Nuclear Medicine (Erin) Flashcards
(185 cards)
1
Q
What is the energy of gamma emission released from Tcm99?
A
140keV
2
Q
What is the most common type of gamma camera?
A
Parallel
3
Q
How does half life change with temperature?
A
It doesn’t
Half life of isotope is fixed
4
Q
What is the half life of Tc99
A
200,000 years
5
Q
What is the half life of Tcm99
A
6 hours
6
Q
What is the half life of Iodine 123
A
13 hours
7
Q
What is the half life of Iodine 131
A
8 days
8
Q
What is the half life of Fluorine-18
A
110 min
9
Q
How is effective half life calculated
A
1/effective half life
= 1/biological half life + 1/physical half life
10
Q
In NM:
Which type of collimator is used to image the thyroid?
A
Pin hole collimator
11
Q
In NM:
Which type of collimator gives a magnified view?
A
Converging collimator
12
Q
In NM:
Which type of collimator gives a minified view?
A
Diverging collimator
13
Q
In NM:
What is the crystal in a gamma camera made from?
A
Single crystal of sodium iodide dopes with thallium
14
Q
Does a broad photopeak with a large full width half maximum (FWHM) demonstrate an efficient or inefficient system?
A
Inefficient
15
Q
How do PET isotopes decay?
A
By positron emission
16
Q
Describe positron emission
A
Proton heavy nucleus converts proton to neutron
Released position
The positron usually combines with an electron somewhere (annihilation) to release a pair of gamma rays
17
Q
What happens to the atomic number in positron emission?
A
Decreases by 1
18
Q
What happens to the mass number in positron emission?
A
Stays the same
19
Q
What type of radiation does Tc99m release?
A
140keV Gamma radiation is release via Isomeric transition
20
Q
What is the half life of Mo99?
A
66 hours
21
Q
Describe beta negative decay
A
Neutron rich nucleus
Converts neutron to proton
Releasing electron and uncharged antineutrino
22
Q
What happens to the atomic number in beta decay?
A
Increases by 1
23
Q
What happens to the mass number in beta decay?
A
Unchanged
24
Q
Describe isomeric transition
A
Following radioactive decay daughter nucleus can be left in excited state
Can remain in this excited state for a period of time before emitting excess energy as gamma ray
25
What happens to the atomic and mass number during isomeric transition?
Nothing
Remains the same
26
Describe internal conversion
Instead of gamma emission
Excited radionuclide transferred energy to inner shell electron which is then emitted with high energy
Characteristic xrays then produced from rearrangement of electrons
27
What types of scintillation crystal is used in PET?
Bismuth germanate (BGO)
lutetium oxyorthosilicate (LSO)
gadolinium oxyorthosilicate (GSO)
28
What is the MOST COMMON type of scintillation used in PET?
Bismuth germanate (BGO)
29
What energy of gamma rays are emitted during annihilation?
511keV
29
Does reduced patient to camera distance improve or worsen spatial resolution?
Improves
30
Does increased patient to camera distance improve or reduce spatial resolution?
Reduces
31
What is the effect of increasing collimator hole length on SR
Improves SR
32
What is the effect of reducing collimator hole length on SR
Reduced SR
33
What is the effect of increasing collimator hole length on collimator sensitivity?
Reduces sensitivity
34
What is the effect of decreasing collimator hole length on collimator sensitivity?
Increases sensitivity
35
What is the effect of decreasing hole diameter on SR?
Improves SR
36
What is the Effect of increasing collimator hole diameter on SR?
Reduced SR
37
What is the effect of increasing collimator hole diameter on collimator sensitivity?
Increases sensitivity
38
What is the effect of decreasing collimator hole diameter on collimator sensitivity?
Decreases sensitivity
39
What is the typical spatial resolution in nuclear medicine images?
10 FWHM mm
(0.05lp/mm)
40
What controls contrast in NM imaging
Mainly controlled by relative uptake of the tracer in different tissues within the patient
41
Does scatter in NM improve or reduce contrast?
Scatter reduces contrast
42
How does PHA affect contrast/scatter when narrow/wide?
Narrower PHA rejects more scatter and improves contrast
Wider PHA accepts more scatter and recduces contrast
43
What is the typical PHA window width
Typically 15-20% of the photopeak
44
What is the effect of a lower resolution collimator on noise
Reduces noise
As allows more gamma rays to be detected
44
What is the effect of longer acquisition time on noise?
Reduces noise
As allows more gamma rays to be detected
But lower SR
45
What is the effect of increased injected activity on noise?
Reduces noise
As allows more gamma rays to be detected
45
What is the effect of shorter acquisition times on noise?
Increases noise
Less time for gamma rays to be detected - less gamma rays detected
46
What is the effect of a higher resolution collimator on noise
Increases noise
Less gamma rays detected
But higher SR
47
What is the effect of decreased injected activity on noise?
More noise as less gamma rays detected
48
How does Gallium-67 decay?
electron capture
It has too few neutrons
49
How does Technetium 99m decay?
Via gamma emission
50
How does Iodine-131 decay
via beta emission
51
How does Fluorine-18 decay
By positron emittion
52
How does Mo99 decay to 99mTc
By beta emission
53
What type of atom is emitted during alpha decay
Helium atom
54
What happens to the atomic number in alpha decay
Decreases by 2
55
What happens to the mass number in alpha decay
Decreases by 4
56
How long is a technetium generator useful for?
5 days
57
What does 99TC decay to?
99Ru
58
Why is Iodine 131 unstable and therefore how does it decay?
Has too m any neutrons
Decays via beta emission
59
Why is Fluorine-18 unstable and how does it therefore decay?
Has too many protons (too few neutrons)
Do decays via positron emission
60
Why is Mo99 unstable and therefore how does it decay?
It has too many neutrons
Decays via beta emission
61
What is the effect of higher energy gamma ray emission on patient dose?
Decreases patient does as less interaction/absorption in patient tissues
62
What is the effect of a short effective half life on patient dose?
When Teff is short, activity rapidly disappears from the body and the effective dose is lower
63
Does the radiosensitive weighting of tissues targeted by the radionuclide in NM affect patient dose?
Yes
Tissues targeted that have a higher tissue weighting factor will experiences an increased effective dose
64
Does an increase administered activity increase or decrease dose?
Increases dose
65
What is the effect of a high cut of frequency filter in filtered back projection?
Sharper features (better SR)
Higher noise
66
What is the effect of a low cut of frequency filter in filtered back projection on SR and noise?
Smoother features (worse SR)
Lower noise
67
What does OSEM stand for? What is it?
Ordered subset expectation maximisation
The most common reconstruction algorithm for PET images
68
Does the collimator in nuclear imaging reject scatter
NO
69
What is the role of dynodes in a PMT?
Held at increasingly positive potential to each other
Electrons accelerated towards them
Electron accelerated by potential differences and gain kinetic energy
Also generate new electrons
ELECTRON AMPLIFIER
70
How do PET isotopes decay?
Via positron emission
71
What is the effect of a smaller FWHM (full width half maximum) on SR
Improves SR
72
What is the effect of a larger FWHM (full width half maximum) on SR?
Reduces SR
73
What is the effect of a high resolution collimator in SPECT on SR?
Improves SR
74
What is the effect of a low resolution collimator in SPECT on SR?
Reduces SR
75
What is the effect of acquiring a larger number of projections in SPECT on SR?
Improves SR
76
What is the effect of acquiring a lower number of projections in SPECT on SR?
Reduces SR
77
What is the typical spatial resolution in SPECT (in FWHM)
10-15mm FWHM
78
What is the effect of iterative reconstruction on attenuation and scatter in SPECT?
Provides attenuation correction and attenuation correct
Improving contrast
79
What types of artefact can camera non uniformity cause in SPECT?
Ring artefacts
80
How is attenuation variation typically corrected for in SPECT?
By using a low dose CT
81
Name some examples of positron nuclides used in PET scanning
F18
C11
N13
82
In PET what is the line between the detectors called?
Line of response
83
In PET what is a true coincidence
When both 511keV gamma rays from a single annihilation event interact with a pair of detectors without prior scattering in the patient
83
In PET:
What happens to the number of random events compared to true events when activity administered to patient increases
The number of random events increases much faster than the number of true events
84
In PET:
What is a random coincidence?
When two gamma rays interact with a pair of detectors but each gamma ray has come from a different annihilation event
Line of response does not correspond to the position of either of the two annihilations
85
In PET:
What is a scatter coincidence?
Occurs when one/or both of the gamma rays from a single annihilation event undergoes compton scatter interaction in the patient before being detected
Line of respond does not correspond to the position of the annihilation
86
Is NaI crystal used in PET scanners
No
87
Why are BGO or LSO crystals used in PET scanning rather than NaI (like is used in planar)
Because BGO and LSO are better than NaI for detection of 511keV gamma rays
88
What is the SR of PET scans at the centre?
4mm FWHM
89
What is the SR of PET scants at the periphery
5mm FWHM
90
What 3 factors affect SR in PET?
Distance travelled by positron before annihilation
Non-colinearity
Size of individual detectors
91
What is non-colinearity in PET?
What effect does this have?
2 annihilation gamma rays are not emitted at exactly 180 degrees to each other
Causes blurring with increases with the radius of the PET detector ring
92
Is the SR of a PET scanner better at the centre of periphery of the detector?
SR of a PET scanner is best at the centre of the image and degrades towards the periphery
93
Why types of scintillators are used for TOF PET
LSO or LYSO
94
What is the purpose of time of flight PET
used to improve the accuracy of the reconstruction
As measures the time difference between the arrival of the gammas
95
Does TOF PET improve or reduce SR
Improves SR
96
Is the demand for FDG greater in normal tissue or tumour tissue
Tumour tissue
97
What is the adult dose of 18FDG (in MBq/kg)
3MBq/kg
98
What is the effective dose from 18FDG administration
5-8mSv
99
What are the typical administered activities in 18FDG studies (MBq) for an adult?
200-350 MBq
100
What is the typical study time for FDG18 scans
20 minutes
101
What causes a cold artifact in PET scanning
Created due to different patterns of breathing between the (much shorted) CT scan and the longer PET scan
102
What can help reduce the effect of cold artefact
Asking the patient to use shallow breathing
103
What does SUV stand for
Standard Uptake Value
104
What is SUV the ratio of
FDG concentration in tissue: to injected activity per kg of the patient
105
What can SUV be used to differentiate between
Benign and malignant lesions
And assess treatment response
106
What is the rough cut off in SUV between malignant and benign lesions
2.5
107
What factors can affect SUV (5)
Corrections applied to the PET data
Method of image reconstruction
Region of interest selected
Delay between injection and scan
Lean vs total body mass patient
108
Is the SR in PET or SPECT better
PET
109
In PET:
What is the effect of longer acquisition times per bed position on image noise
Longer times reduce noise
110
A MAG3 scan is dynamic or static?
Dynamic
111
T/F - A DTPA scan is safe in patients with renal failure?
False. DTPA is cleared via glomeruli.
112
DMSA scan is static or dynamic?
Static
113
Kidney Imaging - what are DMSA, DTPA and MAg3 used for?
DMSA - Kidney cortex
DTPA - eGFR
MAG3 - renal plasma flow
114
What is SPECT?
3D version of planar, takes 30mins and uses multiple cameras and the images taken are overlaid.
115
What is the effect of a high resolution collimator on SPECT image quality?
Improved SR
116
What is the effect of acquiring a larger number of projections on SR in SPECT?
Improved SR
117
What is the effect of using a high cut off filter during reconstruction on SR in SPECT?
Improved SR
118
Why are SPECT images noisy? (3)
High resolution collimators
Limited time per projection
Mean low number of detected gamma rays
119
What type of artefacts does camera non-uniformity cause in SPECT?
Ring artefacts
120
How is CT used in SPECT imaging?
To correct SPECT images for attenuation (Attenuation correction)
Provided using low dose CT scan
121
In PET imaging:
What happens to the number of random events (compared to the number of true events) as the activity administered increased?
The number of random events increases much faster to the number of true events
122
In gamma imaging does the collimator reject scatter?
No
123
In gamma imaging:
What is the role of the pulse height analyser window on image contrast?
Attempts to reject scatter
To improve image contrast
124
In NM imaging how does a lower resolution collimator affect noise?
Reduced noise as more gamma rays accepted
However this reduces SR
125
In NM how does longer acquisition time affect random noise?
Reduces noise
(however more change of motion artefact)
126
In NM how does increased injected activity affect random noise?
Reduced noise
(however higher patient dose)
127
In NM:
How does administered activity affect patient dose?
More injected activity
Higher patient dose
128
In NM:
How does the energy of emitted gamma rays affect patient dose?
Higher the energy of gamma rays the less the patient dose
As higher energy gamma rays experience fewer interactions and less absorption in tissue
Therefore the dose will be less
129
In NM:
How does the bio-distribution of the pharmaceutical affect patient dose?
If the tracer is taken up but radiosensitive organs (i.e those with a high tissue weighting factor)
Then the effective dose (measured in Sv) will be increased
130
In NM:
How does the effective half life of radionuclide affect patient dose?
When half life is short - rapidly disappears from the body and the effective dose will be lower
131
What is the effective dose from FDG18 administration
5-8mSv
132
What is the effective dose from initial (low dose) CT in 18FDG scans
4-6mSv
133
Is a collimator required for PET scanning?
No
Relies on coincidence detection
134
What is the spatial resolution in PET imaging?
FWHM of 4-5mm
(0.2 lp/mm)
135
What does spatial resolution depend on in PET scanning (3)
Coincidence detection
Size of detectors and radius of detector ring
Choice of filter during reconstruction
136
Are NaI detectors used in PET scanning?
No
137
How is fluorine 18 (FDG) used in PET scanning produced?
In a cyclotron
by bombarding 18-Oxygen with protons
138
How does a cyclotron produce raidonuclides?
By bombarding stable nuclei with highly energetic charged particles (typically protons)
Forcing neutrons out of the nucleus
139
What are the two methods by which nuclear reactors create radionuclides?
Extraction of fission products
Production by neutron activation
140
What is the disadvantage of nuclear reactors?
Relatively low yield of the desired radioisotope and the substantial production of other radioisotopes
141
What are common radioisotopes produced in a nuclear reactor?
Mo 99 (by neutron bombardment)
131 I (by fission)
142
What is the septal thickness, max keV, and radionuclide used for low energy collimators?
Thickness = 0.3mm
Max keV = 150
Radionuclide = 99mTc
143
What is the septal thickness, max keV, and radionuclide used for medium energy collimators?
Thickness =1mm
Max keV = 300
Radionuclide Indium -111
144
What is the septal thickness, max keV, and radionuclide used for high energy collimators?
Thickness =2mm
Max keV = 400
Radionuclide - Iodine 131
145
How thick are the scintillation crystals in gamma cameras?
About 10mm
146
Name 3 examples of static planar imaging
DMSA renal scan
Bone scan
Lung perfusion scan
147
Name 3 examples od dynamic planar imaging
MAG3 renal scan
Gallbladder emptying scan
Gastric emptying scan
148
When is gated imaging used in planar imaging?
When study organs have regular physiological motion
e.g cardiac imaging
149
What is the typical matrix size for static imaging
256x256
150
What is the typical matrix size for dynamic imaging?
128x128
or
256x256
151
What is the typical matrix size for gated cardiac imaging
64 x 64
152
What material are collimators typically made of
Lead
153
Why are collimators typically made of lead
Due to high linear attenuation co-efficient
154
Which has a thicker septa? Collimator used for 99Tcm imaging or collimator used for 131 Iodine imaging?
131 Iodine (keV = 364)
Note keV for 99Tcm = 140
155
What happens if the septa in the collimator is too thin for the radionuclide used?
Increased probability of penetration by gamma photons that are not travelling parallel to the axes of the hole
Called septal penetration
156
What is the result of septal penetration on image quality
Reduced image quality
157
How many photomultiplier tubes are in a typical gamma camera
30-100
158
159
What percentage of TC99m decays via internal conversion?
10%
90% is via isomeric transition
160
What is electron capture?
Radioactive decay method
Proton rich nucleus captures a K shell electron to neutralise its positivity
Rearranging of the electron shells emits characteristic X-rays
161
What is the decay constant?
The fraction of all the radioactive atoms in a sample that are disintegrating each second
Substance dependent
162
How do you extract TC99m from a molybdenum technetium generator?
Pass saline through the molybdenum source
163
What is the optimum time interval of extracting technetium from the generator?
23 hours
164
What is the PHA for Technetium 99m?
Window is 126-154 keV
165
In nuclear medicine does the Collimator reject scatter?
No it has no role in scatter rejection in nuclear medicine
166
How to increase spatial resolution in nuclear medicine studies? (3)
1. Decrease patient to camera distance
2. Increase collimator resolution
3. Decrease patient motion
167
Typical spatial resolution in nuclear medicine studies?
0.05 line pairs per mm
168
How to increase contrast in Nuclear medicine studies?
Narrower Pulse height analyser window to reject more scatter
169
How to reduce noise in nuclear medicine studies? (3)
1. Use a lower resolution collimator
2. Longer acquisition times
3. Increase injected activity
170
What 2 general factors affect patient dose from a radionuclide?
1. Increase number of disintegrations in patient
2. Energy deposition per disintegration
171
How is spatial resolution in SPECT affected by resolution of collimator?
High resolution collimator gives high spatial resolution
172
How to reduce Noise in Spect? (3)
1. Inject more activity of radionuclide
2. Choice of reconstruction filter
3. Use resolution recovery reconstruction
173
How to reduce noise in PET? (2)
- 3D acquisition
- longer acquisition time per bed position
174
Alpha radiation vs Beta emission
Which is more strongly ionising?
Which is more penetrating?
Alpha is more strongly ionising
Beta is more penetrating
175
The main artefact with back projection is …? Which occurs around which areas?
Star/streak artefact
Hot areas
176
Isotopes share chemical properties or physical properties?
Only share chemical properties
177
Tc99 decays by…?
Beta emission
178
SPECT: How is spatial resolution affected by large number of projections?
Improves resolution
179
SPECT: How is spatial resolution affected by a high cut-off filter during reconstruction?
Improves resolution
180
SPECT: How is spatial resolution affected by circular orbits?
Reduced resolution
Non-circular is better for resolution
181
True or false: Radionuclides decay exponentially
True
