
Describe photelectric effect
Atom absorbs all energy of incident photon and an orbital electron is ejected. This electron is called photoelectron and KE = E(incident photon) – BE of photoelectron
112
Describe Compton scattering
Incident photon has much higher E than BE of electron it collides with so photon loses part of energy and is deflected through a scattering angle. Part of E is transferred to the recoil electron
E (scatter photon) = E0 / [1 + (E0/0.511) (1-cos Ѳ)], max when Ѳ = 0
E (recoil electron) = E0 – E (scatter photon), max when Ѳ = 180
113
Describe pair production
a photon interacts with the electric field of a charged particle, producing a positive-negative electron pair and the photon disappears.
KE of the electron pair = K0 – 1.022 MeV
114
Describe Coherent (Rayleigh) scattering
photon is deflected with essentially no loss of energy. Only important at relatively low energies (<= 50 keV)
115
At what angle of Compton scatter would the scattered photons be within 20% symmetric window?
Eγs = Eγ / (1 + (Eγ/511 keV) (1 - cos θ))
For Eγ = 140 keV photon, scattered photons are lower energy, so assuming 10% reduction in energy, Eγs = 140 – (10% x 140) = 126 keV yields 53.5°
116
Does the increase of the interaction media’s atomic number, Z, affect energy of Compton scatter photon?
No, Z does not affect Eγs
Eγs = Eγ / (1 + (Eγ/511 keV) (1 - cos θ))
No, Compton involves outer shell electrons
Generally independent of Z, proportional to 1/E
117
A small chart on the three mechanisms of question #30 with secondary photon and secondary electron, and you were to fill in the boxes for all three.
Photoelectric:
Secondary photon = characteristic xray
Secondary electron = photoelectrons (inner shell); Auger electron
Compton scattering
Secondary photon = Scattered photon (outer shell)
Secondary electron = recoil electron
Pair production
Secondary photon = annihilation photons
Secondary electron = positive/negative electron pair
118
What is minimum energy for pair production?
1.022 MeV
119
Describe 3 common interactions in NaI detector crystal
Photoelectric effect <250 keV
Compton >250 keV
Pair production >1.022 MeV
120
There is increased ionization density of charged particle at the end it track length. What is it called?
Bragg peak
121
Question on fluorescent iodes and what affects it.
o Fluorescent yield is the probability that the transition of an orbital electron from an outer shell into an inner shell vacancy will yield characteristic x-rays instead of Auger electrons.
o Fluorescent yield increases with increasing Z. In other words, heavy elements have a higher fluorescent yield because they are more likely to emit x-rays
122
Bremstrahlung: define. How can you shield most effectively?
Electromagnetic radiation produced by deceleration or altering direction of charged particles
Use low Z material to slow charged particles with minimal Brehmstrahlung production
123
Particulate radiation versus electromagnetic radiation - their differences and interactions with matter and give two examples.
Particulate interactions – (collisional) ionization, excitation (radiative) bremsstrahlung
EM interactions - photoelectric, Compton scatter, pair production, rayleigh coherent scatter.
124
Photon vs particulate radiation
```
Photon
Mass = 0
Charge = 0
Velocity = c
Ionization = indirectly ionizing
Interactions = photoelectric, etc...
```
```
Particulate radiation
Mass = +
Charge = possible
Velocity = < c
Ionization = directly ionizing
Interactions
-> if charged particle: Collisional losses (ionization, excitation); Bremsstrahlung
-> if neutral particles: elastic and non-elastic collisions
```
125
Name three interactions of particulate radiation with matter.
Ionization (collisional)
Excitation (collisional)
Bremsstrahlung (radiative)
126
Question on what type of ionization neutrons perform in matter. Second part of the question was what are the effects of indirect ionization? (Another recall: How does neutron react with matter?
Neutrons are indirectly ionizing, losing energy by collisions that produce secondary electrons (which in turn directly ionize)
When sufficiently slowed, can be captured (neutron activation)
127
Describe what happens with charged particle and matter “collision”?
Collision can result in ionization (when orbital electron is lost) or excitation (when an atom enters excited state)
Collisional interactions include ionization and excitation; charged particle passes close enough to exert an electrical force on the orbital electrons, if the force is strong enough the orbital electron will be removed and an ionization occurs, if not then excitation may occur and the energy can be dissipated in a number of ways (atomic emissions of IR, UV, visible radiation etc.)
128
what is delta ray?
An ejected electron that is energetic enough to cause secondary ionizations on its own.
129
Define Bragg Peak, Cerenkov Effect and LET
Bragg Peak – increase in ionization density from a charged particle near the end of its track length
Cerenkov effect – electromagnetic radiation emitted when a charged particle travels faster than the speed of light in a medium
Linear energy transfer (LET) – rate of energy transferred per unit track length
130
Define the inverse Square Law. If you triple the distance, the exposure is reduced by?
Inverse square law = as distance increases, the flux of radiation decreases as 1/r^2
So triple the distance, 1/9 the exposure
131
HVL for Tc-99m, Ga-67, Co-60 (another recall: HVL in lead)
99mTc: 0.03 cm
67Ga: 0.07 cm
60Co: 1.6 cm
HVL in lead:
1 mm tenth value layer for Tc-99m
132
What is soft tissue penetration for F-18 and C-11?
Maximum positron range: 18F 2 mm, 11C 4 mm
133
Three types of gas filled detectors.
Dose calibrator
Geiger-Muller counter
Survey meter
134
Name two ionization chambers used clinically
Dose calibrator
Geiger-Muller counter
Ionization chambers are quite inefficient for detection of x- and gamma- rays. Only < 1% actually interact with and cause ionization of gas molecules
135
Ionization chamber vs GM counter?? (isn't GM counter an ionization chamber?
```
Ionization chamber:
Voltage - 50-300
Discriminate individual events - N
Energy discrimination - N
Efficiency for detection of
γ & x-rays - Poor
Measure - Exposure rate (mR/hr or Gy/hr)
Quenching - N
Amplification - N
```
```
GM counter:
Voltage - 800-1000
Discriminate individual events - Y
Energy discrimination - N
Efficiency for detection of
γ & x-rays - Poor but better by factor of 10
Measure - Exposure rate (mR/hr)
Quenching - Y
Amplification - Y
```
GM more sensitive than ionization chamber types because they respond to individual ionizing radiation events
o display event counting rates (cpm)
136
Quality control of dose calibrator including testing frequency and deviation limit
o Constancy: The activity of a known amount of a long lived source should be checked daily and the measured value and decay corrected calculated value should not vary by >10%
o Linearity: ensures that the dose calibrator can indicate the correct activity over the range of use between 10 mCi to the highest dose that will be administered. Performed on installation and quarterly. Values should not deviate more than 10%
o Accuracy: The activity of a known amount of a calibrated source is measured and the measured value should be within 10% of the calibrated value. Performed on installation and yearly
o Geometry Dependence: ensures that the indicated activity does not change with volume or configuration. Usually perfomed by the manufacturer.
137
Name 2 ways to check dose calibrator linearity
1. Decay method (large dose of 99mTc measure decay every 6 hours over 72 hours, point on the graph that deviated most from the line <10%)
2. Sheilding method (series of lead shield, various thickness, apply correction and average, the result that deviates the most must deviate <10%)
138
3 Daily QC on Survey Meter
Battery check
Background
Constancy
performed daily to assess the sensitivity and consistency of the meter.
Probe is placed directly over a sealed source (eg. 226Ra or 137Cs) to measure the exposure. This exposure reading is compared with the annual calibrated source reading (should be within 10%).
139
Draw schematic of Geiger-Muller counter, describing function
High sensitivity counting-type ionizing radiation detector
Ionizations in gas chamber (argon + quenching gas) result in avalanches due to high voltage operation (accelerated electrons excited gas molecules UV photonsmore ionizations)
140
Label the parts of a GM counter
```
Input window
Gas/ionization chamber with cathode and anode
o Fill gas: argon + quenching gas
High voltage source
Counting circuitry
```
SEE NOTES
141
Characteristics of “quenching gas”
Ionized quenching gas can recombine with electrons without giving off UV radiation (by dissociating into molecular fragments)
Absorb UV radiation inhibiting further ionization
Electron donor
Used in the gas chamber of Geiger-Muller counters
142
What is TLD? What is the mechanism of TLD? What’s the range of TLD?
TLD = thermoluminescence device, a type of dosimeter
Radiation crystal excites electrons into long-lived trap states
Heating drops electrons from trap state to ground state produces detectable visible photons
Range: 0.05 mSv-10 Sv
Most common material: LiF
143
Describe OSL?
optically stimulated luminescence (OSL) aluminum oxide (most common), quartz, feldspar, and irradiation produces valence electron ionization and electron/hole pair formation, the electron get trapped between the valence and conduction bands, irradiation causes excitation into the conduction band and the electron can that relax and recombine with the hole via fluoresence). Single site vs. multiple site read. OSL can differentiate dynamic (normal) vs. static (contamination of the detector) exposure.
144
What are 4 advantages of NaI detectors? What are 2 disadvantages of NaI detectors?
Advantages:
o Good stopping power for 50-250 keV photons (photoelectric absorption)
o Efficient scintillator (1 visible photon/30 eV absorbed)
o Transparent to own scintillations
o Relatively inexpensive
Disadvantages
o Fragile
o Hygroscopic
o Higher γ energies Compton interaction dominates, requiring thicker crystal
145
Compare NaI, BGO and LSO for their photon yield, density, atomic number and hygroscopic property
Photon yield: NaI > LSO > GSO > BGO
Density: LSO > BGO > GSO > NaI
Zeff: BGO > LSO > GSO > NaI
Hygroscopic: NaI yes, others no
146
Name four crystals that are commercially available PET detector materials and rank them according to the following: density, light output and annihilation photon attenuation.
Density: LSO, BGO, GSO, BaF2, NaI
Light output: NaI, LSO, GSO, BGO, BaF2
Photon Attenuation: BGO, LSO, GSO, BaF2, NaI
Decay Constant: BaF2 (shortest), LSO, GSO, NaI, BGO
147
How does the decay constant affect PET performance?
Decreased randoms: can shorten coincidence timing window
TOF imaging: higher SNR
Decreased dead time losses: for high count rate studies
148
Properties of PET crystals:
given list of BGO, LSO, NaI, CsF, and BaF2
asked which has highest light output, highest density, which is BEST for PET
Light output: NaI
Highest density: LSO
LSO is best for PET
149
Of 5 given PET scintillator materials (LSO, BGO, GSO, NaI, BaF2), which is the best for each of the following properties: effective z, density, stopping power, decay time, light output.
```
Effective Z: BGO
Density: LSO
Stopping power: BGO
Decay time: BaF2
Light output: NaI
```
150
Name 3 properties of detector crystal and rank them for NaI
One of highest light output crystals
Good stopping power for 50-250 keV, but poor compared to other PET crystals
Inexpensive
151
Which crystal is radioactive in PET (autoscintillation)? What is the nuclide? Is this important? Why or why not? (Lu-176)
LSO, LYSO: 176Lu
| Theoretically autoscintillations can increase background
152
Name the components of a photomultiplier tube
photocathode – converts light photons into electrons
focusing grid that directs the photoelectron to the dynode
dynode – maintained at positive charge and attracts photoelectrons, producing many secondary electrons, which in turn are attracted to the next dynode, producing a large amount of current due to the electron multiplication factor
anode – collects shower of electrons to produce the current
glass housing to protect inside components and preserve vacuum inside tube
stable high voltage supply
153
Define detector efficiency? (I think they meant detection efficiency?) Describe each component of geometric efficiency equation?
D = g x e x f x F
Detection efficiency = efficiency with which a radiation measuring instrument converts emissions from a radiation source into useful signals from the detector
Geometric efficiency = efficiency with which the detector intercepts radiation emitted from the source, determined by detector size and distance from source to detector
Intrinsic efficiency = efficiency with which the detector absorbs incident radiation and converts them into potentially usable detector output signal, depends on detector thickness, composition, type and energy of radiation
f = fraction of output signals within PHA window
F = factor for absorption/scatter occurring within source or between source and detector
154
List 4 parts of a liquid scintillation counter system
Tube holder
Scintillation fluid
PMT
Counting and energy discrimination electronics
155
List 4 things in a liquid scintillation vial and explain briefly
Liquid scintillation counter is used to count B emitters such as H-3 and C-14 which would be absorbed in the glass or plastic of test tube used in a well counter. Also used to count low energy x- & gamma rays not detected efficiently by NaI detectors.
organic solvent – dissolves scintillator material and radioactive sample; absorbs most radiation from sample and transfer energy to scintillator molecules
primary solute (or fluor) – absorbs energy from solvent and emits light
secondary solute (waveshifter) – absorb emissions from primary solute and re-emit photons of longer wavelength which are better matched to PMT response
additives – improve some aspect of LS performance, eg energy transfer efficiency from solvent to primary solute
156
Three approaches to quench correction for liquid scintillation counting?
Internal standardization method
o Count twice, with and without added standard
Channel ratio method
o Count once, in 1 channel to be unquenched, channel 2 is quenched
Automatic external standardization method
o Unshielding/shielding of an external standard source
157
Name 3 reasons why semiconductor gamma cameras have not been produced until now.
The 3 reasons have to do with the advent of CZT
o 1.Previously semiconductor crystals required storing (because of condensation of Li) and operation (thermal current=noise) at very low temperatures (liquid N2)
o 2.Only very thin (max 1cm) detectors could be produced because of the difficulty in avoiding impurities (HPGe), and this process was extremely expensive.
o 3.Very expensive because of these.
o 4.CZT is also denser than the other two.
Advantages:
o more efficient absorber of radiation
o larger electrical output signal per unit of radiation absorbed
o can do energy-selective radiation counting
158
Give energy resolution in %FWMH for NaI and CZT/CdTe?
Varies depending on experimental setup: typically ~13% for NaI and 3-4% for CZT
159
what’s the significance of good energy resolution
Accurate spectroscopy
| Can narrow acceptance window to reject scatter
160
You want a CZT, list 4 reasons you can provide to hospital board to convince them to buy it?
↓ imaging time for same quality of images
Can ↓ patient dose while maintaining same diagnostic quality
Higher spatial resolution (ability to separate normal from abnormal activity)
Better quality images for obese patients due to improved energy resolution and scatter rejection
161
What are the components of a well counter? What is a well counter used for? What are advantages and disadvantages of a well counter compared with a dose calibrator? liquid scintillation counter?
```
Components
o Well within a detector crystal
o PMT
o Shielding
o Counting circuitry
```
```
Used for highly sensitive energy-selective counting
o Radioimmunoassays
o Radioactivity in blood/urine samples
o Radiochemical assays
o Radiopharmaceutical quality control
o Wipe tests
```
Advantages/Disadvantages
o More sensitive than dose calibrator
o Paralyzable; susceptible to dead time losses
162
The patient is given 2 mGy of α tracer and 2 mGy of β tracer, what is the dose equivalent?
wR = 20 for α, 1 for β, so:
α ~40 mSv, β ~ 2 mSv.
```
Weighting factors :
x-rays; gamma; electrons; positrons; muons = 1
neutrons: < 10keV = 5
10-100 keV = 10
100 keV-2MeV = 20
2 MeV-20MeV = 10
> 20 MeV = 5
protons = 2 (if > 2MeV)
alpha particles; fission fragments; heavy nuclii = 20
```
163
Define effective dose, equivalent dose
H = absorbed dose
Equivalent dose = H x wR
o wR = radiation weighting factor
Effective dose = H x wR x wT
o wT = tissue weighting factor
Equivalent dose: absorbed dose modified to take into account the different biological damage produced by certain types of radiation:
Effective dose: absorbed dose from a specific type of radiation modified to take into account different organ radiosensitivity:
164
Define stochastic effect and deterministic effect and give an example of each
Stochastic effect: radiobiologic effect where probability of occurrence ↑ with radiation dose, but severity independent of dose; no threshold dose
o Example: cancer
Deterministic effect: radiobiologic effect with a threshold dose; severity ↑ with radiation dose
o Example: cataract
o Examples: myelosuppression, skin erythema, cataracts (200 rad), temporary male sterility (15-30 rad), permanent male sterility (400-600 rad)
165
Define stochastic effect, deterministic effect. Give 2 examples of each. Which one is ALARA trying to prevent?
• Stochastic effect: radiobiologic effect where probability of occurrence ↑ with radiation dose, but severity independent of dose; no threshold dose
o Example: cancer and heritable mutations
• Deterministic effect: radiobiologic effect with a threshold dose; severity ↑ with radiation dose
o Example: cataract and skin erythema
• ALARA -> stochastic effects
166
List in order of sensitivity various tissues. The ones listed were skin, gonads, bladder and lungs. But you may need to know other ones. There was hepatocytes, muscle cells and neuro tissue.
Sensitivity refers to deterministic effects, which are not exactly equivalent to tissue weighting factors
Testes > Bone marrow aplasia > Ovaries > Lung > Liver > Brain > Skin > Muscle (adult) > Bladder
PLUS SEE PAGE 94 OLD DOC
167
Define weighting factor. Which 2 organs have the highest weighting factor?
Tissue weighting factor: ratio of stochastic risk from irradiation of a specific tissue compared with the risk when the whole body is irradiated
ICRP 103: breast, RBM, lungs, colon, stomach (0.12), gonad (0.08 only)
168
Relative radiosensitivies of different cell types?
Very high = lymphocytes; immature hematopoetic cells; spermatagonia
High = urinary bladder epithelium; gastric mucosa
Intermediate = liver, pancreas, thyroid, nerve cells
Low = muscle cells; connective tissue; bone and cartilage
169
Basis of MIRD calculations
MIRD method, aka absorbed fraction method, allows calculation of radiation dose delivered to a target organ from radioactivity contained in one or more source organs in the body.
amount of activity and time spent by the radioactivity in the source organ are determined
total amount of radiation energy emitted by the radioactivity in the source organ is calculated.
fraction of energy emitted by the source organ that is absorbed by the target organ is determined.
170
What is reciprocal theory in dosimetry calculation?
The theory states that for a specific organ pair, the specific absorbed fraction is the same, regardless of which organ is the target and which is the source.
171
Factors that determine radiation exposure:
```
Extrinsic:
o Type of radiation
o Time
o Distance
o Shielding
```
Internal:
1) Total amount of activity and T1/2 effective of the radionuclide in the source organ
2) Amount of radiation energy emitted per activity
3) Fraction of radiation energy emitted that is absorbed by any target organ.
172
Dose to gonads after 131I-iodide therapy?
For 5.5 GBq dose (150 mCi) = 0.141 Gy testes; 0.208 Gy for ovaries
173
Effective dose of various radiopharmaceuticals:
Effective dose in mSv/MBq
I131 >> InWBC > Thallium > I131MIBG
174
What is free radical? What does it do?
An atom, molecule or ion with unpaired electrons or in an open shell configuration, which tend to be highly chemically reactive, and typically have a half-life 10^-10 to 10^-5
Can cause breakage of bonds, such as in the DNA backbone
175
Three features of a free radical.
free (unbound) atom or molecule
unpaired electron in outer shell
highly reactive - short lifetime
176
Define direct and indirect action of radiation. Which one causes damage that is easier to repair?
Direct action: radiation (typically high LET) interaction with DNA
Indirect action: radiation (typically low LET) interaction with other molecules, producing free radicals, that cause DNA damage
Indirect generally easier to repair, as usually constitutes single strand breaks, while direct is more likely to cause double strand breaks
177
What is hormesis? It happens at what level of absorbed dose?
Hormesis: paradoxical, beneficial effect of low dose ionizing radiation in biological systems
Possible mechanisms:
o Stimulation of defense mechanisms like antioxidant formation and DNA repair, leading to better repair of damage after subsequent high dose radiation
o Activation of anticancer immune functions
o Bystander effect to eradicate neighbouring cells with genomic instability
178
Name the phases of mitosis and what happens to the DNA in each phase?
Prophase: chromatin condensation
Metaphase: chromosomes line up along equatorial plate
Anaphase: sister chromatids split and migrate toward opposite poles
Telophase: Chromatids reach destination, new nuclear membrane forms
179
What are the 4 stages of the cell cycle, what is happening to DNA at each stage, and which is the most
radiosensitive and radioresistant of the 4 phases?
G0/G1: DNA in euchromatin configuration for transcription
S: DNA synthesis
G2: DNA in euchromatin configuration for transcription
M: chromatin condensation for mitosis
Most radiosensitive in late G2/M
Most radioresistant in late S
180
4 R’s of radiobiology
Repair
Reassortment/redistribution
Reoxygenation
Repopulation/regeneration
181
What is the difference in cell survival curves between high and low dose rate radiation exposure. Is this
true for all types of radiation? What is the reason?
Graph of Fraction of cells surviving vs Dose (Rad or Gy)
“High dose rate is related to higher cell killing because the cells do not have the time to repair themselves.”
No. The curve is not the same for all types of radiation.
High dose: steep curve
Decrease dose: get repair, less steep
Decrease further, get reassortment/redistribution, steepens again (G2 pile-up)
Decrease dose further, repopulation: less steep
With high LET, less shoulder effect
182
Draw the cell survival curves for neutrons, Beta (-) particles and xrays with labeling of the coordinates and
identifying which are the different LET particles.
Depends on energy of neutron (high energy has shoulder, lower energy more like alpha, linear
183
describe LET and significance in radiobiology
Linear energy transfer (LET) = amount of energy deposited locally per unit track length
Significance
o Relative biologic effective (RBE) increases with LET until a maximum (100 keV/μm), then decreases
with higher LET
o Because 100 keV/μm corresponds to ionizations ~2 nm = width of DNA strand
184
Define the doubling dose and how much is it?
Dose to whole population required to double spontaneous mutation rate in population
185
Define the dose to an individual for a procedure multiplied by the number of procedures per year, what is that called?
“the overall population impact of diagnostic radiology can be assessed in terms of the collective effective dose, the product of effective dose and the number of individuals exposed.”
186
Define ‘genetically significant dose’ GSD
GSD = index of radiation received by the genetic pool
o Di = the average gonad dose for a specified type of examination for a patient in age-sex class (i)
ni = the number of persons in age-sex class (i) who had the specified type of examination during a year
Pi = the expected number of future children to an individual in age-sex class (i) o Ni = the number of persons in age-sex class (i) in the total population
187
define GSD and give GSD for x-ray, gamma ray and background
GSD = index of radiation received by the genetic pool
NCRP #93 (1987)
o Natural: 1 mSv (radon (0.1) + other (0.9))
o Diagnostic X-rays: 0.2-0.3 mSv
o Nuclear medicine: 0.02 mSv
188
In relation to carcinogenesis, define “initiation”, “promotion” and “propagation”
Initiation: mutation of DNA resulting in genomic instability
Promotion: action of a promoter (e.g., molecule) upon cell after initial mutation to induce clonal proliferation
o E.g., ionizing radiation can promote proliferation by affecting tumour suppressor gene
Propagation: stepwise transition to cancer: tumour cells undergo dysregulated proliferation due to second “hit”/mutation, with loss of tumour suppressor genes or activation of oncogenes
189
What is the Bergonie-Tribondeau rule and name 2 cell types which are exceptions?
X-rays are more effective on cells which have a greater reproductive activity:
o Therefore, cells that are rapidly dividing, undifferentiated and have long mitotic futures are most radiosensitive
Exceptions
o Small lymphocytes
o Primary oocytes
190
What is the effect of oxygen on radiation damage to cells?
Oxygen enhances radiation damage
| Oxygen fixation hypothesis: oxygen converts DNA radical to non-restorable form, preventing repair
191
What is the effect of oxygen on radiation? Define oxygen enhancement ratio (OER) & describe molecular basis of action.
Oxygen fixation hypothesis: oxygen converts DNA radical to non-restorable form, preventing repair
OER = ratio of dose under hypoxic to aerated conditions needed to achieve the same biological effect
X-ray: 2.5-3.5
n = 1.6
α = 1.0
192
What are characteristics of radioprotectors and how do they function?
Radioprotectors are chemicals that reduce the biologic effects of radiation. Sulfhydryl compounds (free SH group) such as cysteine and cysteamine work by
o free radical scavenging
o hydrogen atom donation to facilitate direct chemical repair at sites of DNA damage
193
Typical structure of a radiation protector. (What is the chemical basis of radioprotectors?) What is the mechanism?
Sulfhydryl group at one end
Base (NH2) at the other
Carbone chain in between
The most effective radioprotectors contain a sulfhydryl group, often covered by a phosphate group to reduce toxicity
194
Describe stochastic effect, deterministic effect, what is hereditary effect, cataract and what part of eye affected in cataract?
Stochastic effect-No threshold, increase in dose increases likelihood of effect but not its severity.
Deterministic effect-Threshold, increase in dose increased severity of the effect.
Hereditary effect-These are mutations that occur in the offspring of irradiated individuals. They originate in the haploid cells of the reproductive system (oocytes and spermatozoa) and are passed on to offspring that are conceived after irradiation. My not occur in the first gen., model for dose response relationship is the no threshold, linear model.
Cataractogenesis-any opacification of the normally clear lens. 2 Gy threshold, usually posterior pole of the lens in radiation induced.
195
Know the 4 syndromes of acute radiation exposure and doses, clinical symptoms associated with each.
Threshold dose for prodrome 0.5 Gy
LD50/60 in humans ~4 Gy
Minimum dose for lethality 2.5 Gy (Hall), 1 Gy without good medical care (ICRP)
1. Prodromal radiation syndrome:
o 0.5-1 Gy – early symptoms soon after radiation
o Neuromuscular
easy fatigability, apathy, listlessness, sweating, fever, HA, hypotension
o GI
anorexia, N/V, cramps, dehydration, immediate diarrhea
2. Hematopoietic syndrome
o 2.5 -5 Gy
o prodromal symptoms including N/V, followed by a latent period, then symptoms of depressed of blood elements: infection and fever from granulocyte depression; bleeding and possibly anemia caused by hemorrhage from platelet depression; anemia from RBC depression usually does NOT occur.
3. Gastrointestinal syndrome
o 5 – 12 Gy (~ 10 Gy)
o N/V, prolonged diarrhea, anorexia, dehydration, weight loss, death (5-10 days)
4. Cerebrovascular syndrome
o ~ 100 Gy
o severe N/V, disorientation, loss of coordination of muscular movement, respiratory distress, diarrhea, convulsive seizures, coma and finally death (24-48 hr)
196
Dose for bone marrow aplasia??
o TD5/5: 2.5 Gy (tolerance dose, 5% in 5 y)
| o TD50/5: 4.5 Gy (tolerance dose, 50% in 5 y)
197
Why is there a lag in the Hematopoietic Syndromes symptoms
Symptoms result from reduction in specific blood elements, which have different average life spans
Lymphopenia (1-2 days) → neutropenia (10-14 d) → thrombocytopenia (14d) → anemia (60 days)
198
In utero exposure, threshold dose of lethality at varied stages
Embryonic lethality thresholds (IAEA)
o 1st trimester: 100 mGy
o 2nd : 250 mGy
o 3rd: 500 mGy
199
What is the lowest limit of exposure for fetal death in the following stages of pregnancy: 0-2 weeks, 2-7 weeks, 8-15 weeks, 15-21 weeks, greater than 21 weeks
```
o <1 week; 0.05-0.1 Gy
o 1-8 weeks; 0.25-0.5 Gy
o 8-15 weeks; 0.5 Gy
o 15-25 weeks; >0.5 Gy
o >25 weeks; >1.0 Gy
```
200
3 main factors in radiation protection. What happens to radiation flux if you triple the distance? (What are the three most important factors in relation to gamma exposure?)
Time, distance and shielding
What happens to radiation flux if you triple the distance?
o Decreased by 1/9
```
Most important factors relating to gamma exposure?
o Time
o Distance
o Shielding
o Decay
o Energy
```
201
What affects effectiveness of shielding?
Effective Z (high Z for photon; low Z for particulate)
Density (higher density for photon; doesn’t matter for particulate)
Thickness
Type of radiation shielding against
202
What is responsible for the greatest radioactive exposure for background radiation. What is the physiologic internal radioisotope that causes the most radiation exposure in humans.
From natural background: radon
| Physiologic internal radioisotope: 40K
203
2 isotopes which cause largest amount of internal radiation
K-40
C14
204
Couple questions on Chernobyl. What the most cancer was, why the observed cancer rate was less in some, and three explanations for the same.
Most common: thyroid cancer
Cancer rates depended on:
o Heterogeneous distribution of radioactive gases and particles containing 131I
o Radioiodine consumption variable, typically from contaminated milk and produce
o Age of exposed individuals (younger more susceptible)
1.pediatric thyroid is more susceptible
205
Definition of Nuclear Energy Worker. What’s the limit of radiation exposure to pregnant NEW?
A NEW is any person who in the routine performance of their profession, business or employment will expect to be exposed to more than the prescribed limit of ionizing radiation for the general public
Public = 1mSv per year; lens 15; skin 50; hands/feet 50 (1/10th of NEW)
Pregnant = 4 mSv during course of pregnancy
NEW = 50 mSv one year, 100 mSv over 5 consecutive years; lens 150; skin 500; hands/feet 500
206
What are the laboratory rules (5) for contamination control in an intermediate lab?
Wear protective clothing and equipment (gloves, lab coat)
Do not eat, drink, store food, or smoke in this room.
Wear appropriate dosimeter at all times
In case of spill, follow emergency procedures and notify the RSO
Clearly identify work surfaces used for handling nuclear substances
After working with nuclear substances, monitor work area for contamination
Wash hands regularly and monitor them for contamination frequently
Check all packages containing nuclear substances for damage upon receipt
Store nuclear substances in a locked room or enclosure when not in use.
207
What is the radioactivity level for an intermediate lab?
Basic lab: Quantity of unsealed nuclear substance used at a single time does not exceed 5 times its corresponding annual limit on intake
Intermediate - <50x
High - < 500x
Containment level - >500x
Annual Limit on Intake (ALI)-The activity, in Becquerels, of a radionuclide that will deliver an effective dose of 20 mSv during the 50-year period after the radionuclide is taken into the body of a person 18 years old or older or during the period beginning at intake and ending at age 70 after it is taken into the body of a person less than 18 years old.
The amount of radioactivity that would deliver 20 mSv after ingestion over the 50 year period after ingestion
By definition, 1 ALI = 20 mSv/DCF (dose conversion factor)
208
Name the contamination for each class (class A, B and C)
CNSC license (non-fixed contamination in area with unsealed nuclear substance)
Removable contamination not to exceed these limits when averaged over surface area <100 cm2:
```
For controlled areas:
o 3 Bq/cm2 for class A radionuclides (Co56, Co60)
o 30 Bq/cm2 for class B radionuclides (F18, I131, I111)
o 300 Bq/cm2 for class C radionuclides (Tc99m)
```
```
For supervised public areas and for decommissioning (1/10th of controlled area dose
o 0.3 Bq/cm2 for class A radionuclides
o 3 Bq/cm2 for class B radionuclides
o 30 Bq/cm2 for class C radionuclides
```
209
Name 3 or 4 tests to which type A containers are subjected
Water spray test
Free drop test
Stacking test
Penetration test
210
For three categories of radioactive packages what are the radiation levels on the surface and at 1 meter distance?
TI = maximum radiation level in uSv/hr at 1 m from external surface of package, divided by 10, or in mSv/h multiplied by 100.
Type of label; surface (uSv/h); 1m TI
White - I < 5 < 0.5 < 0.05
Yellow - II <500 < 10 < 1
Yellow - III < 2000 < 100 < 10
211
radiation level limits at surface of 3 types of packages – know your TDG
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There are 4 types of packages.
Excepted packages
White 1
Yellow 2
Yellow 3
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212
TDG, surface dose rates for all 3 levels. (Three types of radioactive packages: name, and state maximum radioactivity at surface)
Excepted packages (UN 2910)
Radioactive I (White-I): surface dose rate <=5 uSv/h and activity >excepted package limit
Radioactive II (Yellow-II): 5 uSv/h < Package surface <=500 uSv/h and transport index <=1.0
Radioactive III (Yellow-III): Package surface >500 uSv/h or transport index >1.0
Transport index = highest dose rate (uSv/h) at 1 meter, divided by 10
Fissile
Surface contamination: surface quantities >0.3 Bq/cm2 for beta and gamma and low toxicity alpha emitters; 0.03 Bq/cm2 for other alpha emitters
213
Define the gamma constant-exposure or dose
Specific gamma ray dose constant = exposure rate per unit activity at a certain distance from a source
Unshielded dose equivalent rate at one meter in mSvh-1MBq-1
214
List 5 steps to take when opening a package containing radionuclide shipment.
CNSC Guidelines for Handling Packages Containing Nuclear Substances
o 1. If an appropriate survey monitor is available, monitor the radiation fields around the package. Note any discrepancies.
o 2. Avoid unnecessary direct contact with unshielded containers.
o 3. Verify the nuclear substance, the quantity, and other details with the information on the packing slip and with the purchase order. Log the shipment details and any anomalies in the inventory record.
o 4. Report any anomalies (radiation levels in excess of the package labeling, incorrect transport index, contamination, leakage, short or wrong shipment) to the Radiation Safety Officer.
When opening packages containing unsealed nuclear substances, additional steps should be taken:
o 5. Wear protective clothing while handling the package.
o 6. If the material is volatile (unbound iodine, tritium, radioactive gases, etc.) or in a powder form, open the package in a fume hood.
o 7. Open the outer package and check for possible damage to the contents, broken seals, or discoloration of packing materials. If the contents appear to be damaged, isolate the package to prevent further contamination and notify the Radiation Safety Officer.
o 8. If no damage is evident, wipe test the inner package or primary container which holds the unsealed nuclear substance. If contamination is detected, monitor all packaging and, if appropriate, all locations in contact with the package, for contamination. Contain the contamination, decontaminate, and dispose in accordance with the conditions of the Nuclear Substances and Radiation Devices licence.
On receipt of a package, and on opening a package, every person shall verify whether
o the package is damaged;
o the package shows evidence of having been tampered with;
o any portion of the fissile material is outside the confinement system; and
o any portion of the contents of the package is outside the containment system or the package.
215
List 4 steps to take when opening a package containing radionuclide shipment?
Document receipt of package (date, consignor, activity, etc.)
Inspect for damage or tampering
Survey: measure exposure rate at 1m and at surface
Wipe test outer surface >300cm2
(Open outer package and check for internal leaks)
216
A question on bioassay – how frequently performed for I-131 and at what level of detection a report to CNSC needs to be made.
Between 1-5 days after exposure
>= 10 kBq is reporting level
5 days after administration of treatment dose;
1000 Bq-investigation limit
10000 Bq-reporting limit
217
What are routine and non routine bioassays as determined by the CNSC (RD-58)?
o A “routine” radiobioassay is any radiobioassay that involves collecting and analyzing samples or taking measurements on the body at scheduled intervals, or at predetermined times, during normal operations.
o A “non-routine” radiobioassay is any radiobioassay that is implemented as part of an ad hoc response to a particular circumstance, such as a known or suspected intake of radioactive material due to an abnormal incident in the work place. “Non-routine” radiobioassays are often termed “ad hoc” or “special” radiobioassays.
218
What are doses for allowing a patient to be treated with thyroid therapy as an outpatient?
The actual definition is:
o Discharge and outpatient criteria should be based on the anticipated dose to members of the public (kept below 1mSv) and to the primary caregiver (kept below 5 mSv per IAEA recommendations).
o Discharge criteria at the CCI are in line with this – dose rate at 2m < 18 uSv/hr.
219
3 methods (treatments) of decreasing contamination from internal radiation?
Thyroid blockade (competitive inhibition)
Hydration/frequent voiding (physiologic excretion)
Cathartics/laxatives (direct extraction/physiologic)
220
CNSC definition of “action level”. What is the response if a situation reaches that “action level” in your practice.
Action level = specific dose of radiation or other parameters, if reached, may indicate a loss of control of part of licensee’s radiation protection program and triggers a requirement for specific actions to be taken
Response: inform the RSO, who will perform the investigation
221
What 3 things to do according to CSNC when an action level is reached?
1.Conduct and investigation and determine a cause
2.Identify and take action to restore the effectiveness of the radiation safety program
3.Notify the CNSC within the time specified on the licence.
222
```
What is the Quality Control for sealed sources containing > 50 MBq? Minor spill: < 100 exemption quantity (EQ) of a nuclear substance
Major spill:
o > 100 EQ
o personnel contamination
o release of volatile material
```
Perform a leak test in the following frequencies:
o i) For each sealed source continuously in storage - every 24 months;
o ii) For each sealed source which is incorporated in a device - every 12 months;
o iii) For each sealed source or shielding that is to be used after being stored for 12 or more consecutive months – immediately before using it;
o iv) For any other sealed source over 50 MBq (i.e. if used daily) – every 6 months.
223
If worker exposed to significant 131I dose what is the first thing you should do? In what time range should gamma probe counting be performed? When should the CNSC be notified?
If spill present, contain and decontaminate
Administer thyroid blockade (130 mg potassium iodide) and inform RSO
Gamma probe: between 1-5 days after exposure
If >=10 kBq inform CSNC immediately
If <10 kBq, >1 kBq, then include in annual compliance report
224
3 characteristics that define a major spill.
Minor spill: < 100 exemption quantity (EQ) of a nuclear substance
Major spill:
o > 100 exemption quantities
o personnel contamination
o release of volatile material
225
How is an Exemption quantity define (used to be called “scheduled quantity”)
Defined in Nuclear Substances and Radiation Devices Regulations as one of the thresholds for quantity of radioactive nuclear substance below which activites may be carried on without a licence
Exemption quantities differ for each radionuclide and are given in Schedule 1
226
List 8 steps to take with a radioactive spill?
```
Clear the area
Leave fume hood running
Close off and secure spill area
Notify RSO
Remove contaminated clothing and clean skin
Clean spill working from outside in
Wipe test for residual contamination as appropriate
Arrange bioassay if necessary
Submit written report
```
227
Tc-tagged RBC vial, what are 3 categories of materials it can be disposed of in?? What are the 3 types of waste it is considered to be (when you throw away a used
syringe with tagged RBC)?
Biologic, radioactive and sharps
228
What is the duration of a CNSC licence for therapeutic and diagnostic nuclear medicine.
5 year licence, annual compliance report
229
What are the roles of the radiation safety officer?
Availability: full-time
Training: basic radiation safety
Annual review
o Check dose limits
o Quarterly contamination monitoring
Incidents
o Investigations of contamination, overexposure, etc.
Disposal
Emergency planning
Records
Survey instrument QC
230
Who is ultimately responsible for running the hospital? How does the hospital check up on the physician?
Day to day: Executive Team, lead by President/CEO
Policy makers: Board of Directors
Level of authority may differ, e.g., some hospitals have own board, others run by health region
Hospital medical director typically oversees physician privileging and performance
231
Discuss the 4 groups of recommendations of the ICRP with regards to breast feeding discontinuation following radiopharmaceutical administrati
```
1. No cessation:
Most Tc
C14
FDG
In-111-octreotide/WBCs
```
```
2. 12 hour cessation:
TcWBCs,
Maa
Pertechnetate
RBCs
I123
```
3. 48h
TI201
4. >3 weeks
I131
Ga67
232
In what form does technetium appear in the breast? In what form does gallium appear in breast milk?
Tc-pertechnetate (10% in breast milk)
| Ga-lactoferrin
233
Radiation workers are exposed to 15,000 roentgens per hour and are exposed for a total of 1 hour. The tech is 1 meter away, the engineer is 3 meters away, the secretary is 15 meters away. What type of effects is the engineer likely to experience? The secretary is 8 weeks pregnant. What would you suggest for management for her? What is the expected effects to the tech?
```
Tech @ 1m:
o 15,000 R/h x 1h = 15,000 R
o 1 R = 0.96 rad in soft tissue
o D = 0.0096 x 15,000 R = 146 Gy
o CNS syndrome
```
Engineer @3m:
o D = 146 Gy/3^2 = 16.2 Gy
o GI syndrome
Secretary @15m:
o D = 146 Gy/15^2 = 0.65 Gy
o Counsel re: mental retardation, growth retardation
o Slight increase childhood cance risk, increased lifetime cancer risk
o >100 mGy considered threshold for therapeutic abortion
234
Patient received a high dose of 131I and was sent to OR the same night. What are the instructions that you give the surgeons regarding radiation safety?
Most of dose will be in region of urinary bladder
Minimize exposure to bodily fluids.
Wear gloves, masks, work in shifts to minimize exposure
Consider SSKI/thyroid blockade
235
Four disposal methods for radioactive waste:
Decay in storage
Release into sewer system
Transfer to authorized recipient (e.g., landfill)
Incineration/atmospheric release
236
What is iodine escape peak? What is the lead peak? What is the single coincidence escape peak?
iodine escape peak - interaction with iodine in NaI(Tl) results in characteristic X-ray (30 keV) which escapes detector; therefore, iodine escape peak @ Eγ - 30 keV
lead peak - interaction of photon with lead in collimator results in characteristic X-ray (80-90 keV), which is absorbed by detector
single escape peak - occurs as a result of pair production; annihilation of positron results in two 511 keV photons of which only 1 is absorbed in detector; occurs at 511 keV
237
If a patient is having a technetium bone scan and a thallium study on the same day, which study do you do first and why?
201Tl study first:
o Lower dose
o Less downscatter effects
238
What is z signal coming from the anger camera?
Z-signal = summation of output of all PMT, proportional to the total amount of light produced by a scintillation event in the crystal and used for pulse height analysis
239
Typical FOV for gamma camera? What affects the FOV
• Philips Brightview XCT: 50x40 cm FOV with parallel-hole collimator
240
Relationship between gamma camera efficiency and photon energy?
• Intrinsic efficiency ↓ with ↑ photon energy
241
A question asking for the frequencies of doing the following for a gamma camera: intrinsic uniformity, spatial linearity, system resolution, sensitivity.
o Intrinsic uniformity: daily (EANM, CPSA, ACR, ICANL, AAPM)
o Spatial linearity: weekly (Zanzonico, ICANL)
o System resolution: weekly (ACR, ICANL)
o Sensitivity: weekly (EANM)
242
Describe timing of various QC’s: know dose calibrator, spatial resolution, photopeak etc (Another recall: when and how do you assess: gamma camera resolution, gamma camera uniformity, gamma camera energy peak, dose calibrator linearity, dose calibrator constancy)
Gamma camera resolution
o Bar phantom weekly with a flood source
Gamma camera uniformity
o Intrinsic with a point source placed 5x detector face width away, collimator off
Gamma camera energy peak
o Tc-99m point source daily
o Set to 140 +/- 10% window
243
Describe how you would perform intrinsic uniformity test
Remove collimator
Place Tc-99m point source (<1 ml, ~18.5 MBq) in holder >= 5x crystal dimensions away, centered over uncollimated detector
Count rate <25 kcps
Acquire 10-15 million counts
Determine integral and differential uniformity (<5%)
244
Another question on intrinsic uniformity, once again define the ___ in SPECT
<1% non-uniformity for SPECT
Causes of nonuniformity;
1. Nonuniform detection efficiencies due to i.small differences in pulse height spectrum of the PMTs and ii.position dependant detection efficiencies especially in the gaps between PMTs and
2. Nonlinearities.
245
Related to the NEMA uniformity spec, how you determine integral and differential uniformity
integral uniformity = (max pixel - min pixel) / (max pixel + min pixel) x 100
o including entire field of view for UFOV and central 75% for CFOV
differential uniformity = (max pixel - min pixel) / (max pixel + min pixel) x 100
o including only the 5 contiguous pixels with greatest difference in either column or row
246
Def: angular variation in a field of flood uniformity . How would you calculate it?
Acquire flood images at multiple angles and compare. Maximum sensitivity variation should not exceed 0.75%. Note that this is no longer an issue as all PMTs are now magnetically shielded with mu metal.
247
Briefly describe how to determine angular uniformity
Tape Co-57 sheet source to the collimator face
Obtain high count tomographic acquisition over 360°C
Assess uniformity visually on raw cine images
248
Limits of non-uniformity. (What is the limit of non-uniformity for SPECT)
Depends on manufacturer recommendations, but for our centre
o Integral: CFOV: 5%, UFOV: 6%
o Differential: CFOV: 2.5%, UFOV: 3%
Also, depends whether talking about SPECT, in which case <1% after correction factors applied
249
2 types of collimation in nuclear medicine
Absorptive and electronic
250
Question on different types of collimators and their effects on the image, i.e. magnification, inversion, etc
Pinhole:
- poor efficiency (worse with distance); highest resolution; magnifies; inverts
Parallel:
- Good efficiency; 3rd best resolution; No mag; no inversion
Converging (as looking from detector out to object):
- incresing effiency until focal point; 2nd best resolution; ; Magnifies; no inversion
Diverging (as looking from detector out to object)
- efficiency decreases with distance; worst res; minifies; no inversion
251
Two changes which can be made to collimator holes to increase spatial resolution
↑ septal length
| ↓ hole diameter
252
Collimator A is considered clinically superior to collimator B. Both are made of lead with identical hole spacing and septal thickness. A has 2mm better FWHM than B. Which is more sensitive and by how much? What is the physical difference between them?
A has lower efficiency than B
Rcoll ∝ l/d, gcoll ∝ (d/l)2, the sensitivity decreases by the square of the leff while the Resolution varies linearly with it.
253
3 characteristics of collimator and how they affect performance of NaI detector
d = hole diameter: ↑d = ↑FWHM and ↑d = ↑efficiency
leff = septal length: ↑leff = ↓FWHM and ↑leff = ↓efficiency
t = septal thickness: ↑t = ↓efficiency
254
describe pinhole collimator cone depth distortion
Cone depth distortion-refers to image distortion of a three dimensional object that occurs because source planes are at different distances from the collimator are magnified by different amounts
255
Define intrinsic efficiency of a gamma camera and describe what determines it.
Intrinsic efficiency (ε) = # of radiation interacting with detector / # of radiation striking detector
Factors: detector thickness & composition, type & energy of radiation
256
Define intrinsic spatial resolution and name 3 things that determine gamma camera resolution. [French: How are these two related? What factors affect them?
Intrinsic spatial resolution = limit of spatial resolution achievable by the detector and electronics, ignoring additional blurring due to the collimator
```
Factors:
o Multiple scattering within detector
o Statistical fluctuation in distribution of light photons
o Gamma ray energy
o (Detector crystal thickness)
```
257
In a system with a given intrinsic resolution (Rins) and a non-collinearity resolution (Rnc) and a given scatter resolution (Rsca), what is the system resolution (Rsys)?
Rsys = SQRT(Rins^2 + Rnc^2 + Rsca^2)
258
What is a qualitative way of performing spatial resolution?
Using a spatial resolution phantom (e.g., 4 quadrant bar or parallel line phantom) with flood source
Note smallest bar pattern visible on image
259
Define septal penetration. What is an acceptable rate of septal penetration for adequate image quality?
Septal penetration = proportion of the off-angle photons passing through lead septae of collimator and detected in adjacent portion of scintillator
<5%
260
Filter question. Define Nyquist frequency:
The highest spatial frequency that can be resolved in an image, based on resolution characteristics of the imaging system and the parameters selected for data acquisition (i.e., 0.5 cycles/pixel)
Nyquist frequency (kmax) = highest resolvable spatial frequency
Typically set linear sampling distance (Δr) = 1/(2 kmax)
If Δr < 2 FWHM, can have aliasing
If Δr < 1/3 FWHM, sufficient sampling
If Δr > 2 FWHM, definitely will have aliasing
If Δr = FWHM, will have aliasing
If kmax significantly exceeded, may have over-sampling, resulting in lower counts per pixel, and possibly excessive noise
261
How to avoid aliasing?
Make sampling interval small enough (but may be impractical because of dataset size, computation time, etc.)
↓ FOV, with sample # of samples (so ↓Δx)
Blur input profile before recording (suppress high frequency components)
262
Describe how you choose optimal acquisition matrix. Give an example. 2 problems with assigning an acquisition pixel size which is smaller than necessary.
Spatial resolution of digital image dependent on 2 factors:
o resolution of imaging device itself (collimator/detector resolution)
o matrix size
A matrix size is chosen so that the highest possible frequency signal acquired can be fully represented (i.e. the spatial resolution limit of the system can be displayed), pixel size<1/2kmax (FWHM/3). Once this limit is met, increasing matrix size only results in increasing noise and time and memory requirements.
Set pixel size (Δr) <= 1/3 FWHM
Acquisition matrix for square planar FOV = FOV/Δr by FOV/Δr
If Δr too small:
o Too few counts/pixel high statistical noise
o ↑ pixels ↑memory usage
263
Given the MTF values of .8, .7 and .6 for three different systems at a particular frequency, which has the best response?
0.8, the closer to unity the more faithfully the image will be represented at that spatial frequency.
264
How do you calculate the MTF for the system from MTFa and MTFb.
MTFsystem = MTFa x MTFb
265
Define MTF. Qualitatively describe the relationship between MTF and the line spread function. How can knowing the MTF of different collimators affect the purchase decision
MTF = modulation transfer function, describe the spatial frequency response of an imaging system or component
o MTF is the modulus of the discrete Fourier transform of the measured line spread function
MTF helps compare the how faithfully collimators reproduce image at different spatial frequencies
266
Draw a ramp filter in the frequency domain. Draw a point spread function in one projection in the spatial domain after FBP. What are 1 difference and 1 similarity between recovery filter and low pass filter. Additional question - Draw a point source after FBP and ramp filter in the frequency domain?
Draw ramp with boxcar (i.e., truncated)
Square with black stripe
Recovery filter vs. low pass filter
o Similarity: both truncate at a maximal spatial frequency
o Difference: recovery filter amplifies medium to high spatial frequencies
SEE PAGE 157 for diagram
267
Question on what factors contribute to optimal thickness of sodium iodide crystal.
Intrinsic efficiency vs. intrinsic spatial resolution
o Thinner crystal = better resolution
o Thicker crystal = better efficiency
Energy of incident photon
268
A question on factors that contribute to decreased spatial resolution in sodium iodide detector.
```
↓spatial resolution:
o Multiple Compton scattering
o Statistical variation in light photons among PMT
o Gamma ray energy
o Detector crystal thickness
o Efficiency
o Corrections for non-linearity
```
269
What causes variation in energy resolution in a sodium iodide detector?
o Statistical variations in the number of scintillation light photons produced per keV of radiation energy deposited
o Statistical variations in # of photoelectrons released from photocathode
o Statistical variations in electron multiplication factor of the dynodes in PMT
o Non-uniform sensitivity to scintillation light over area of PMT cathode
o Non-uniform light collection efficiency for light emitted from interactions at different locations within detector crystal
o Nonlinear energy response of the scintillator
o Fluctuations in high voltage applied to PMT
o Electrical noise in PMT
270
Effect of scatter on the performance of a gamma camera?
Scatter in crystal ↓intrinsic spatial resolution
Scatter in crystal (especially escaped) likely rejected, ↓efficiency rather than energy resolution
Scatter in crystal (especially escaped) ↓count rate performance within energy window
Scatter in patient may be accepted, decreased spatial resolution
271
What is a sinogram and what is it useful for? What are the axes labelled with?
Y-axis: angle of projection
X-axis: projection profile intensity
Use: assess motion & non-uniformity
272
Besides CNR, what other types of noise are found in nuclear medicine studies?
CNR usually dealing with random noise
Structured noise: non-random, e.g., artifact relating to non-uniformity
scatter, blunders (ie. motion), systematic error (i.e. COR off)
273
What is resolution recovery? How does resolution recovery affect the recovery coefficient?
Filtering that helps to more accurately represent the intensity/activity of small hot objects (<2xFWHM), i.e., they are reduced due to partial volume effects, so resolution recovery will increase their intensity
The recovery coefficient overall improves (i.e., function rectangularizes) with resolution recovery, such that it is higher at the mid to higher spatial frequencies
274
How can resolution variability with depth in SPECT be corrected for?
Can do this during iterative reconstruction
275
Four configurations of transmission source of SPECT imaging:
Scanning line
Dual scanning line
Flood
Stationary line source with fan beam collimator
276
What are the advantages of 2D vs 3D PET and by how much is sensitivity better in 3D PET?
Advantages of 2D
o Less scatter
o Lower single count rate, fewer random events
o Reconstruction is less complicated
Sensitivities:
o 3D PET: 2-10%; 2D PET: 0.2-0.5% (4-8x) (2D is 4-8 times less sensitive than 3D)
277
Name three events/interactions on PET imaging:
o True coincidence
o Scatter coincidence
o Random concidence
278
List 2 ways to decrease random & 2 ways to decrease scatter radiation in PET?
Decrease randoms
o Delayed window method (create a delayed timing window with a time offset from coincidence timing window (CTW). Events recorded in the delayed window provides a measure of random event rate and is subtracted from the total number of coincidence events since random coincidence rate is the same in delayed and undelayed windows)
o Singles count rate method
Scatter reduction
o Gaussian fit to scatter tail
o Monte Carlo simulation method
Utilize emission and transmission images to estimate Compton scatter
o Convolution/deconvolution
279
What is “time of flight” theory? What’s the advantage of applying it to PET image?
Accurate measurement of arrival times of annihilation photons theoretically allows localization of annihilation event along line of response, but in practice, insufficiently precise to improve spatial resolution, but improves SNR
280
Questions of time of flight and crystals used and how it works and what characteristics of crystal are best for tof.
ToF PET images has higher SNR.
Need fast scintillator and electronic circuits to work. BaF2 has fast response speed, but it has lower stopping power
LYSO is the scintillator crystal used for ToF PET because it has reasonably fast response, good stopping power and good energy resolution
281
2 limitations in using TOF for image production. Which is the major one? (If TOF PET were exact, iterative reconstruction would be unnecessary. What prevents PET TOF determination from being exact? Very similar version later asked for the two factors limiting depth resolution in TOF PET.)
Crystal rise time and decay constant (major factor)
| Time jitter due to finite # of photoelectrons
282
What is the “time of flight” theory? Which crystal can be used for TOF? name 3 characteristics needed for a crystal for time of flight
BaF2 used in the past; LSO/LYSO used in existing scanners; LaBr3 being tested
3 characteristics
o Short rise and decay time
o High light output
o Good stopping power for 511 keV photons
283
Why the axial spatial resolution is different in the central axis and off center axis? In PET?
Due to depth of interaction effect
Point spread function FWHM narrowest at mid-point between detectors (with discrete, FWHM ~ d/2 at centre, d near detector)
284
Name causes of decreased spatial resolution in PET. Give five.
```
Detector width
Positron range
Noncolinearity
Depth of interaction
Reconstruction filters
```
285
What is the difference between in-plane and axial resolution in PET?
2D PET: axial is better than in-plane (due to retractable septa)
3D PET: resolution is equivalent in-plane and axial, provided detector width same in both directions
286
For a PET system with a ring of 80 cm, what is the amount of blurring in mm?
Non-colinearity: R180° = 0.0022 x D = 0.176 cm = 1.76 mm
Rsys = SQRT(Rdet^2 + Rrange^2 + R180^2)
287
What is the difference between 2D and 3D PET?
2D:
- +interslice septa; Lower sensitivity; Less scatter; Lower countrate; Easier reconstruction
3D:
- No interslice septa; higher sensitivity; higher scatter; higher countrate; More complex reconstruction
288
Why is an absorptive collimator not used in PET (2 lines)
PET relies upon electronic collimation to obtain directional information from non-absorptively collimated pairs of annihilation photons
Use of absorptive collimation would prevent many useful detector pairings and decrease sensitivity
289
Question on definitions for pulse pile-up rejection, coincidence count loss and misplacement
Pulse pile-up rejection
o When pulses in amplifier are too close together, they are summed and if amplitude is outside of PHA window, they are rejected
o Can reduce by:
Decreasing width of amplifier pulse (pulse shaping)
Measure length of pulse: if don’t return to baseline in specificied time, reject
Count loss rate
o Events not registered due to pulse pile up or dead time
Misplacement
o With high count rates, can have mispositioning due to pulse pile up (e.g., between 2 point sources)
290
5 factors affecting resolution in SPECT
```
Intrinsic resolution of gamma camera
Angular/linear sampling intervals
Shape and cut-off frequency of reconstruction filter
Photon energy
Collimator
```
291
What are 3 causes of misregistration on SPECT-CT? (3 points)
1. Respiratory motion
2. Sag of emission table
3. Patient motion between studies
4. Change in SPECT COR due to collimator weight
292
other than mis-registration, what are 3 other artefacts in SPECT/CT?
CT truncation artifact - truncation-due to the smaller field of view of the CT, inaccurate attenuation correction
Beam hardening
Partial volume averaging
Noise - large patient, low dose setting
293
Asked for minimum number projections in RBC SPECT study given 8mm hemangioma, 60cm cirumference, 7.5mm resolution of camera at 10cm, 360 degree acquisition; show math (Another: How many stops are required in a 360 acquisition to detect a 7.5mm hepatic lesion in a 200cm diameter child where the camera head is 10 cm from the child's abdomen and the resolution of the camera is 15mm) (Yet another: How many steps SPECT are required when the patient is 10 cm away from of the camera head, but their circumference is 27 cm and there is a legion that measures 7.5 mm, and the FWHM is 8mm)
```
Example 1
o FWHM = 7.5 mm @10cm
o Δr = FWHM/3 = 2.5 mm
o Circumference = πD = 60 cm
o # views = πD/Δr over 360° = 60 cm/0.25 cm = 240
```
294
Define “ring artifacts” on SPECT - what to they look like and name 2 causes
Rings of decreased or increased activity
o Non-uniformity (concentric rings, decrease in intensity toward periphery)
o Centre of rotation offset (non-concentric, full circle near centre of FOV, partial circle in periphery)
295
What causes a ring artifact, why is it more important in spect vs. planar imaging?
Non-uniformity and centre of rotation offset
| o Even small variations in non-uniformities can cause major artifact in reconstructed images
296
what’s the difference between ring artefact produced by non-uniformity and COR and why is non-uniformity significant in SPECT vs planar?
Non-uniformity: concentric full rings
Centre of rotation offset: non-concentric, full circle near centre of FOV, partial circle in periphery
o Even small variations in non-uniformities can cause major artifact in reconstructed images
297
They showed a transaxial picture of a brain? was terrible quality. then a second one which was blurred and a third one which was most blurry. Adjacent, they had another image showing point source that went to a half round circle. What is the difference between non-uniformity artifact and center of rotation artifact? Questions where: what is this artifact (COR) and how often is the QC done for this (weekly)?
• Centre of rotation offset: non-concentric, full circle near centre of FOV, partial circle in periphery
o QC weekly
298
In addition to the usual QC procedures for gamma cameras, what are 2 additional QC procedures that are required for a camera capable of SPECT?
Tomographic uniformity - High count flood-field uniformity test
COR alignment
299
Non-uniformity limit for SPECT
<1%
300
Why is uniformity more important for SPECT than planar imaging? What is an acceptable nonuniformity for SPECT? [French: Why is uniformity more important in PET than in SPECT?]
Even small variations in non-uniformities can cause major artifact in reconstructed images
<1%
301
What is the integral uniformity limit accepted for SPECT images?
<1%
302
What is the daily QUALITY CONTROL TESTS FOR PET SCANNER, describe one technique. Describe what happens when one detector is not functioning. List 2 other weekly/monthly QC procedures for PET. NOTE is specifically mentioned PET NOT PET/CT
```
Daily:
o Physical inspection
o Blank scan
Full system initialization
Baseline collection
Calibrating PMT gains
Energy test and analysis
Timing test
Emission collection and analysis
Visual inspection of 2-D sinograms
```
```
Two other weekly/monthly QC procedures for PET
o Tomographic uniformity: weekly
o Sensitivity: monthly (EANM)
o Normalization: annually
o Well-counter calibration: annually
```
303
Artifacts in FDG-PET can be subdivided into hardware, acquisition, and processing varieties. What is the most common hardware-type artifact and what does it look like.
Hardware:
The most common hardware defect is block detector failure. Its appearance depends on the loss of sensitivity and whether it is a single or multiple blocks that are affected. Overall there is a loss of sensitivity (4-5% decrease in SUV for one block 100%, up to 18% for 2 that are coincident of each other). The appearance is also dependant on the geometric position of the two detectors, however if seen the appearance is of a cold stripe following the fan angle of the defective detector(s).
304
Name 4 methods for respiratory gating? What are 2 artifacts associated with respiratory motion?
Pressure sensor elastic belt around abdomen
Spirometer measuring flow of respired air
Nasal thermistor
Infrared stereovision system tracking motion of thoracic markers
Artifacts:
o Misregistration
o Image blurring
305
What is the recovery coefficient, what is its value, what is the importance of the voxel in nuclear medicine?
RC = Measured peak activity concentration / true activity concentration
Linear sampling interval sets voxel size
Too small voxel -> low counting statistics/voxel and ↑ noise
Too large voxel -> partial volume averaging
306
Define partial volume effect. Why is partial volume effect in whole body PET imaging more significant than in SPECT?
Partial volume effect = incorrect estimation of activity concentration due to limited resolution of imaging system
o For small (<2 x FWHM) hot object, activity underestimated
o For small (<2 x FWHM) cold object, activity overestimated
In PET quantitation of activity (i.e., SUVmax) more often used to follow-up lesions
307
SUV and things that affect it.
SUV = standardized uptake value = mean activity in ROI (MBq/ml) / (injected dose (MBq) / body weight (g))
```
Factors:
o Size of ROI
o Injected dose
o Body weight
o Serum insulin
o Uptake time
```
308
List 6 things that can cause a false positive finding on PET in a patient with lymphoma.
```
False positive in lymphoma
o Inflammation/infection
o Granulomatous disease, eg sarcoidosis
o Brown fat
o Post-radiation changes
o Post-operative changes
o Marrow hyperplasia with bone marrow supportive therapy (e.g., G-CSF)
```
309
What is the effect on SUV of obesity? How would you adjust SUV calculations in an obese patient to be more realistic?
SUV = mean activity in ROI (MBq/ml) / (injected dose (MBq) / body weight (g))
Obesity not only ↑ SUV by ↑ body weight, but also, because little FDG in adipose tissue, relatively higher accumulation in lean body mass
Can use BSA or LBM as weight-indepdent indices (replacing weight above)
310
6 methodological factors that can change SUV in PET
```
Dose of FDG
Interstitial injection
Uptake period
Reconstruction matrix size, algorithm and filtering
Size of ROI
Attenuation correction
```
311
Four advantages (or disadvantages) of iterative reconstruction algorithm.
Advantages:
More quantitative
Fewer reconstruction artifacts (streak, aliasing)
More options for data corrections (scatter, attenuation, motion)
Multiple methods for reconstruction
Disadvantages
More computationally intensive
Increased noise after too many iterations
Non-linear
Can get inferior image with poor model choice
312
Name two types of iterative reconstruction algorithms.
MLEM: maximum likelihood expectation maximization
| OSEM: ordered subset expectation maximization
313
What does OSEM stand for? How is it better than MLEM? Name one disadvantage of MLEM compared to MAP algorithms.
OSEM: ordered subset expectation maximization
o Smaller # of projections -> processing time much faster
MLEM vs. MAP
o MLEM at high iterations emphasizes noise
Guaranteed convergence
o MAP produces smoother solution
Converges faster, but computationally difficult
314
Asked to look at a set of photocopied images of a SPECT phantom. Set A has increased counts in periphery and set B is more homogeneous. What changed? Attenuation correction. What are two SOFTWARE methods of doing this in the clinic.
Two software methods:
o Chang’s multiplicative with broad-beam coefficient
o Chang’s iterative method
315
Two images, and you are supposed to recognize that one has been attenuation corrected. Carry on to describe two types of attenuation correction and briefly describe them
Changs multiplicative and iterative methods,
multiplicative-using an idealized image or the non-corrected image, assume standard linear attenuation coefficient and calculate an ACF for each point on the matrix and apply (good for homogeneous structures);
iterative-obtain the corrected image as previous, forward project, subtract these from the acquired projections and FBP to produce the error image, apply the ACFs to the noncorrected and the error image and add together.
Monte-Carlo method-mathematically model the attenuation at each point in the matrix.
CT attenuation correction or transmission rod source attenuation correction-attenuation map is produced by calculating the projection profiles of attenuation using a blank image and a image of the patient, this it FBP to form the map which can be applied to Changs methods or more commonly to iterative recon methods.
316
Two sealed tracers for PET attenuation correction:
Ge-68, Cs-137
317
Name four types of attenuation correction in PET and briefly describe
68Ge rod source: pre-, post- or simultaneous transmission scan
137Cs rod source: pre-, post- or simultaneous transmission scan
Transmission CT: pre- or post-scan
o Scale using bilinear method to equivalent attenuation for 511 keV
Chang method: assume uniform attenuation for attenuation correction factor
318
Three types of attenuation correction for PET and briefly describe advantages and disadvantages of each.
CT transmission map
o ADV: rapid acquisition,high photon flux
o DISADV: discrepancy in energies, radiation dose
Rod Source transmission map
o ADV: longer acquisition time, cheaper, closer energies
o DISADV: low photon flux, high contrast
Chang Method
o ADV: fastest, cheapest
o DISADV: assumes uniform attenuation
319
Differences between attenuation in SPECT and PET images.
In SPECT, source to detector distance is important
Tissue attenuation at SPECT energies, has large component contributed by photoelectric, vs. Compton for 511 keV annihilation photons for PET
PET more susceptible to attenuation artifact
320
Three methods of scatter correction in SPECT.
Energy window methods
First order Chang multiplicative with broad beam geometry
Convolution subtraction: spatial analysis method based on the line spread function
321
Define beam hardening on CT & give 2 consequences of beam hardening
Selective absorption of low energy X-rays in highly attenuating materials results in increased average energy of transmitted beam
Consequences:
o Interfere with attenuation correction in SPECT
o Artifacts like cupping or streak
322
Give an example of a smoothing kernel (3 x 3 matrix with central value of 4). What is special about a Laplace filter?
1,2,1
2,4,2
1,2,1
Laplace: edge detection filter, identifies zero-crossing of second derivative
323
A set of 7 numbers (3,4,5,6,6,8 or something), and give the mean, median and mode. Define each. (Define mean, median, and mode. Calculate mean, median, mode for the series 1,2,4,5,6,6,7)
Mean = average
Median = Median: middle value in ordered set, if odd number; mean of middle two in ordered set if even
Mode = Most commonly occurring value (may have multimodal sets, if more than 2 modes)
324
describe continuous data and give 2 examples
Continuous data can have any value within a certain range
o Weight
o Height
325
describe discrete data and give 1 example
Discrete data can only have certain values over a range
| o Population
326
What is the definition of power of a study?
Probability that a statistical test will reject the null hypothesis when the null hypothesis is false
327
Questions on ROC and MTF:
MTF is the discrete Fourier transform of the line spread function
ROC: TP fraction (Sn) vs. FP fraction (1-Sp)
ROC: TP fraction (Sn) vs. FP fraction (1-Sp)
AUC of ROC = accuracy
328
describe how to construct a ROC curve
Plot the sensitivity (True positive rate, y-axis) vs. 1-specificity (True negative rate, x-axis) for a series of experiments of a test with different cutoff values. The one that deviates most from the straight line represents the most accurate test.
329
Define Bayes Theorem
Bayes theorem states that the probability of theorem given new data (posterior prob)=(prob of the new data given the hypothesis (conditional prob)*probability of the hypothesis being true before the new information (prior prob)/prob of seeing that data (marginal prob)
330
using TP, FP, TN, FN define: sensitivity, specificity, PPV, NPV, accuracy, true positive fraction
```
Sensitivity (= true positive fraction) = TP / TP + FN
Specificity = TN / FP + TN
False positive fraction = 1-specificity
TPF vs. FPF are the axis of the ROC
PPV = TP / TP + FP
NPV = TN / FN + TN
Accuracy = TP + TN / TP + TN + FP + FN
Additional derived rates:
False positive rate = FP / TN + FP
False negative rate = FN / TP + FN
```
331
What does a p>0.05 indicate
P value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed, if the null hypothesis is true
At a significance level (alpha) of 0.05, a calculated p value >0.05 would not be considered significant, and therefore the null hypothesis would not be rejected
332
For a given number of ___ counts in a single pixel, what is the signal to noise ratio for that pixel?
N / SQR N
333
Calculate the minimal detectable activity (MDA). Values given for: background count rate, confidence interval required (95%) and counting efficiency (mCi/cps).
MDA = 3*SQRT(Rb/t)
```
Rb = background count rate
t = counting time
```
Get cps, then divide cps by sensitivity of device to get activity
334
Best statistical test for comparing proportions
Chi squared
335
What is a positive likelihood ratio? What does it represent?
Likelihood-ratio positive = sensitivity / (1 − specificity) = Odds of disease after +ve test / Odds of disease before the test
LR(+) the likelihood that +ve test result would be expected in patient with disease/the likelihood that +ve test would result in a patient without the disease.
LR(-) the likelihood that –ve result result would be expected in patient with disease/-ve result in a patient without disease.
336
If the likelihood ratio is 10, what does this mean for a positive test that detects lung cancer?
Odds of lung cancer after +ve test is 10x higher than before test
337
A worker has developed cancer and you are asked to advise the jury/courtroom about the probability of the patient developing cancer because of his work. Is there an equation you could use to define the probability that the cancer is work related?
Probability of causation analysis to estimate a posteriori probability that radiation caused a particular cancer
o PC = (excess cancer rate due to radiation) / (excess cancer rate due to radiation + baseline risk) x 100%
338
Be able to calculate % uncertainty – was given an EF calculation and also asked to calculate the standard deviation.
EF = [(EDC – bk) – (ESC – bk)] / [EDC - bk]
%error: SEE PAGE 196
339
What is QALY? List 4 ways to monitor health outcome? What is the justifiable cost for QALY?
QALY = quality adjusted life year = 1 year of life x utlity value (utility value = 0 for death, 1 for perfect health)
4 ways
o Mortality
o Morbidity
o Disability adjusted life year (DALY) = years of life lost + years lived with disability
o Health-adjusted life expectancy (HALE) = average number of years that an individual is expected to live in a healthy state
No clear-cut threshold, but values like $100,000/QALY have been suggested for advanced economies
340
Calculate effective half life of Tc-99m tracer giving varied excretions (sum of the excretion is about 50% at 5 hours)
Teff = TpTb/(Tb+Tp) = 2.7h
341
Define the term effective half life
Teff = time for initial administered dose to be reduced to ½ of original by both physical decay and biological elimination
342
Describe in vivo neutron activation analysis.
Identifies the abundance of specific elements by distinct gamma ray spectra emitted after neutron activation
Immediate or concurrent measurement for reactions with short decay half lives (prompt gamma)
Longer lived products analyzed by delayed gamma
343
Five currently used methods for labelling red blood cells and their labelling efficiency
```
in vitro (Ultratag) - 98 %
in vitro - 95%
in vivtro - 90 - 95 %
in vivo - 70 - 80 %
51Cr labeling - 90%
59Fe labeling
111-In-oxine
14C-glycine
```
344
What is the most commonly employed method of RBC labeling and what is its labeling efficiency? What are 3 drugs which can interfere with labeling efficiency by the in vivo method?
Ultratag kit >98%
```
In vivo interference:
o Heparin
o Doxorubicin
o Digoxin
o hydralazine
o iodinated contrast media
o penicillin
```
345
Causes of poor RBC labeling:
1. Heparinized patient - Complexes with pertechnetate leading to renal excretion
2. Chemotherapy - disrupts RBC membrane
3. Injection through iv - Adherence to wall of iv
4. Generator ingrowth time > 24 hours - Presence of excessive Tc99 from decay of Tc99m
5. Decreased hematocrit - Tc-99m is reduced outside the RBC
346
Three ways of labeling RBC’s. Briefly describe each method. Name an advantage, a disadvantage and the efficiency of each method
1. In vivo:
Inject SnPYP IV
Wait 20 min
Inject TcO4- IV
Advantage = No handling of blood products
Disadvantage = lowest labelling efficiency (75-90%)
2. Modified in vivo/in-vitro
Inject SnPYP IV
Wait 20 min
Withdraw blood into syringe containing TcO4-
Wait 10 min
Reinject
Advantage = Higher labeling efficiency than in vivo (85-95%) without need to separate blood from patient
Disadvantage = Suboptimal labeling efficiency
3. In vitro
Incubate blood with Sn citrate 5 min
Add sodium hypochlorite, then ACD
Add TcO4- 20 min
Assess purity, reinject IV
Advantage = Highest labeling efficiency (>97-98%)
Disadvantage=Most handling of blood products
347
In RBC labeling with pertechnetate:
a) Name two reducing agents
b) What happens to Sn once it is used to reduce pertechnetate?
c) Which part of the RBC does pertechnetate bind to?
d) What is the mechanism of entry of pertechnetate in the RBC?
a) Stannous citrate, stannous gluceptate, stannous pyrophosphate
b) Sn2+ is oxidized in the reaction (redox reaction)
c) 80% β subunit of hemoglobin, 20% heme directly
d) Enters via the bicarbonate-chloride anion exchanger (band-3 protein or Anion exchange 1)
348
5 assumptions in assessing blood volume
Small enough volume to not affect blood volume
Remain within vascular space
Even distribution/uniformly mixed
In steady state equilibrium at time of measurement
Stable, not metabolized
349
Want to design a new tracer for blood volume measurements using dilution? 3 properties it was to have (3 points)
Volume of tracer sufficiently small to not alter the volume to be measured
Ideally remains within space of interest
Easily measurable quantitatively
350
Most popular label for red cell survival studies. If red cell survival is normal (mean 120 days) what is half-time value for this study? Why is there a difference? 3 locations of measurement if associated sequestration study
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51Cr-EDTA
Half time = 60 days
Difference from 1% elution/day of 51Cr-EDTA from RBC
Locations of measurement
o Liver
o Precordium
o Spleen
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351
Problem with chromium 51 in RBC labeling.
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Problem: not stable
o early loss from damage
o 1% elution/day after
Eγ = 320 keV (9%)
T½ = 30 d
Labeling efficiency: 80-90%
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352
What is the normal RBC survival half time on Cr-51 labelled RBC survival test? This is different from the actual RBC survival half time - explain.
Normal RBC survival: 90-120 days
Theoretical half-life of RBC labeled with Cr-51: 50-60 days
Measured half-life of RBC labeled with Cr-51: 25-35 days
Difference is due to:
o 1% elution of Cr-51 from tagged RBC’s per day
o RBC damage during labeling
o Poor labeling
353
4 causes of decreased RBC survival or half life in survival study
Intracorpuscular defects
o Spherocytosis
o Sickle cell disease
Extracorpuscular defects
o Autoimmune hemolytic anemia
o Disseminated intravascular coagulation
354
Define f-cell ratio. What range exists for this quantity in the literature?
F- cell ratio: ratio of whole body hematocrit to venous hematocrit
Varies, anywhere from 0.82-1.0
355
A 4 year old weights 17 kg and with surface area of 0.71 m2, calculate theoretical value of (1) urinary bladder capacity; (2) dose of Lasix; (3) dose of captopril; (4) GFR:
Urinary bladder capacity: (age+2) x 30 ml = 180 ml
Dose of lasix: 1mg/kg
Dose of captopril: 1 mg/kg max of 25 mg
Adult levels reached by 6 mo-1y, so:
o GFR = 100-120 ml/min/1.73 m2 x 0.71 m2 ~49 ml/min
356
Explain the method of GFR determination using the monoexponential, 2 blood sample technique
Use detectable GFR agent in IV bolus
Sample plasma at 2 time points
Estimate GFR from plasma clearance by fitting values to monoexponential curve (P(t) = P(0) e-λt)
GFR ~ plasma clearance = Dose/(Area under curve)
A monoexponential method implies a single compartment model, the solution to which is an exponential decay in tracer concentration in plasma
With 2 data points, we can obtain a curve-fit of the exponential curve with a single time constant, which then allows determination of the AUC and plasma clearance rate
357
DTPA with excess pertechnetate – impact on quantitative GFR.
TcO4- cleared much slower than DTPA; so will underestimate plasma clearance and therefore GFR
358
How to do C-14 breath test
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Swallow capsule intact
Wait 10 min
Exhale into Mylar balloon
Add to vial containing hyamine and ethanol with phenolphthalein pH
If solution turns pink, adequate collection (indicates pH drop)
Add liquid scintillation cocktail
Read on liquid scintillation counter
>200 dpm is positive
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359
In Schilling’s test, why 0.5 μg B12 is used?
Don’t want to saturate the distal ileal receptors and cause non-IF mediated uptake
360
What are the neurological symptoms of B12 deficiency?
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o Posterior column dysfunction (subacute combined degeneration of spinal cord)
loss of position and vibratory sense
o Dementia
o Peripheral neuropathy
o Weakness and ataxia
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361
What two biochemicals can be measured in urine or blood to confirm B12 deficiency?
o ↑ homocysteine & methylmalonic acid levels in blood and urine
362
Briefly describe the pathophysiology of B12 deficiency in the following conditions, naming the involved transport protein or receptor protein:
o Vitamin B12 absorption:
– Terminal ileum unable to absorb (↓cubam receptor)
– Ingested B12 is released from protein by digestive enzymes (gastric acid & pepsin)
– B12 binds to R protein in stomach (R protein found in gastric, biliary & salivary secretions)
– Pancreatic enzymes degrade B12-R & facilitate binding of B12 to IF in the presence of alkaline pH
– IF is produced by parietal cells in the fundus & body of the stomach
– B12 –IF is absorbed by the terminal ileum
– B12 enters serum bound to transcobalamin-I (75%) & transcobalamin-II (25%)
o Zollinger-Ellison syndrome:
– Low intestinal pH interferes with release of B12 from B12-haptocorrin complex
– Results in low intestinal pH & this interferes with release of B12-R protein and binding to IF
o Crohn’s:
– Inflammation ↓cubam receptor in terminal ileum
o Pancreatic insufficiency:
– ↓ protease in bowel to cleave B12-haptocorrin complex for intrinsic factor to bind
– impaired protease release of B12-R protein to bind to IF
o Cobalamin deficiency:
– In chronic deficiency, ↓cubam receptor in terminal ileum
– chronic B12 deficiency leads to alteration in small bowel mucosa, ie less IF-Vitamin B12 receptors in terminal ileum
o Atrophic gastritis (pernicious anemia):
– ↓ production of intrinsic factor
– impaired gastric release of food bound B12 and decreased production of IF
363
Name the activity and mass of B12 given for the shilling’s test.
o 0.5 μCi 57Co-cobalamin in <1 μg
| o 0.5 uCi (18.5 KBq) Co-57 labeled B12 not exceeding 1 ug
364
When do you get the maximum urine excretion of B12?
o 8-12h (Henkin)
365
What are 3 causes of falsely low B12 measurement on shilling’s test?
o Incomplete urine collection
o Renal failure
o Chronic B12 deficiency
366
Shilling test questions (these were on the basic sciences section!) Give the maximum radioactivity dose, the flushing dose, indicate why to collect urine pre-study. When is the maximal urine excretion?
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0.5 μCi 57Co-cobalamin in <1 μg
Flushing dose: 1 mg B12 IM
Pre-study urine (12h before): to rule out prior radioisotope procedure
Maximal: ~8h
Normal >9%
Abnormal <7%
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367
Five pathophysiologic causes of vitamin B12 deficiency and disease states which can cause this.
Food: B12-deficient intake
Stomach: pernicious (lack of intrinsic factor), congenital defect in intrinsic factor, partial or gastrectomy, atrophic gastritis
Pancreas: chronic pancreatitis (insufficient proteolytic enzymes to cleave B12-haptocorrin complex)
Jejunum: bacterial overgrowth, parasites (competitive consumption) and sprue
Ileum: ileum resection, Crohn’s disease, chronic B12 deficiency (↓cubam receptor)
368
Basic questions on B12 test preparation
Check serum B12, folate, homocysteine and methylmalonic acid levels
Overnight fast
No recent B12 treatment
Confirm no prior Nuclear medicine study
Collect urine 12h before to ensure no other radioisotope
369
75SeHCAT Breath test!!!!! how is tracer administered, how is it measured? THOSE bastards
Oral capsule (10 μCi = 370 kBq)
Uncollimated gamma camera
o Image head to thigh, 1-3 h after ingestion
o Repeat scan at 7 days
Retention >15% normal
Retention <10% abnormal, suggest bile acid malabsorption
370
Very brutal question on bone kinetics using MDP – name two tests for quantitation. Another part – what is the typical whole body retention of MDP at 24 hours?
2 tests:
o 24h whole body retention (whole body counting at baseline and 24 hours; if no whole body counter, can do 24h urine collection, confirmed with 51Cr-EDTA)
o Modified Brenner method (gamma camera based, using adductor ROI to track soft tissue curve)
Typical retention ~30% @24h (assuming normal GFR in adult)
Tracers: 99mTc-MDP (bone tracer) and 51Cr-EDTA (GFR tracer)
371
What assumptions are made with regard to the tracer in tracer kinetic studies.
Tracer properties
o No isotope effect
o Trace quantity, to not perturb system
high specific activity
o Mimics biochemical or physiologic process/compartment
o Stable, or metabolized like endogeneous biochemical
System:
o Steady state
o Instantaneous and complete mixing
372
Define compartment as used in tracer kinetic studies.
Volume or space which behaves as a single, homogeneous, well-mixed distinct component of the overall biological system, which can be physical space, distinct chemical form or pharmacologic state
373
Using bone density measurement as an example, define regression to the mean:
Given serial measurements of BMD in an individual, actual measurements fluctuate around a “mean value”
For a single measurement, if the BMD is measured above the mean, there is a high probability a subsequent measurement will show a lower BMD that reflects the regression to the mean.
374
variables to assess in acceptance testing of DEXA machines
Leakage radiation and scatter radiation exposure rates (controlled area <0.4 mSv/wk, uncontrolled <20 μSv/wk)
HVL determination with Al sheets to assess beam quality
Entrance skin exposure using dosimeter/chamber
Precision and accuracy with step-wedge phantom
X-ray tube voltage and current determination
375
At what 4 points in an ISCD certified institution should a technologist should their precision be assessed?
1. One complete precision assessment after basic scanning skills have been learned
2. Precision assessment after having scanned at least 100 patients
3. Repeat precision assessment if a new DXA system is installed
4. Repeat precision assessment if a technologist’s skill level has changed
376
You purchase a new DXA with 0.002 g/cm^2. List 4 quality control procedures you would perform and the least significant change you would accept.
P– precision – long term precision error, coefficient of variation
C – constancy – phantom measured every day, values are plotted on Shewart chart or Cusum mask.
L – linearity – samples of bone ashes of increasing quantity are measured and plotted vs measured BMD
A – accuracy – measure a phantom whose precise composition is known (usually bone ashes).
G – geometry – check photopeak of X-ray source, check for beam distortion or beam hardening
Least significant change should be determined from precision error by precision assessment, not from manufacturer’s specifications; ISCD 2007 position statement:
o Lumbar spine: 5.3%
o Total hip: 5.0%
o Femoral neck: 6.9%
377
List 3 things to include in a quality control program for a DEXA facility
Calibration (daily)
Phantom scanning (weekly)
Precision assessment
378
Define T and Z-scores in relation to children
T-scores not used for children
Z-score = #SD away from age and sex matched normal population
Low bone mineral content/density is Z-score <= -2.0
Osteoporosis diagnosed on the basis of both significant fracture and Z<=-2.0
379
Define T-score and Z-score. How do you calculate least significant change?
T-score = (BMDpatient – BMDyoung normal female reference)/SDyoung normal female reference
Z-score = (BMDpatient – BMDage-matched reference)/SDage-matched reference
LSC = RMS-SD x 2.77 (i.e., 95% confidence interval)
Root mean sqaure-SD determined from scanning 15 patients 3x each or 30 patient 2x each
380
List 8 causes of abnormal results on BMD
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Falsely increased:
o Compression fracture
o Degenerative changes – osteophytes
o Severe aortic calcification
o Severe scoliosis
o Blastic metastases
o Surgical hardware
o Overlying objects
o IV / oral contrast
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Falsely decreased:
o Previous laminectomy
o Lytic lesions
o Improper technique (typically increases but can decrease with hip positioning)
381
List the 3 most common causes of osteoporosis in men other than hyperthyroidism, malabsorption
Alcohol, smoking, steroids, hypogonadism
382
What are the types of osteoporosis and the causes of Type I?
* Osteopenia: decrease in mass of normal bone but no increase in risk or incidence of fragility fracture.
* Osteoporosis: decrease in mass of normal bone (mineral and matrix) which results in compromised bone strength predisposing to an increased risk of fragility fracture.
* Primary Type I (Post menopausal) = ↓ estrogen secretion →↑IL1, 6, TNFa → ↑osteoblast/clast → ↑resorption,
• Primary Type II (Senile osteoporosis) – typically after age 70, women 2x as affected as men.
o Thought to be related to increased parathyroid function or VitD resistance / deficiency
383
Give 5 indications for doing a bone densitometry.
All menopausal women aged > 65 yo
Premenopausal women > 40 yo with at least one fragility fracture.
Men > 70 y.
Patients followed for osteoporosis
Drugs predisposing for osteoporosis (steroids, dilantin, barbiturates, alcohol, tobacco etc)
Disease predisposing for osteoporosis (Cushings, hyperthyroid, hypogonadism, IBD, celiac disease)
