Physics/Radiopharm Flashcards

Question

Parts of cyclotron

Answer 1

Ion source, dees, gap, magnets, vacuum, stripping foil, target

Answer 2

Mo99 breakthrough: Assessed with each elution by placing sample in a 10HVL lead shield (2mm for Tc99m; to attenuate 140keV gammas), and detecting 740 & 780keV photopeaks in dose calibrator. The upper limit is 0.15 kBq/MBq at the time of injection (may be exceeded in emergency situations). Because Mo99 decays slower, the ratio of Mo99 to Tc99m increases with time. i. Can also perform with phenylhydrazine solution: Mo-Ph complex causes a color change, which can be quantified by colorimetric test.

Answer 3

Al breakthrough: excess Al3+ induces flocculation (aggregation) of Tc99m-SC and agglutination of Tc99m-labeled RBCs, potentially resulting in liver and/or lung embolization, as well as image degradation. Al3+ is therefore limited to 10ug/mL by colorimetric spot test using aurin tricarboxylic acid or methyl orange, which is performed on each eluate.

Answer 4

Leads to flocculation of SC, agglutination of RBCs, and lung uptake in bone scan

Answer 5

Heparin, penicillin, iodinated contrast media, dextran, doxorubicin, hydralazine (can oxidize stannous ion)

Answer 6

a. Thiosulfate is the source of sulfur for SC formation in acid. b. Gelatin is a protective colloid (a “stabilizer”) which coats the negatively-charged sulfur particles with a charged protein sheath, causing them to repel one another. c. EDTA is added to the kit to chelate excess Al from Tc elution (Al flocculates SC).

Answer 7

``` B I E B E R : B= bifunctional chelating agents I= Introduction foreign label E= exchange of isotope B= Biosynthesis E= excitation labeling R= recoil labeling ```

Answer 8

Indirect method: | Xe-124 (p,2n) Cs-123 -> Xe-123 -> I-123 This will be I-124 carrier free.

Answer 9

Proton bombardment of enriched Te-124 can yield I-123 but not ideal because can be contaminated by I-124 and I-125.

Answer 10

a. O18(p,n) gives fluoride ion in aqueous solution, higher specific radioactivity and better for FDG production, but O18 water is expensive. b. Ne20(d,α) gives elemental fluorine gas, cheap and better for F-dopa production, but lower specific radioactivity.

Answer 11

No carrier added - A preparation of a radioactive isotope which is essentially free from stable isotopes of the element in question. Advantages: - Permits more efficient and high specific activity labeling with the therapeutically active 131-Iodine isotope which could result in maximum delivery of the therapeutic potential of I 131 MIBG - Minimizes the amount of non-radioactive MIBG molecules administered to the patient, potentially reducing pharmacologic toxicities, especially cardiovascular events or toxicity, and possibly enabling better tolerated and effective treatment

Answer 12

a. Carrier: non-desirable contaminant radioactive or non-radioactive species in solution with the desired species. b. Specific activity: proportion of a sample that contains only the radioactive form of the atom, expressed in Bq/g. c. CFSA (Bq/g) = lambda*N = ln2/T1/2 * 6.022x1023/atomic weight (remember to convert T1/2 to sec)

Answer 13

Radiochemical purity is the fraction of total radioactivity in the desired chemical form in the radiopharmaceutical. Impurities include free and hydrolyzed Tc-99m TcO4- 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 Incomplete reaction o Radiolysis

Answer 14

- solvent extraction - ion exchange - paper, gel, thin-layer or high performance liquid chromatography - gel electrophoresis - precipitation - distillation

Answer 15

A) fraction of total radioactivity in the desired radionuclide form. (Mo99 breakthrough) B) fraction of total radioactivity in the desired chemical form. (HR and free tech.) C) Presence or absence of contaminating chemicals (e.g. solvents in FDG synthesis). D) Biologic purity: sterility and apyrogenecity.

Answer 16

Sr–82 and Sr-85 breakthrough

Answer 17

Limit is 0.15 uCi 99Mo/mCi 99mTc (0.15 kBq/MBq) at the time of administration. Saha, page 77 The 99Mo contamination is measured by detecting 740-keV and 780-keV photons of 99Mo in a dose calibrator or a NaI(Tl)detector coupled to a pulse height analyzer. The eluate vial is placed in a lead pot (about 6-mm thick) to stop all 140-keV photons from 99mTc and to count only 740-keV and 780-keV photons from 99Mo. The shielded vial is then assayed in the dose calibrator using the 99Mo setting. Molybdenum-99 along with 98Mo (from the molybdenum target) can also be detected by adding phenylhydrazine to the eluate and observing the color change due to the Mo-phenylhydrazine complex by the use of a colorimeter.

Answer 18

Using Fission MOLY in generator 99Mo → 99mTc + β− + νe Cyclotron produced 100Mo(p,2n)99mTc

Answer 19

The solution should be clear, colourless, and free of visible foreign material. 0.15 kBq/MBq, 0.10 ug/mL 12 hours 2 weeks

Answer 20

It will cause oxidation and radiolysis. The Tc99m still in the generator will also decay, leaving more Tc99 and decreasing the specific activity of your next elution. Also, possibility of pseudo-channeling is created by leaving the column wet. You can try to elute remaining fluid with another vacuum-vial.

Answer 21

Co-57 cyanocobalamin (Vitamin B12) | C-14 Xylose

Answer 22

Tc-essential – Tc is integral part and for which the molecule would not be delivered to target in the absence of the Tc (prepared by integrated approach). Biodistribution depends of their physico-chemical properties (charge, size, lipophilicity) E.G. MAG-3, ECD, HMPAO, Sestamibi. Tc tagged - non-substrate specific localization mechanisms. Technetium is labeled or “tagged” to a variety of molecular species that delivered technetium to organs of interest by simple diffusion, phagocytosis, entrapment, or cell sequestration mechanisms. Technetium is a passenger atom not essential for localization. include complexing agents (e.g. DTPA), particles (e.g. sulfur colloid), blood cellular elements (e.g. leukocytes), and proteins (e.g. human serum albumin).

Answer 23

Tc-essential is integral part of the molecule and without it, it will not have desired in vivo effect. Examples: HMPAO, ECD, MIBI, TETRAFOSMIN, HIDA, MAG3. Tc-tagged does not need Tc atom to carry function. Tc is added to side-branch with no effect on receptor site or is attached to bifunctional chelate. MAA, SC, DTPA, RBC.

Answer 24

+7 to -1 oxidation states are possible. +7 is the most stable (+4, +5, and +7 are the most common; +4 if I had to pick one, but not sure). Add pyrophosphate-Sn to carry tin inside and reduce Hgb. Pertechnetate then added and goes inside cell and get reduced by Sn. The Tc then binds B-hemoglobin and heme.

Answer 25

60 000 vs. 100000 (debated)

Answer 26

Pyrogenicity: ability of substance to induce fever - Rabbit test and limulus amebocyte lysate test BEST IS Limulus amebocyte lysate test - o No live animal testing - o Rapid result (1 hour) - o Less radiopharmaceutical needed

Answer 27

LAL/ BET test derived from horseshoe crab blood cells (amebocytes): Gram-negative endotoxin activates proenzyme to coagulase, which in turn activates coagulogen to coagulin. The gel-clot method and the chromogenic method are comparable. b. More sensitive than rabbit testing; cheaper; faster; easier; more ethical (?)

Answer 28

Pulmonary Hypertension Pediatric Known R to L Shunt

Answer 29

a. In vitro is most at >97%, modified in vivo >95%, in vivo ~85%. b. Sn2+

Answer 30

a. Mo99 breakthrough (radionuclide purity) b. Al breakthrough and pH (chemical purity) c. HR tech (radiochemical purity)

Answer 31

- Bombarding particle typically has +1 (proton) or +2 (deuteron) charge (though most cyclotrons now are negative-ion cyclotrons) - In a (p,n) reaction, presumably you’re gaining a charge. - They are shifted to the proton-heavy side - They decay by positron or EC. - Isotopic purity is high. - Radionuclidic yield is low. - Cost is high.

Answer 32

a. stripping foil is near 100% efficient, so get less radioactivity in the housing. b. Better beam optics. c. The foil can also split a beam, so you can create 2 different products at once. d. Smaller than positive ion cyclotrons e. Disadvantage: need a lower-pressure vacuum.

Answer 33

a. Chelation: The formation of attractive interactions between two or more separate binding sites within the same ligand and a single central atom (usually a metal). b. BFCA: reagents containing a strong metal-chelating group and a chemically reactive functional group

Answer 34

1x1x0.1mm = 0.1mm3 = 0.0001mL, so 110/0.0001mL = 1,100,000/1mL

Answer 35

B-amyloid plaques, labeled with 11C.

Answer 36

a. In an ionization event, an electron (delta ray) is ejected from its atomic orbit by an incident charged particle, and has enough energy to cause secondary ionizations on its own.

Answer 37

a. Compton scatter | b. Photoelectric absorption

Answer 38

Iodine escape peak: photoelectric absorption of an incident photon by iodine in the crystal emits a 30keV characteristic x-ray. When this x-ray is not absorbed, the resultant energy deposited is 30keV less than the photopeak. This happens more commonly for low-energy photons (<100keV).

Answer 39

It is one of the possible interactions between photons and matter, where the atom absorbs all energy of incident photon and an orbital electron is ejected. It is the dominating effect in heavy elements at low photon energies. Probability of photoelectric effect α Z3/E3. The photoelectric component increases abruptly at energies corresponding to orbital electron binding energies of the absorber elements (K absorption edges)

Answer 40

Detection of compton scattered events reduces image quality Compton scatter: photon interaction with outer shell electron resulting in deflection of photon and ejection of electron Can reduce intrinsic spatial resolution. Intrinsic spatial resolution is the limit of spatial resolution achievable by the detector and electronics, ignoring additional blurring due to the collimator. It is limited primarily by 2 factors: Multiple scattering of photons within the detector: if a photon undergoes Compton scattering within the detector crystal and the residual scattered photon is also detected, but at some distance away, the two events are recorded as a single event occurring at a location along the line joining the two interaction sites. For photon energies less than 300 keV this is not significant.

Answer 41

HVL is the half value layer or the amount of a material necessary to attenuate half of the incident radiation *Dependent on type/density of material and energy/type of incident radiation *Assumes narrow beam geometry Examples in lead: 99mTc: 0.03 cm 67Ga: 0.07 cm 60Co: 1.6 cm

Answer 42

a. Half-value thickness (thickness of a material that absorb 50% of an incident beam) b. Z and density of material, and energy and type of incident beam

Answer 43

at installation, daily, after servicing. Use Cs-137 (long-lived) +/- 10%

Answer 44

Accuracy, linearity, constancy, geometry. Shielding is used for linearity.

Answer 45

a. Battery check – display on screen b. Background – performed in an area remote from radioactive sources (to ensure meter is not contaminated) c. Constancy – using long lived source, should be within +/- 10%

Answer 46

Battery check Background Constancy? Physical inspection (EANM)

Answer 47

· 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 photons -> more ionizations) GM counter is a gas-filled (argon + quenching gas) detector designed with high voltage across the chamber. · when ionization occurs, the accelerating electrons in addition to ionizing gas molecules, also cause excitation of gas molecules which in turn release UV photons. The UV photons undergo photoelectric absorption and more electrons are emitted, causing an avalanche ionization. The Geiger discharge continues until a band of slow-moving positive charges around the anode reduce the effective electric field, dropping it below the level needed for gas amplification. · GM counter CANNOT distinguish different energies

Answer 48

1. Give up electrons easily 2. When they are neutralized by electrons entering higher energy orbits, they deenergize themselves by dissociating into molecular fragments rather than by emitting UV photons 3. Strong absorbers of UV radiation

Answer 49

1. To be able to compare counting rates between two samples, because sample volume/geometry has a significant effect on counting rates. 2. To maintain constant geometric efficiency. The fraction of gamma rays escaping the well (and the geometric efficiency) depends on the position of the source in well. Differences in volume and geometry affect the position of the source in the well and will therefore affect counting rates. Sorenson p. 197

Answer 50

Well Counter: DAILY Q/C: background adjustment, constancy (with long-lived reference source) QUARTERLY Q/C: Energy resolution (FWHM) ANNUAL Q/C: Efficiency (cpm/Bq) ref source +/- 5% Dose Calibrator: says +/-10 % in Saha?? DAILY Q/C: Constancy (reference source +/- 5%) QUARTERLY Q/C: Linearity (shielding or decay method +/- 5%), Accuracy (2 radionuclides +/- 5%) After repair/recalibration: Geometry (+/- 5%)

Answer 51

Bq-kBq up to 37 kBq. Crystal thickness and dead time are the primary factors determining minimum and maximum detectable activity The detection efficiency D (see Chapter 11, Section A) of the NaI(Tl) well counter for most γ-ray emitters is quite high, primarily because of their near 100% geometric efficiency g. The combination of high detection efficiency and low background counting levels makes the well counter highly suitable for counting samples containing very small quantities (Bq–kBq) of γ-ray-emitting activity. The geometric efficiency for small (environ 1-mL) samples in the standard well counter is approximately 93% (see Fig. 11-3). Because of their high intrinsic and geometric efficiencies (resulting from the use of a thick crystal and a well-type counting geometry, respectively), well counters are extremely sensitive and, in fact, can reliably be used only for counting activities up to approximately 37 kBq; at higher activities, dead-time counting losses become prohibitive and the measured counts inaccurate.

Answer 52

- Measure background before and after to have more reliable (mean) background? - Identify spills( “ Further, even trace contamination of the counting well will produce inaccurately high counting-rate values. Accordingly, a blank (i.e., an empty counting tube or vial) should always be included to determine the current background count.”)

Answer 53

D = ratio of detector counting rate to emission rate of a source = g x ε x f x F o g = geometric efficiency o For point source far away ~ Α/(4π r2) § A = area of detector § r = distance from point source o For point source close ~ ½ (1 – cos θ) o ε = intrinsic efficiency o f = fraction of output signals within PHA window o F = factor for absorption/scatter occurring within source or between source and detector Detector Efficiency: D = g x e x f x F Explain each term. g: geometric efficiency of the detector – efficiency with which detector intercepts radiation emitted from the source, determined mostly by detector size and distance from source. e: intrinsic efficiency with which detector absorbs incident photons and converts them to potentially usable detector output signal f: fraction of output signals produced by the detector recorded by the counting system, an important factor in energy-selective counting, when a pulse-height analyzer is used to select signals in a desired amplitude (energy) range F: Absorption and scatter within the source itself, or by material between source and detector

Answer 54

Intrinsic efficiency (ε) – efficiency with which detector absorbs incident radiation events and converts them into potentially usable detector output signal; determined by detector thickness and composition/density and by type and E of radiation – with increased E need increased crystal thickness o Decreases with increasing E o Increases with increasing thickness of detector o Increases as detector density and Z increase (stopping power)

Answer 55

``` Geometric efficiency decreases at a rate equivalent to the square of the distance o g = geometric efficiency o For point source far away ~ Α/(4π r2) § A = area of detector § r = distance from point source ```

Answer 56

“The coaxial Ge(Li) detector was developed in order to increase overall detector volume, and thus detection efficiency”

Answer 57

Tl doping (0.1-0.4 mol %) adds activation centres that makes NaI crystal an efficient scintillator at room temperature (vs. liquid nitrogen temperatures)

Answer 58

organic solvent – dissolves scintillator material (the primary solute) and radioactive sample; absorbs most radiation from sample and transfer energy to scintillator molecules primary solute (aka scintillator or fluor) – absorbs energy from solvent and emits light secondary solute (waveshifter) – absorb emissions from primary solute and re-emit photons of different wavelength which are better matched to PMT response additives – improve some aspect of LS performance, eg energy transfer efficiency from solvent to primary solute

Answer 59

a. Faster scan time (more scans performed in a day) b. Lower dose administered to the patient c. Better spatial resolution (improved images for more accurate diagnosis) d. Patient comfort (some scanners pt in sitting position and scan faster to acquire) e. Smaller size of the scanner – needs less room in hospital

Answer 60

The summed signal from all PMTs from a single scintillation event, which is then fed to the pulse-height analyzer for analysis.

Answer 61

``` Semiconductor High energy resolution Direct conversion to current Higher efficiency than gas-filled detectors Expensive Requires supercooling Poor stopping power ``` CZT Room temperature operation High Z, good stopping power ``` NaI Good stopping power 50-250 keV High light output Transparent to own scintillations Inexpensive Scintillation wavelength well matched to PMT ```

Answer 62

a) When kVP is increased from 120 to 140 – Increase, Non-linear b) When mAs is increased - Increase, Linear c) When pitch is increased from 1.0 to 1.5 – Decrease, Linear d) When collimation is increased from 1 to 5mm – Decrease, Linear

Answer 63

Photons = 1 Protons > 2 MeV = 5 Alpha/fission fragments = 20 Neutrons: i. <10keV = 5 ii. 10-100 keV = 10 iii. 100keV-2MeV = 20 iv. 2MeV-20MeV = 10 v. >20MeV = 5

Answer 64

● Absorbed dose D (Gy): energy absorbed per unit mass ● Equivalent dose (H, Sv): average absorbed dose of an organ that takes into account type and energy of radiation, according to weighting factor (wR). ● Effective dose (E, measured in Sv): a weighted total-body dose, considering the radiation type, organ sensitivity, and relative distribution of activity in vivo. Used in assessing potential for stochastic effects (Gy for deterministic effects).

Answer 65

Committed dose is a measure of the stochastic health risk (probability of cancer induction and genetic damage) due to an intake of radioactive material into human body. SI unit of measure is the sievert. Definition from Hall: Effective dose integrated over 50 years following intake of a radiopharmaceutical.

Answer 66

MIBI: Colon, Gallbladder Tetrofosmin: Gallbladder, Colon Thallium: Kidneys, Thyroid Isn’t there technically only 1 critical organ for a given radiopharmaceutical? The critical organ for Thallium are variable depending on where you look (ICRP, Requisites, Essentials, Kowalsky…)

Answer 67

a. Cumulated activity (Ã, Bq·s) = (amount of activity in a source organ) x (time the activity is present) b. Mean dose per cumulated activity (S; a.k.a. S-value, or dose factor, Gy/Bq·s): approximated constants for each organ pair, multiplied with cumulated activity to give an organ dose. It’s an approximation: i. D(rk ⃪ rh) = Ã x S(rk ⃪ rh)

Answer 68

In increasing dose: O15, N13, Rb82, Stress-only MIBI, One-day Stress-Rest MIBI, dual-isotope.

Answer 69

a. Effective dose and the tissue weighting factors are age- and sex-averaged, and do not actually change with patient age. Obviously, younger patients are more prone to negative effects of radiation, but this is not reflected in effective dose measurements; “radiation dose equivalent,” on the other hand, is an outdated term that provides tables of mSv/MBq for children of different ages, and of course younger patients have higher radiation dose equivalents. b. In111-WBCs, then Ga67, then Tc-WBCs (http://orise.orau.gov/files/reacts/pedose.pdf) c. Gotta be Ga67, considering its 78day halflife.

Answer 70

Linear energy transfer: the density of energy deposition along the particle’s path-length.

Answer 71

Dose and Dose-Rate Effectiveness Factor, which is the ratio between the radiation detriment from high doses/rates and that from low doses/rates.

Answer 72

a. Low dose rate causes less damage for most tissues (longer linear portion of the cell survival curve at lower doses)

Answer 73

a. Lots of double strand breaks, as well as SSBs, dicentric ring formations

Answer 74

Mechanisms: Scavenging of Free Radicals The sulfhydryl group may act by chemically reacting with free radicals generated by indirectly ionising radiation and preventing their interaction with DNA Improvement of DNA Repair The sulhydryl group may donate a hydrogen atom to assist in DNA repair pathways.

Answer 75

Hormesis: paradoxical, beneficial effect of low dose ionizing radiation in biological systems Data controversial, but typical effects <100 mSv Radiation hormesis is a theory that states that low level radiation (1-20 cGy acute dose of low LET radiation) can actually have a beneficial effect on health by stimulating the immune system.

Answer 76

Hormesis: paradoxical, beneficial effect of low dose ionizing radiation in biological systems There are three proposed mechanisms; o 1.DNA repair o 2.free radical detoxification o 3.stimulation of the immune system

Answer 77

``` Repair Redistribution (called reassortment in Hall) Reoxygenation Repopulation Radiosensitivity ```

Answer 78

Exposure to very low levels of radiation induces mechanisms whereby cells are better able to cope with subsequent higher levels of radiation exposure High frequency of mutations with the genome of a cellular lineage Dose to whole population required to double spontaneous mutation rate in population

Answer 79

- Direct action: radiation (typically high LET) interaction with DNA - Indirect action: radiation (typically low LET) interaction with other molecules (primarily H20), producing free radicals (H2O2 and OH), that cause DNA damage Indirect generally easier to repair, as usually constitutes single strand breaks (can lead to frameshifts and substitutions), while direct is more likely to cause double strand breaks (can lead to direct death from cytoxic effect of exposed dbl strands)

Answer 80

Stochastic effect: radiobiologic effect where probability of occurrence ↑ with radiation dose, but severity independent of dose; no threshold dose a. Example: cancer and heritable mutations Deterministic effect: radiobiologic effect with a threshold dose; severity ↑ with radiation dose b. Example: cataract and skin erythema

Answer 81

Stochastic effect: radiobiologic effect where 1. Probability of occurrence ↑ with radiation dose 2. Severity independent of dose 3. No threshold dose

Answer 82

Law of Bergonie-Tribondeau 1906: 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

Answer 83

Biological Effects of Ionizing Radiation Low LET radiation (x-rays, gammas), <100 mSv Most recent report involves “The primary objective of the study is to develop the best possible risk estimate for exposure to low-dose, low linear energy transfer (LET) radiation in human subjects.” Low dose = For this report, the committee has defined low dose as doses in the range of near zero up to about 100 mSv (0.1 Sv) of low-LET radiation.

Answer 84

Several including Japanese atomic bomb survivors (primary), Medical radiation studies, Occupational radiation studies, Environmental radiation studies

Answer 85

a. Medical Internal Radiation Dosimetry b. Biological Effects of Ionizing Radiations c. Dose and Dose-Rate Effectiveness Factor

Answer 86

a. Purpose: “BEIR VII develops the most up-to-date and comprehensive risk estimates for cancer and other health effects from exposure to low-level ionizing radiation.” b. Low-LET: “x-rays and gamma rays.” i. “low-LET radiation deposits less energy in the cell along the radiation path and is considered less destructive per radiation track.” ii. “The BEIR VII report defines low doses as those in the range of near zero up to about 100 mSv (0.1 Sv) of low-LET radiation.”

Answer 87

a. ”The most thoroughly studied individuals for the evaluation of health effects of ionizing radiation are the survivors of the Hiroshima and Nagasaki atomic bombings, a large population that includes all ages and both sexes. The Radiation Effects Research Foundation (RERF) in Japan has conducted followup studies on these survivors for more than 50 years.” b. “More than 60% of exposed survivors received a dose of radiation of less than 100 mSv (the definition of low dose used by the BEIR VII report).”

Answer 88

The principal effects of radiation on the developing embryo and fetus, aside from cancer, are embryonic, fetal, or neonatal death; congenital malformations; growth retardation; and functional impairment, such as mental retardation. Pre-Implantation (0 through 9 days), Organogenesis(10 days through 6 weeks), Fetal(6 weeks through term)

Answer 89

The radiation-induced bystander effect (bystander effect) is the phenomenon in which unirradiated cells exhibit irradiated effects as a result of signals received from nearby irradiated cells.

Answer 90

Oxygen enhancement ratio (OER) = ratio of dose under hypoxic to aerated conditions needed to achieve the same biological effect

Answer 91

- Hematopoietic 2.5-5 Gy (some symptoms may occur at 0.3 Gy) - Gastrointestinal ~ 10 Gy (some symptoms may occur at 6 Gy) - Cerebrovascular > 50 Gy (some symptoms may occur at 20 Gy)

Answer 92

Deterministic effect have a threshold; increasing dose leads to increased severity of effect; and the timing is within hours or days. Examples would include: radiation induced cataracts, skin radiation injury following fluoroscopy, cerebrovascular syndrome, sterility, etc.

Answer 93

LD50 /60 total body radiation ~ 3-4 Gy (with antibiotics and nursing this increases to 7 Gy, 100% lethality 10Gy) ``` Hematopoeitic syndrome ~ 2.5 to 5 Gy Death at 1-2 months GI syndrome > 10 Gy Death at 3-10 days Cerebrovascular syndrome 50-100 Gy Death at 24-48 hours ```

Answer 94

International Atomic Energy Agency The International Atomic Energy Agency is the world's central intergovernmental forum for scientific and technical co-operation in the nuclear field. It works for the safe, secure and peaceful uses of nuclear science and technology, contributing to international peace and security and the United Nations' Sustainable Development Goals.

Answer 95

It will produce Bremsstrahlung radiation, which is more penetrating in soft tissues A 0.5 lead apron will attenuate less than 15% of radiation for photon energies above 350 keV

Answer 96

MAG3 – Don`t I-123 >3 weeks FDG – Don`t

Answer 97

a) no interruption (DMSA, 111In-WBC) b) 12 hour interruption (MAA, 99mTc-HMPAO WBC, pertechnetate) c) 48 hour interruption (201 Tl) d) 3 week interruption (MIBG, 67-Ga) ALSO SEE NOTES

Answer 98

2 years Packaging and Transport of Nuclear Substances Regulations, 2015 (SOR/2015-145) Incorporation by reference of IAEA Regulations: For the purposes of these Regulations, the incorporation by reference of any particular amendment of the IAEA Regulations is effective two years after the day on which the amendment is initially published by the IAEA or six months after the day on which the amendment is available in both of the official languages of Canada, whichever is later.

Answer 99

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 A specific dose of radiation or other parameter that, if reached, may indicate a loss of control of part of a Permit Holder's radiation protection program, and triggers a requirement for specific action to be taken". The primary goal of the action to be taken is to prevent a re-occurrence of the events.

Answer 100

1. Conduct an 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.

Answer 101

a. “action level” means a specific dose of radiation or other parameter that, if reached, may indicate a loss of control of part of a licensee’s radiation protection program and triggers a requirement for specific action to be taken. b. When a licensee becomes aware that an action level referred to in the license has been reached, the licensee shall: i. conduct an investigation to establish the cause for reaching the action level; ii. identify and take action to restore the effectiveness of the radiation protection program iii. notify the CNSC within the period specified in the license

Answer 102

Minor Spill ● <100 exemption quantities Major Spill 1. >100 Exemption quantities 2. contamination of personnel 3. release of volatile substance

Answer 103

RSO Roles Annual review of the radiation safety program for adherence to ALARA Quarterly review of occupational exposures. Quarterly review of records of radiation level surveys. The RSO will schedule briefings and educational sessions to inform workers of ALARA programs. The RSO will ensure that authorized users, workers, and ancillary personnel who may be exposed to radiation will be instructed in the ALARA. An institution must establish Investigational Levels for occupational external radiation exposure which, when exceeded, will initiate review or an investigation into the over exposure of the worker or authorized user.

Answer 104

Side effects: - Thyroid storm - Sialoadenitis - Exacerbation of ophthalmopathy - Hypothyroidism (long term) - Neck tenderness Safety Issues - Separate bathroom - Flush immediately - Not primary child caregiver - Drive home separate from children if possible - Teratogenic (no pregnancy) - No breastfeeding

Answer 105

CNSC (Canadian Nuclear Safety Commission) – Nuclear Safety and Control Act (May 31, 2000)

Answer 106

The effective dose limits for a nuclear energy worker is set at 50 mSv in any one year and 100 mSv in five consecutive years. The dose limit for pregnant workers is 4 mSv from the time the pregnancy is declared to the end of the term.

Answer 107

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 (>1 mSv) 100 mSv over 5 years with a maximum of 50 mSv in any one year 1 mSv per year I think they are getting at that this is an action level. NEW probably requested to avoid further work while, the following take place:

Answer 108

a) What is the dose from natural radiation (for Canada)? Approx. 1.8 mSv (this is total natural background radiation) b) What is the dose from internal radiation (for Canada)? Approx. 1.2 mSv (ingestion + inhalation)

Answer 109

a. Natural background = 1.8mSv in Canada, 2.4mSv worldwide b. Ingestion = 0.3mSv c. Cosmic = 0.3mSv d. Terrestrial BG = 0.2mSv e. Inhalation = 0.9mSv

Answer 110

- Decay in storage - Release into sewer system (needs to be authorized explicitly in license) - Transfer to authorized recipient (e.g., landfill) - Incineration/atmospheric release

Answer 111

Dose rates in areas surrounding the room (therefore at the door) <2.5 μSv/h dose to other patients cannot exceed 0.5 mSv for their hospital stay can release when dose is < 7 mRem/h (<70 μSv/h) at 1 meter.

Answer 112

- After handling open-source radioiodine >2MBq, >200MBq in a fumehood, or >20,000 MBq in a glovebox (see table) - If exposed to a spill >2MBq - If externally contaminated - If working within 2m of a person whose screening results were >1kBq, within 1 hr of the suspected exposure CNSC reporting level is >=10kBq Screening must be performed 1-5 days from exposure

Answer 113

Other persons who regularly work close to a worker handling more than 2 MBq of volatile I-125 or I-131 on an open bench or in an open area should be screened for the relevant radioiodine. Workers and other persons who have been exposed to one of the following situations should be screened for the relevant radioiodine: 1. Exposed to a volatile I-125 or I-131 spill greater than 2 MBq; 2. Externally contaminated by I-125 or I-131; or 3. Worked within two meters of a person whose screening measurement results are equal to or greater than 1 kBq, if they were working within one hour after the time of the suspected exposure.

Answer 114

a. Limited quantity of radioactive material (below EQ threshold) (e.g. UN2910) b. Packaging that previously contained radioactive material. (e.g. UN2908)

Answer 115

TI = dose rate measurement at 1 meter in uSv/hr divided by 10 White I - maximum TI <0.05 Yellow II - 1.0 Yellow III - 10 SEE NOTES for exempted

Answer 116

a. at entry/access points to areas where there is an amount of radioactive substance > 100 EQs, or where there is a reasonable chance someone will be exposed to an effective dose rate >25 uSv/hr. Sign says “Rayonnement – Danger – Radiation”

Answer 117

BRCA 1 and 2 are tumor suppressor genes. BRCA1 protein is part of a complex that directly repairs DSBs by HRR; BRCA2 protein binds ssDNA (in DSBs) and initiates repair by HRR. VQ and CTPA important due to effects of radiation; patient with BRCA mutation less able to repair DSBs.

Answer 118

a. Valid b. Detector scatter c. Object scatter d. Septal penetration

Answer 119

Parallel hole, Pinhole, Converging, Diverging, Fan Beam

Answer 120

Better MTF is closer to 1.0 for all spatial frequencies. It is a measurement of the degradation produced by an imaging device as a function of various spatial frequencies. When M = 1 for A PARTICULAR SPATIAL FREQUENCY, this means no degradation of contrast for that frequency. Ideal imaging device has M=1 for all spatial frequencies. When M = 0 for a particular spatial frequency, the imaging device is unable to reproduce this particular spatial frequency. Therefore value of 0 = maximum degradation of spatial frequency. Calculated by FOURIER TRANSFORM of LSF or PSF.

Answer 121

MTFsystem = MTFintrinsic x MTFcollimator MTF is the FT of the LSF

Answer 122

Entrance window, photocathode, anode, dynodes, focusing grid, etc.

Answer 123

a. Relative dense with high atomic number, therefore good stopping power for 50-250 keV photons (photoelectric absorption) b. Efficient scintillator (1 visible photon/30 eV absorbed) c. Transparent to own scintillations d. Relatively inexpensive e. Scintillation light wavelength is well matched to PM tubes

Answer 124

a. Fragile b. Hygroscopic c. At higher γ energies Compton interaction dominates, requiring thicker crystal

Answer 125

a. Advantages: i. 1. Relatively dense (3.67 g/cc) with a high-Z atom (I, Z=53). Therefore, good absorber and very efficient detector of penetrating radiation in the 50 – 250 keV range. Predominant mode is photoelectric absorption ii. 2. Efficient, yielding 1 photon per 30 eV of energy absorbed iii. 3. Transparent to its own scintillations (approx 415 nm), even in large crystals iv. 4. Can be grown cheaply and in large size v. 5. Scintillation light well matched to peak response of PM tube cathode b. Disadvantages i. 1. Crystal fragile and easily fractured by mechanical or thermal stress (rapid temp changes). These create opacifications which reduce the amount of scintillation light reaching the photocathode. ii. 2. Hygroscopic. Exposure to moisture leads to yellow discoloration which impairs light transmission to the PM tube. Hermetic sealing required. iii. 3. At higher energies (> 250 keV), predominant interaction becomes Compton scattering, and larger volumes of NaI(Tl) are required for adequate detection efficiency.

Answer 126

“the period of time that a counter remains insensitive to count the next event after an event.” (Saha). Dead time reduces sensitivity, which reduces S/N ratio. Images are noisier due to dead time, but the spatial resolution is unchanged. Events that occur in the dead time are lost, and in paralyzable systems, extend the dead time even further.

Answer 127

Two-source method – This method is based on observing the count rate from two sources individually and then in combination. Because the losses are non linear, the observed rate due to the combined sources will be less than the sum of the rates from the individual measurements and the dead time can be obtained from this discrepancy. Fixed-rate pulser method – Fixed rate pulser connected to the preamplifier of the radiation detector. The pulser injects pulses of fixed amplitude (usually larger than the photopeak pulses of interest) into the circuitry, and the counting rate for these events is monitored using a separate single-channel analyzer window. The fractional loss of pulser events is equal to the fractional loss of radiation events because both are subject to same loss mechanisms

Answer 128

Extrinsic uniformity performed daily with sheet source directly on collimated detector. 10-15 million counts is acquired (Note: at my hospital 8 million counts for extrinsic and 15 million counts for intrinsic) g-Camera uniformity may be evaluated either intrinsically (i.e., without collimation) or extrinsically (i.e., with collimation). Intrinsically, a point source 0.1 mL in volume and containing 18.5 MBq of 99mTc is placed 5 crystal dimensions from and centered over the uncollimated detector to provide a near-uniform photon ﬂux impinging on the detector; if necessary, the activity should be adjusted to yield a measured counting rate of no greater than 25,000 cycles per second (cps), to avoid dead-time counting losses and counting-rate–related image degradation. Extrinsically, a uniform ﬂood, or sheet source (typically 185–555 MBq) of 57Co is placed directly on the collimated detector. A total of 10–15 million counts is acquired and uniformity quantitated for the integral and differential uniformities, which actually express the deviation from uniformity of the ﬂood image

Answer 129

● Intrinsic spatial resolution increases with: o Smaller crystal thickness o Higher photon yield o Higher energy photons (penetrate deeper into the crystal) o Decreased statistical variation in PMT response to scintillation light. ● Collimator resolution improve with: increasing septal depth, narrower holes, and putting the source closer to the collimator.

Answer 130

Septal depth, septal thickness, size of holes, material used (lead vs tungsten, vs ?), distance to object

Answer 131

Percent uncertainty = 100%/(square root N) 0.05=1/(square root N) N = 400 counts

Answer 132

``` MDA = 3√(R/t) Sorenson P138 (see Example 9-6) - MDA = activity of radionuclide that increases the counts recorded by an amount that is “statistically significant” compared to random variation. - MDA = 3 σ = 3 square root (Rb / t); Rb = background counting rate (cpm), t = counting time - First calculate in cpm, then divide by sensitivity (cpm/Bq) to get MDA in Bq ```

Answer 133

Use formula and then divide by the sensitivity of the counting device for the radionuclide question

Answer 134

Respiratory gating (4D PET) Low level free breathing Multiple breath holds (deep inspiration breath-holding technique (DIBH)) Post-processing algorithm: post-reconstruction registration and motion-compensated image reconstruction

Answer 135

Low level free breathing

Answer 136

1. Pressure Sensor – Belt around abdomen or thorax that detects pressure changes with respiration 2. Spirometry gating – measures airflow to and from lungs 3. Temperature sensor – similar to spirometer except detects temperature difference between air coming in and air leaving lungs. 4. Real-time position management respiratory gating - The RPM includes a video camera that measures respiratory motion by tracking the vertical displacement of 2 infrared reflective markers rigidly mounted on a plastic block placed on the patient’s thorax.

Answer 137

a. gamma is not parallel to the collimator and is not completely absorbed therein. Some of these gammas may still have enough energy to stay within the acceptance window. Increasingly important with high-energy emitters and thinner septa. b. 5%

Answer 138

· Septal penetration = proportion of the off-angle photons passing through lead septae of collimator and detected in adjacent portion of scintillator <5%

Answer 139

MTF is the modulus of the discrete Fourier transform of the measured line spread function Explanation from PDF In essence, both convey the same information: quantification of a system’s performance in capturing/transferring a signal/image. The MTF conveys this information as a frequency response to signals of varying frequencies. The LSF conveys this as the extent to which a single (sharp) line source is "blurred".

Answer 140

Term used for any operation that is applied to pixels in an image. It is a mathematical process by which images are suppressed in noise and also includes smoothing, edge enhancement and resolution recovery. The quality of SPECT images are degraded by several factors such as noise because of the limited number of counts, attenuation, or scatter of photons. Image filtering is necessary to compensate these effects and, therefore, to improve image quality. The goal of filtering in tomographic images is to suppress statistical noise and simultaneously to preserve spatial resolution and contrast.

Answer 141

Ramp filter – high pass filter that does not permit low frequencies that cause blurring to appear in the image. Eliminates the star artifact resulting from simple backprojection. Butterworth filter – low pass filter that smoothes noise while maintaining image resolution Metz filter – resolution recovery filter that is a function of the MTF of the gamma camera system Wiener filter – resolution recovery filter based on the signal to noise ratio of the specific image Hanning filter – relatively simple low pass filter that is very effective at reducing image noise but does not preserve edges Hamming filter – low pass filter that presents high degree of smoothing Parzen filter – low pass filter that is the most smoothing filter Shepp-Logan filter – low pass filter that is the least smoothing and has highest resolution

Answer 142

iteratively or filtered backprojection. The iterative reconstruction methods include algebraic methods like the algebraic reconstruction technique (ART) and statistical algorithms like maximum likelihood expectation maximization (MLEM) or ordered-subsets expectation maximization (OSEM) [1]. Filtered back-projection is used for image reconstruction. Back-projection alone (without filtering) results in undesirable image smoothing and the presence of star-like artifacts. The degree to which back-projection artifacts can be removed must be balanced by the degree to which image noise can be tolerated. Frequency refers to the change in number of counts from pixel to pixel. True image signal falls off rapidly with increasing frequency, while the noise content remains constant. Background (noise) is considered to be high frequency because there is marked variability in the number of counts from pixel to pixel. Image sharpness (edge detection, small objects, and fine detail) are also high frequency, while the target (a large object) is low frequency.

Answer 143

passive - named for its shape in the frequency domain - designed to reduce the star artifact resulting from backprojection - removes more data at the low end of the spectrum (a type of high-pass filter) - Accentuate edges and retain finer details but create a “grainy” appearance because of high-frequency noise that makes the images difficult to interpret - High pass filters are limited to the ramp filter in nuclear medicine

Answer 144

- used to reduce the contribution of high-frequency noise and smoothes the image - results in an image with indistinct edges and loss of detail - Examples: Hann, Hanning, Butterworth, Parzen

Answer 145

active - Composed of two parts: inverse MTF, roll-off for high frequencies - Take into account system characteristics, statistics of the image, statistical noise in the data - Provides both amplification and attenuation of frequencies in selected ranges…. So ideally, tries to reduce noise without unduly penalizing resolution - Examples: Metz, Wiener

Answer 146

- the prefilter (eg. Butterworth, hann, hamming, parzen, etc) and ramp filter are applied in a single step. - Example: Ramp-Parzen

Answer 147

a. Filtered Backprojection, Ordered Subsets Expectation-Maximization b. OSEM is faster than MLEM; IR produces less streak artifact than FBP and FT; IR creates more accurate reconstructions than FBP/FT. ``` OSEM vs MLEM Smaller # of projections Faster Processing time Less noise Smoother solution ``` MLEM vs. MAP MLEM at high iterations emphasizes noise, but there is guaranteed convergence MAP produces smoother solution, converges faster, but computationally difficult MLEM = maximum likelihood expectation maximization - uses Poisson statistics to compute the most likely source distribution that would have created the observed projection data. It biases heavily towards the high count data, as well as the high spatial frequency data, therefore an increased number of iterations lead to increased noise. OSEM = Ordered-Subsets Expectation Maximization - considers only a subset of project data in each iteration, speeding up the reconstruction MAP = maximum a posteriori - uses knowledge based on the prior iteration to enforce smoothing, hence reducing noise ``` OSEM better than MLEM: - reconstruction is faster MLEM disadvantage: - slow to converge - as the number of iteration ↑, noise tends ↑ too (compared to MAP), biasing the image heavily towards the higher spatial frequencies. ```

Answer 148

Integral uniformity is based on the maximum and minimum pixel counts in the image. This is calculated for the UFOV and CFOV. Integral uniformity values are typically 2% to 4% for planar images, and need to be ~1% for SPECT to be artifact-free.

Answer 149

a. Center of rotation testing. b. Tomographic uniformity. c. Multihead cameras need to be aligned together.

Answer 150

a. Photopeak and uniformity (for Tc99m) daily. b. Spatial resolution and COR alignment weekly. c. Uniformity (for other nuclides), tomographic uniformity, overall SPECT performance monthly or quarterly.

Answer 151

a. In-plane resolution (a.k.a. transaxial resolution): determined by collimator resolution (dominant factor), intrinsic resolution of the camera, angular and linear sampling intervals, and properties of the reconstruction filter. b. Axial resolution (a.k.a. slice thickness): determined by collimator resolution (dominant factor), intrinsic resolution of the camera, and the interval along the Z-axis.

Answer 152

a. Qualitatively in planar: look at bar phantom, and spatial resolution is equivalent to the smallest quadrant you can still visually distinguish the lines from one another. Not sure how this is done in SPECT. b. Quantitatively for SPECT: Scan a tiny point source (<25% the FWHM of the camera) or line sources at multiple locations through the UFOV. FWHM of the PSF (or LSF for line sources) is obtained at each location. Transaxial spatial resolution is the average x- and y-plane FWHMs, and axial resolution is the average z-axis FWHM. MTF is a better measure because it accounts for the shape of the PSF (PSFs of different shapes can have the same FWHM), and can be acquired as the FT of the PSF. c. Quantitatively for planar, use the bar phantom method.

Answer 153

Decay Method exposing an uncollimated detector to a radioactive source (typically Tc-99m) and sampling the count rate at intervals over a period of time sufficient such that radioactive decay results in low observed count rates where losses are negligible. Dual Source Method making count rate measurements using two sources of similar activity, with the detector exposed to each source individually and then concurrently these measurements must be corrected for background. Once these measurements are made, τmay be estimated based on the following equation:

Answer 154

improper patient positioning, respiratory motion, other voluntary patient movement, or mechanical misalignment of the SPECT/CT device

Answer 155

A more recent study, by Fricke et al. (3), suggested that a misalignment of 1 pixel can lead to artifacts in the anterior, apical, and septal segments.

Answer 156

CT truncation artifact Beam hardening Partial volume averaging

Answer 157

· Respiratory motion · Sag of emission table · Patient motion between acquisitions

Answer 158

Absorption of low-energy x-rays from a polyenergetic beam, results in streak artifact at high-density high-Z areas. Corrected by using adaptive tube current modulation, which varies the kvp and mas in different areas of the patient.

Answer 159

``` · SUV = 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 ```

Answer 160

Size Metabolic activity of the nodule Respiratory motion

Answer 161

- Dose of FDG - Interstitial injection - Uptake period - Reconstruction matrix size, algorithm and filtering - Size of ROI - Attenuation correction ALSO SEE NOTES

Answer 162

Blank scans - performed daily by uniformly irradiating the detector elements using either the 68Ge or 137Cs transmission source (if applicable) of the scanner without any source or other attenuating object in the ﬁeld of view (FOV) or with a uniform source of 511-keV annihilation photons (most commonly a 20-cm-diameter 68Ge cylinder) centered in the FOV. The term blank scan, derived from the ﬁrst of these 2 approaches, reﬂects the absence of any material in the FOV; the term is still often applied to the latter approach, even though it involves placing an object (i.e., the 68Ge source) in the FOV. For PET systems that use 68Ge or 137Cs transmission data to derive attenuation corrections, the blank scan also provides the reference (i.e., unattenuated) transmission data for calculating such corrections. In some respects, the blank scanner is analogous to the daily uniformity ﬂood image acquired for g-cameras, providing an overall assessment of detector response.

Answer 163

Blank or hypointense diagonal line or band on a sinogram indicate that a detector element or detector block is malfunctioning.

Answer 164

Tomographic uniformity - for PET is essentially the same as that for SPECT and may be evaluated with either a 18F-ﬁlled cylinder phantom or a 68Ge cylinder source. In practice, the use of a long-lived 68Ge cylinder is preferred because constant reﬁlling of a cylinder with shortlived 18F is avoided. Tomographic uniformity should be evaluated daily or at least weekly Normalization scan - Nonuniform response can be corrected by acquiring data for a uniform ﬂux of annihilation g-rays ). Such a scan is known as a normalization scan and the uniformity correction thus derived (analogous to the uniformity correction table of a g-camera) is known as a normalization. SEE NOTES

Answer 165

RC = Measured peak activity concentration / true activity concentration Used to correct for partial volume effect in PET/CT Linear sampling interval sets voxel size Too small voxel - low counting statistics/voxel and ↑ noise Too large voxel - partial volume averaging

Answer 166

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

Answer 167

BaF2 used in the past; LSO/LYSO used in existing scanners; LaBr3 being tested

Answer 168

Short rise and decay time High light output Good stopping power for 511 keV photons

Answer 169

a. by determining the time difference between photons, we can calculate the relative distance between the 2 detectors from which the annihilation event occurred. b. Improves PET by increasing image quality, allowing for shorter scan times and/or lower dose, higher spatial resolution, lower sensitivity to inconsistent data, and the opportunity for new architectures with missing angles.

Answer 170

Resolution = √((Rrange)2 + (Rdetector)2 + (Rnon-colinear)2

Answer 171

Annihilation photons are not exactly 180 degrees apart because of the residual kinetic energies of the positron and negative electron. Results in 2 – 3 mm loss of resolution. Loss of resolution is a function of distance between the detectors.

Answer 172

Non-colinearity: R180° = 0.0022 x D = 0.176 cm = 1.76 mm

Answer 173

True coincidence, linearly proportional to activity Scatter coincidence, linearly proportional to activity Random coincidence, proportional to activity squared

Answer 174

I wonder if they asked for 2 and not 3… In the past they have asked for 2, and Sorenson only describes 2. o Delayed window method o Singles method To correct random coincidence: 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 Singles method - If the rate at which single (not coincidence) events occur in each detector is measured, and the coincidence timing window ΔT is known, then the rate of random coincidences for any pair of detectors can be computed

Answer 175

a. In blood, it’s in equilibrium between NH3 and NH4+. b. Gets into cell by passive diffusion (as NH3) c. Converted to N13-glutamine by enzyme glutamine synthetase, and trapped in there as an amino acid

Answer 176

a. H2O is freely diffusible, b. 100% extraction by myocardium c. Not affected by metabolic factors d. Unlike other agents, extraction is linear even at high flow rates e. Can perform quantitative regional blood flow measurements of myocardium. f. Disadvantages: i. Image quality is inferior (high blood pool activity) ii. Short half-life, etc.

Answer 177

The purpose is to reduce amount of scatter that is accepted. The sensitivity is higher for 3D than for 2D.

Answer 178

True, scatter, random. True and Scatter events increase linearly with activity; random events increase with the square of activity. To decrease random events: use 2D imaging with septa, reduce dose, scatter correction (delayed window method or singles method), reduce coincidence acceptance window.

Answer 179

- Mean: sum of values divided by number of values - 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)

Answer 180

Prevalence: number of cases of a disease existing in a population at a certain moment in time Incidence: number of new cases of a disease occurring in a population within a specified period of time

Answer 181

Prevalence = incidence x length of disease

Answer 182

a. Prevalence = incidence x length of disease, so length of disease = Prevalence/incidence = (1/100)/(30/100,000) = 0.01/0.0003 = 33.3 years

Answer 183

· Continuous data can have any value within a certain range o Weight o Height

Answer 184

a) A way to analyze the accuracy of a test and to determine the best threshold value for distinguishing between positive and negative test results. The area under the curve is the accuracy of the test. Accuracy is measured by the area under the ROC curve. o 1 – excellent o 0.5 – worthless b) TP fraction (Sn) (y axis) vs. FP fraction (1-Sp) (x axis)

Answer 185

Respect for Persons ● In practice, this means that individuals have a right to decide for themselves whether to participate in research. You may not use information about people without first getting their informed consent. Special care must be taken with people who are unable to understand or who are particularly susceptible to coercion. Beneficence ● This means that it is not OK to use people for research unless the research is likely to have some benefit. Furthermore, this benefit must outweigh the risks. Justice ● Justice requires that people be treated fairly. Researchers should not take from research participants without giving back:

Answer 186

ICER is the ratio of the change in costs to incremental benefits of a therapeutic intervention or treatment. The equation for ICER is: ICER = (C1 – C2) / (E1 – E2) where C1 and E1 are the cost and effect in the intervention or treatment group and where C2 and E2 are the cost and effect in the control care group. Costs are usually described in monetary units while benefits/effect in health status is measured in terms of quality-adjusted life years (QALYs) gained or lost.

Answer 187

the probability of event A (e.g., having breast cancer) given event B (having a positive mammogram) depends not only on the relationship between A and B (i.e., the accuracy of mammograms) but on the absolute probability (occurrence) of A not concerning B (i.e., the incidence of breast cancer in general), and the absolute probability of B not concerning A (i.e. the probability of a positive mammogram). crucial point to remember from Bayes’ theorem is that the prior probability (or pretest clinical assessment) is as important as the sensitivity and specificity of the diagnostic test in the determination of the post-test probability (the probability that the patient with a positive test truly has the disease).

Answer 188

a. The probability of falsely rejecting the null hypothesis (due to inadvertently sampling outliers, for example), when the null hypothesis is in fact true. b. Too low

Answer 189

In sentence form, positive likelihood ratio is “the probability of a person who has the disease testing positive divided by the probability of a person who does not have the disease testing positive.” LR+ = Sn / (1-Sp)

Physics/Radiopharm Flashcards

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