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Nuclear Medicine (Erin) Flashcards

1
Q

What is the energy of gamma emission released from Tcm99?

A

140keV

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2
Q

What is the most common type of gamma camera?

A

Parallel

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3
Q

How does half life change with temperature?

A

It doesn’t
Half life of isotope is fixed

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4
Q

What is the half life of Tc99

A

200,000 years

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5
Q

What is the half life of Tcm99

A

6 hours

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6
Q

What is the half life of Iodine 123

A

13 hours

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7
Q

What is the half life of Iodine 131

A

8 days

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8
Q

What is the half life of Fluorine-18

A

110 min

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9
Q

How is effective half life calculated

A

1/effective half life
= 1/biological half life + 1/physical half life

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10
Q

In NM:
Which type of collimator is used to image the thyroid?

A

Pin hole collimator

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11
Q

In NM:
Which type of collimator gives a magnified view?

A

Converging collimator

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12
Q

In NM:
Which type of collimator gives a minified view?

A

Diverging collimator

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13
Q

In NM:
What is the crystal in a gamma camera made from?

A

Single crystal of sodium iodide dopes with thallium

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14
Q

Does a broad photopeak with a large full width half maximum (FWHM) demonstrate an efficient or inefficient system?

A

Inefficient

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15
Q

How do PET isotopes decay?

A

By positron emission

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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

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17
Q

What happens to the atomic number in positron emission?

A

Decreases by 1

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18
Q

What happens to the mass number in positron emission?

A

Stays the same

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19
Q

What type of radiation does Tc99m release?

A

140keV Gamma radiation is release via Isomeric transition

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20
Q

What is the half life of Mo99?

A

66 hours

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21
Q

Describe beta negative decay

A

Neutron rich nucleus
Converts neutron to proton
Releasing electron and uncharged antineutrino

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22
Q

What happens to the atomic number in beta decay?

A

Increases by 1

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23
Q

What happens to the mass number in beta decay?

A

Unchanged

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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

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25
Q

What happens to the atomic and mass number during isomeric transition?

A

Nothing
Remains the same

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26
Q

Describe internal conversion

A

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

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27
Q

What types of scintillation crystal is used in PET?

A

Bismuth germanate (BGO)
lutetium oxyorthosilicate (LSO)
gadolinium oxyorthosilicate (GSO)

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28
Q

What is the MOST COMMON type of scintillation used in PET?

A

Bismuth germanate (BGO)

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29
Q

What energy of gamma rays are emitted during annihilation?

A

511keV

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29
Q

Does reduced patient to camera distance improve or worsen spatial resolution?

A

Improves

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30
Q

Does increased patient to camera distance improve or reduce spatial resolution?

A

Reduces

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31
Q

What is the effect of increasing collimator hole length on SR

A

Improves SR

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32
Q

What is the effect of reducing collimator hole length on SR

A

Reduced SR

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33
Q

What is the effect of increasing collimator hole length on collimator sensitivity?

A

Reduces sensitivity

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34
Q

What is the effect of decreasing collimator hole length on collimator sensitivity?

A

Increases sensitivity

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35
Q

What is the effect of decreasing hole diameter on SR?

A

Improves SR

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36
Q

What is the Effect of increasing collimator hole diameter on SR?

A

Reduced SR

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37
Q

What is the effect of increasing collimator hole diameter on collimator sensitivity?

A

Increases sensitivity

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38
Q

What is the effect of decreasing collimator hole diameter on collimator sensitivity?

A

Decreases sensitivity

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39
Q

What is the typical spatial resolution in nuclear medicine images?

A

10 FWHM mm
(0.05lp/mm)

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40
Q

What controls contrast in NM imaging

A

Mainly controlled by relative uptake of the tracer in different tissues within the patient

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41
Q

Does scatter in NM improve or reduce contrast?

A

Scatter reduces contrast

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42
Q

How does PHA affect contrast/scatter when narrow/wide?

A

Narrower PHA rejects more scatter and improves contrast
Wider PHA accepts more scatter and recduces contrast

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43
Q

What is the typical PHA window width

A

Typically 15-20% of the photopeak

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44
Q

What is the effect of a lower resolution collimator on noise

A

Reduces noise
As allows more gamma rays to be detected

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44
Q

What is the effect of longer acquisition time on noise?

A

Reduces noise
As allows more gamma rays to be detected
But lower SR

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45
Q

What is the effect of increased injected activity on noise?

A

Reduces noise
As allows more gamma rays to be detected

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45
Q

What is the effect of shorter acquisition times on noise?

A

Increases noise
Less time for gamma rays to be detected - less gamma rays detected

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46
Q

What is the effect of a higher resolution collimator on noise

A

Increases noise
Less gamma rays detected
But higher SR

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47
Q

What is the effect of decreased injected activity on noise?

A

More noise as less gamma rays detected

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48
Q

How does Gallium-67 decay?

A

electron capture
It has too few neutrons

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49
Q

How does Technetium 99m decay?

A

Via gamma emission

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50
Q

How does Iodine-131 decay

A

via beta emission

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51
Q

How does Fluorine-18 decay

A

By positron emittion

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52
Q

How does Mo99 decay to 99mTc

A

By beta emission

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53
Q

What type of atom is emitted during alpha decay

A

Helium atom

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54
Q

What happens to the atomic number in alpha decay

A

Decreases by 2

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55
Q

What happens to the mass number in alpha decay

A

Decreases by 4

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56
Q

How long is a technetium generator useful for?

A

5 days

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57
Q

What does 99TC decay to?

A

99Ru

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58
Q

Why is Iodine 131 unstable and therefore how does it decay?

A

Has too m any neutrons
Decays via beta emission

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59
Q

Why is Fluorine-18 unstable and how does it therefore decay?

A

Has too many protons (too few neutrons)
Do decays via positron emission

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60
Q

Why is Mo99 unstable and therefore how does it decay?

A

It has too many neutrons
Decays via beta emission

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61
Q

What is the effect of higher energy gamma ray emission on patient dose?

A

Decreases patient does as less interaction/absorption in patient tissues

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62
Q

What is the effect of a short effective half life on patient dose?

A

When Teff is short, activity rapidly disappears from the body and the effective dose is lower

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63
Q

Does the radiosensitive weighting of tissues targeted by the radionuclide in NM affect patient dose?

A

Yes
Tissues targeted that have a higher tissue weighting factor will experiences an increased effective dose

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64
Q

Does an increase administered activity increase or decrease dose?

A

Increases dose

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65
Q

What is the effect of a high cut of frequency filter in filtered back projection?

A

Sharper features (better SR)
Higher noise

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66
Q

What is the effect of a low cut of frequency filter in filtered back projection on SR and noise?

A

Smoother features (worse SR)
Lower noise

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67
Q

What does OSEM stand for? What is it?

A

Ordered subset expectation maximisation
The most common reconstruction algorithm for PET images

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68
Q

Does the collimator in nuclear imaging reject scatter

A

NO

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69
Q

What is the role of dynodes in a PMT?

A

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

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70
Q

How do PET isotopes decay?

A

Via positron emission

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71
Q

What is the effect of a smaller FWHM (full width half maximum) on SR

A

Improves SR

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72
Q

What is the effect of a larger FWHM (full width half maximum) on SR?

A

Reduces SR

73
Q

What is the effect of a high resolution collimator in SPECT on SR?

A

Improves SR

74
Q

What is the effect of a low resolution collimator in SPECT on SR?

A

Reduces SR

75
Q

What is the effect of acquiring a larger number of projections in SPECT on SR?

A

Improves SR

76
Q

What is the effect of acquiring a lower number of projections in SPECT on SR?

A

Reduces SR

77
Q

What is the typical spatial resolution in SPECT (in FWHM)

A

10-15mm FWHM

78
Q

What is the effect of iterative reconstruction on attenuation and scatter in SPECT?

A

Provides attenuation correction and attenuation correct
Improving contrast

79
Q

What types of artefact can camera non uniformity cause in SPECT?

A

Ring artefacts

80
Q

How is attenuation variation typically corrected for in SPECT?

A

By using a low dose CT

81
Q

Name some examples of positron nuclides used in PET scanning

A

F18
C11
N13

82
Q

In PET what is the line between the detectors called?

A

Line of response

83
Q

In PET what is a true coincidence

A

When both 511keV gamma rays from a single annihilation event interact with a pair of detectors without prior scattering in the patient

83
Q

In PET:
What happens to the number of random events compared to true events when activity administered to patient increases

A

The number of random events increases much faster than the number of true events

84
Q

In PET:
What is a random coincidence?

A

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
Q

In PET:
What is a scatter coincidence?

A

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
Q

Is NaI crystal used in PET scanners

87
Q

Why are BGO or LSO crystals used in PET scanning rather than NaI (like is used in planar)

A

Because BGO and LSO are better than NaI for detection of 511keV gamma rays

88
Q

What is the SR of PET scans at the centre?

89
Q

What is the SR of PET scants at the periphery

90
Q

What 3 factors affect SR in PET?

A

Distance travelled by positron before annihilation
Non-colinearity
Size of individual detectors

91
Q

What is non-colinearity in PET?
What effect does this have?

A

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
Q

Is the SR of a PET scanner better at the centre of periphery of the detector?

A

SR of a PET scanner is best at the centre of the image and degrades towards the periphery

93
Q

Why types of scintillators are used for TOF PET

A

LSO or LYSO

94
Q

What is the purpose of time of flight PET

A

used to improve the accuracy of the reconstruction
As measures the time difference between the arrival of the gammas

95
Q

Does TOF PET improve or reduce SR

A

Improves SR

96
Q

Is the demand for FDG greater in normal tissue or tumour tissue

A

Tumour tissue

97
Q

What is the adult dose of 18FDG (in MBq/kg)

98
Q

What is the effective dose from 18FDG administration

99
Q

What are the typical administered activities in 18FDG studies (MBq) for an adult?

A

200-350 MBq

100
Q

What is the typical study time for FDG18 scans

A

20 minutes

101
Q

What causes a cold artifact in PET scanning

A

Created due to different patterns of breathing between the (much shorted) CT scan and the longer PET scan

102
Q

What can help reduce the effect of cold artefact

A

Asking the patient to use shallow breathing

103
Q

What does SUV stand for

A

Standard Uptake Value

104
Q

What is SUV the ratio of

A

FDG concentration in tissue: to injected activity per kg of the patient

105
Q

What can SUV be used to differentiate between

A

Benign and malignant lesions
And assess treatment response

106
Q

What is the rough cut off in SUV between malignant and benign lesions

107
Q

What factors can affect SUV (5)

A

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
Q

Is the SR in PET or SPECT better

109
Q

In PET:
What is the effect of longer acquisition times per bed position on image noise

A

Longer times reduce noise

110
Q

A MAG3 scan is dynamic or static?

111
Q

T/F - A DTPA scan is safe in patients with renal failure?

A

False. DTPA is cleared via glomeruli.

112
Q

DMSA scan is static or dynamic?

113
Q

Kidney Imaging - what are DMSA, DTPA and MAg3 used for?

A

DMSA - Kidney cortex
DTPA - eGFR
MAG3 - renal plasma flow

114
Q

What is SPECT?

A

3D version of planar, takes 30mins and uses multiple cameras and the images taken are overlaid.

115
Q

What is the effect of a high resolution collimator on SPECT image quality?

A

Improved SR

116
Q

What is the effect of acquiring a larger number of projections on SR in SPECT?

A

Improved SR

117
Q

What is the effect of using a high cut off filter during reconstruction on SR in SPECT?

A

Improved SR

118
Q

Why are SPECT images noisy? (3)

A

High resolution collimators
Limited time per projection
Mean low number of detected gamma rays

119
Q

What type of artefacts does camera non-uniformity cause in SPECT?

A

Ring artefacts

120
Q

How is CT used in SPECT imaging?

A

To correct SPECT images for attenuation (Attenuation correction)
Provided using low dose CT scan

121
Q

In PET imaging:
What happens to the number of random events (compared to the number of true events) as the activity administered increased?

A

The number of random events increases much faster to the number of true events

122
Q

In gamma imaging does the collimator reject scatter?

123
Q

In gamma imaging:
What is the role of the pulse height analyser window on image contrast?

A

Attempts to reject scatter
To improve image contrast

124
Q

In NM imaging how does a lower resolution collimator affect noise?

A

Reduced noise as more gamma rays accepted
However this reduces SR

125
Q

In NM how does longer acquisition time affect random noise?

A

Reduces noise
(however more change of motion artefact)

126
Q

In NM how does increased injected activity affect random noise?

A

Reduced noise
(however higher patient dose)

127
Q

In NM:
How does administered activity affect patient dose?

A

More injected activity
Higher patient dose

128
Q

In NM:
How does the energy of emitted gamma rays affect patient dose?

A

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
Q

In NM:
How does the bio-distribution of the pharmaceutical affect patient dose?

A

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
Q

In NM:
How does the effective half life of radionuclide affect patient dose?

A

When half life is short - rapidly disappears from the body and the effective dose will be lower

131
Q

What is the effective dose from FDG18 administration

132
Q

What is the effective dose from initial (low dose) CT in 18FDG scans

133
Q

Is a collimator required for PET scanning?

A

No
Relies on coincidence detection

134
Q

What is the spatial resolution in PET imaging?

A

FWHM of 4-5mm
(0.2 lp/mm)

135
Q

What does spatial resolution depend on in PET scanning (3)

A

Coincidence detection
Size of detectors and radius of detector ring
Choice of filter during reconstruction

136
Q

Are NaI detectors used in PET scanning?

137
Q

How is fluorine 18 (FDG) used in PET scanning produced?

A

In a cyclotron
by bombarding 18-Oxygen with protons

138
Q

How does a cyclotron produce raidonuclides?

A

By bombarding stable nuclei with highly energetic charged particles (typically protons)
Forcing neutrons out of the nucleus

139
Q

What are the two methods by which nuclear reactors create radionuclides?

A

Extraction of fission products
Production by neutron activation

140
Q

What is the disadvantage of nuclear reactors?

A

Relatively low yield of the desired radioisotope and the substantial production of other radioisotopes

141
Q

What are common radioisotopes produced in a nuclear reactor?

A

Mo 99 (by neutron bombardment)
131 I (by fission)

142
Q

What is the septal thickness, max keV, and radionuclide used for low energy collimators?

A

Thickness = 0.3mm
Max keV = 150
Radionuclide = 99mTc

143
Q

What is the septal thickness, max keV, and radionuclide used for medium energy collimators?

A

Thickness =1mm
Max keV = 300
Radionuclide Indium -111

144
Q

What is the septal thickness, max keV, and radionuclide used for high energy collimators?

A

Thickness =2mm
Max keV = 400
Radionuclide - Iodine 131

145
Q

How thick are the scintillation crystals in gamma cameras?

A

About 10mm

146
Q

Name 3 examples of static planar imaging

A

DMSA renal scan
Bone scan
Lung perfusion scan

147
Q

Name 3 examples od dynamic planar imaging

A

MAG3 renal scan
Gallbladder emptying scan
Gastric emptying scan

148
Q

When is gated imaging used in planar imaging?

A

When study organs have regular physiological motion
e.g cardiac imaging

149
Q

What is the typical matrix size for static imaging

150
Q

What is the typical matrix size for dynamic imaging?

A

128x128
or
256x256

151
Q

What is the typical matrix size for gated cardiac imaging

152
Q

What material are collimators typically made of

153
Q

Why are collimators typically made of lead

A

Due to high linear attenuation co-efficient

154
Q

Which has a thicker septa? Collimator used for 99Tcm imaging or collimator used for 131 Iodine imaging?

A

131 Iodine (keV = 364)

Note keV for 99Tcm = 140

155
Q

What happens if the septa in the collimator is too thin for the radionuclide used?

A

Increased probability of penetration by gamma photons that are not travelling parallel to the axes of the hole
Called septal penetration

156
Q

What is the result of septal penetration on image quality

A

Reduced image quality

157
Q

How many photomultiplier tubes are in a typical gamma camera

159
Q

What percentage of TC99m decays via internal conversion?

A

10%
90% is via isomeric transition

160
Q

What is electron capture?

A

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
Q

What is the decay constant?

A

The fraction of all the radioactive atoms in a sample that are disintegrating each second
Substance dependent

162
Q

How do you extract TC99m from a molybdenum technetium generator?

A

Pass saline through the molybdenum source

163
Q

What is the optimum time interval of extracting technetium from the generator?

164
Q

What is the PHA for Technetium 99m?

A

Window is 126-154 keV

165
Q

In nuclear medicine does the Collimator reject scatter?

A

No it has no role in scatter rejection in nuclear medicine

166
Q

How to increase spatial resolution in nuclear medicine studies? (3)

A
  1. Decrease patient to camera distance
  2. Increase collimator resolution
  3. Decrease patient motion
167
Q

Typical spatial resolution in nuclear medicine studies?

A

0.05 line pairs per mm

168
Q

How to increase contrast in Nuclear medicine studies?

A

Narrower Pulse height analyser window to reject more scatter

169
Q

How to reduce noise in nuclear medicine studies? (3)

A
  1. Use a lower resolution collimator
  2. Longer acquisition times
  3. Increase injected activity
170
Q

What 2 general factors affect patient dose from a radionuclide?

A
  1. Increase number of disintegrations in patient
  2. Energy deposition per disintegration
171
Q

How is spatial resolution in SPECT affected by resolution of collimator?

A

High resolution collimator gives high spatial resolution

172
Q

How to reduce Noise in Spect? (3)

A
  1. Inject more activity of radionuclide
  2. Choice of reconstruction filter
  3. Use resolution recovery reconstruction
173
Q

How to reduce noise in PET? (2)

A
  • 3D acquisition
  • longer acquisition time per bed position
174
Q

Alpha radiation vs Beta emission
Which is more strongly ionising?
Which is more penetrating?

A

Alpha is more strongly ionising
Beta is more penetrating

175
Q

The main artefact with back projection is …? Which occurs around which areas?

A

Star/streak artefact
Hot areas

176
Q

Isotopes share chemical properties or physical properties?

A

Only share chemical properties

177
Q

Tc99 decays by…?

A

Beta emission

178
Q

SPECT: How is spatial resolution affected by large number of projections?

A

Improves resolution

179
Q

SPECT: How is spatial resolution affected by a high cut-off filter during reconstruction?

A

Improves resolution

180
Q

SPECT: How is spatial resolution affected by circular orbits?

A

Reduced resolution
Non-circular is better for resolution

181
Q

True or false: Radionuclides decay exponentially

FRCR Part 1 Physics (20 decks)

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