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Huda > Chapter 14 Nuclear Medicine II > Flashcards

Chapter 14 Nuclear Medicine II Flashcards

1
Q

what is SPECT

A

single photon emission computed tomography
-tomographic views of distribution of isotopes

SPECT is to gamma camera imaging as chest CT is to chest radiographs

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2
Q

describe how SPECT acquires tomographic images

A

uses gamma cameras to get projection images, which are then processed to generate tomo images
gamma camera heads rotate around a central axis of rotation

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3
Q

what is distance from camera face to central axis

A

radius of rotation

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4
Q

what type of collimator is typically used for SPECT imaging?

A

parrallel hole collimators

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5
Q

what are fan-beam collimators

A

hybrid of parralel hole (y) and converging (x) holes
-better resolution in x-direction
-limited FOV
-used for brain SPECT

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6
Q

how many planar images does the scintillation camera acquire?

A

rotates 360 degrees around patient and takes 60 or 120 images obtained at 6 or 3 degree intervals
-scanning time ~ 20 MIN

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7
Q

Where are 180 degree rotations of the scintillation camera common?

A

cardiac imaging
64^2 matrix size

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8
Q

what did SPECT reconstruction originally use and why was it discontinued?

A

filtered back projection
-low number of counts yielded noisy and streaky tomo images

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9
Q

what is used for SPECT reconstruction now and why is it better than old method?

A

iterative reconstruction
more accurate and minimize artifacts

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10
Q

common iterative reconstruction method in SPECT

A

ordered subset expectation maximization

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11
Q

what type of volume data does SPECT generate?

A

isotropic
allows transverse, saggittal, and coronal views to be generated

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12
Q

what is frequency filtering in SPECT

A

-improves quality of SPECT images
-low-pass filter remove high frequencies, yielding smoother but less distinct edges for images
-high-pass filters pass higher frequencies, yielding noisier but sharper images with enhanced edge definition

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13
Q

why does SPECT use 2 or 3 gamma cameras

A

to reduce time required to acquire projection images

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14
Q

why are elliptical orbits used in SPECT

A

allows distance to the patient to be minimized

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15
Q

activity used for bone scans

A

800 MBq 99mTc
120 projections
128^2 acqisition matrix

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16
Q

activity used for cardiac SPECT

A

800 MBq 99mTc
180 degree rotation
60 projections
64^2 acquisition matrix

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17
Q

activity used for neuroendocrine or neurologic tumour

A

400 MBq 123I
360 degree rotation
60 projections
64^2 acquisition matrix

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18
Q

activity used for white cell scan

A

20 MBq 111In
360 degree rotation
60 projections
64^2 acquisition matrix

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19
Q

how often is the photopeak window of the pulse height analysis evaluated?

A

daily using a source that radiates the whole crystal

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20
Q

how are intrinsic floods performed

A

without collimator
point source 99mTc
assess performance of NaI and associated light detectors

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21
Q

how are extrinsic floods (uniformity) performedz?

A

check daily
place large disk of 57Co in front of camera

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22
Q

unacceptable non-uniformities

A

5%
-typically are 2-3%

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23
Q

how is linearity in SPECT checked?

A

-quadrant bar phantoms
-weekly

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24
Q

explain high-count uniformity acquisitions

A

-performed monthly for each camera head and collimator
-200 million for 128^2 matrix
-high count floods are used to obtain uniformity correction factors

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25
Q

how is center of rotation QA done

A

use pt source or line source
monthly

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26
Q

how is head tilt angle QA done

A

bubble level
quaterly

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27
Q

how is spatial resolution in air assessed

A

pt or line source
during acceptance testing

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28
Q

what is Jaszczak phantom used for?

A

assess spatial resolution, unfiformity, and image contrast
quaterly

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29
Q

is spatial resolution for SPECT worse than planar imaging?

A

yes, it is poorer because SPECT images are derived from planar images

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30
Q

major benefit of SPECT over planar images

A

improved contrast from the elimination of overlapping structures

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31
Q

what does SPECT image reconstruction amplify?

A

-image noise
-non-uniformities

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32
Q

how do non-uniformities appear in SPECT images?

A

as ring artifacts

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33
Q

how are partial ring artifacts produced

A

from multi-head SPECT systems when projections are not acquired by all heads over a 360 degree arc

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34
Q

scintillators used for PET

A

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

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35
Q

important PET scintillator properties

A

photoelectric absorption efficiency
energy resoltuion
light decay time

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36
Q

compare the different PET scintillator properties

A

BGO has best absorption but worse energy resolution\
GSO and LSO emit more light- better energy resolution
GSO and LSO: shorter decay time- better performed at high count rate

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37
Q

how are PET crystals arranged?

A

6x6 or 8x8 blocks
36-64 crystals per detector block
each block is coupled to array of PMT, which provide positional info and offer PHA capability

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38
Q

how are detector blocks arranged?

A

in a ring
several rings are arranged concentrically

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39
Q

how many crystals and blocks in current PET systems

A

up to 20000 crystals in 400 blocks

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40
Q

what energy range is used to identify annihilation photons in PET

A

450-550 keV

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41
Q

true coincidence event

A

two interactions have to occur within a time interval tau

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42
Q

what % of detected photons are accepted by coincidence circuitry?

A

1%

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43
Q

what is line of response

A

simultaenous detection of 2 events

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44
Q

what is the line of response data used to create?

A

sinogram
projection vs angle

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45
Q

what is used to reconstruct images in PET?

A

iterative reconstruction

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46
Q

time of flight PET

A

uses difference in arrival times of the 2 annihilation photons
-improves spatial res

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47
Q

what coincidences are there in PET?

A

true
scatter
random

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48
Q

2D mode vs 3D mode PET

A

2D mode: septa are present to define planes. Coincidences are not detected between adjacent rings.
3D mode: septa are removed. More sensitive but more scatter and random events. Coincidences are detected between adjacent rings

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49
Q

are septal collimators needed for localization of photons in PET

A

No

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50
Q

what is FORE in PET

A

fourier rebinning
used to rebin 3D data into 2D data sets

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51
Q

3D vs 2D PET scanner sensitivity

A

3D is 6 X higher than 2D

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52
Q

most common PET radionuclide

A

18F

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53
Q

how is image plane uniformity in PET QAd

A

-cylinder filled with positron emitter
-every 2 weeks

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54
Q

how is detector calibration done in PET

A

-positron source in FOV
-frequency is recommended by vendor

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55
Q

how are PET sensitivity counts measured?

A

counts/MBq
sleeved rod source
annually

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56
Q

how is spatial resolution of PET assessed?

A

inspect sinogram and image of a point source
check annually

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57
Q

how are count rate performance and scatter fraction of PET assessed?

A

-line source in polyethylene cylinder
-annually

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58
Q

how is PET system performance evaluated?

A

-includes uniformity ad hot sphere contrast
-standard ACR phantom
-every 6 months

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59
Q

compare PET images to planar gamma camera images

A

-PET more sensitive, high counts, lower mottle
-PET uses several million counts, 10X more than planar images

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60
Q

how is ultimate limit of spatial resolution determined?

A

range of positron
82Rb has worse res than 18F because of longer distance travelled by 82Rb positrons

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61
Q

spatial resolution of PET detectors

A

5 mm FWHM
PET resolution is worse at edge than center because 511 kEv photons may be detected by adjacent detectors

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62
Q

where do partial volume artifacts occur in PET?

A

for lesions < 2 X FWHM (i.e. 10 mm lesions)
-activity of small lesions is blurred by imaging system (FWHM)

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63
Q

what do faulty detectors cause in PET?

A

angled black line in sinogram
faulty block yields thicker angled black strip in sinogram

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64
Q

why do we co-register nuc med images with CT?

A

improve lesion localization
attenuation correction

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65
Q

how many slices in CT scanner for PET/CT

A

16 for most
64 for cardiac

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66
Q

how long does it take to do spiral CT scan from eyes to upper thigh?

A

20 s

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67
Q

CT image acquisition parameters

A

120 kV
512^2 matrix size
5 mm slice thickness
pitch of 1.5

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68
Q

SPECT and PET acquisition time vs CT acquisition time

A

20-30 minutes vs 20 s

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69
Q

CTDI for PET/CT CT scan

A

2 mGy (L) for low dose for attenuation correction and fusion only
15 mGy for disgnostic quality image

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70
Q

why does SPECT show lower activity at patient center vs periphery?

A

attenuation
CT image is used to correct the attenuation factor and show the true activity distribution

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71
Q

what cm of tissue attenuates half the activity of 99mTc

A

5 cm attenuates half
10 cm reduces activity to 1/4

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72
Q

most common use of SPECT/CT

A

myocardial perfusion imaging

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73
Q

where does misregistration artifact come from

A

SPECT and CT are not acquired simultaneously- any organ motion can yield misregistration artifacts

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74
Q

what body parts are most concerning for creating apparent defects in SPECT due to attenuation

A

diaphram
breast

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75
Q

in PET and SPECT, how to correspoind attenuation factors with CT image

A

since CT energy is lower, have to extrapolate attenuation coefficients for PET/SPECT based on known attenuation properties of tissues
-issues with metallic implants

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76
Q

what does attenuation in PET depend on?

A

TOTAL thickness of tissue

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77
Q

for a large person, what is % loss of counts due to attenuation in PET?

A

95%

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78
Q

what can cause hot artifacts in CT attenuation corrected PET images?

A

contrast material
implanted metal objects
increased acitivity near venous structures if intrevaneous contrast is used

hot spots adjacent to strong attenuators should always be confirmed on non-attenuation corrected images

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79
Q

what activity is administered for PET

A

600 MBq of 18F 90 min prior to iaging

80
Q

axial coverage in PET for single detector position

A

20 cm

81
Q

time for PET scan at each detector position

A

2-3 min
current PET scans use 5 detector positions to cover body

82
Q

what organs receive the highest doses

A

those that take up activity
reduced organ size = higher dose
dose is high for thyroid, spleen, gallbladder, liver

83
Q

highest organ doses from diagnostic nuc med

A

10-50 mGy

84
Q

average effective dose for 99mTc

A

4 mSv
1.5 mSv for lung scans to 9 mSv for stress cardiac studies

85
Q

effective doses for PET scan using 800 MBq 18F

A

8 mSv

if CT portion is diagnostic- get additional 15 mSv
if CT is for anatomy and attenuation correction, get additional 2 mSv

86
Q

what is nice about beta minus emitters?

A

beta particle energy is primarily deposited in the organ taking up the radionuclide

87
Q

what is 131I administered for?

A

hypothyroidism
thyroid cancer

thyroid dose to a patient receiving 370 MBq od 131I with 50% thyroid uptake is 200 Gy

88
Q

radionuclides used for therapy

A

phosphorus-32 -polycythemia vera
strontium-89 - osseous mets
yitrium-90 - liver neoplasms
iodine-131 - thyroid

89
Q

doses from patients after injection of radipharmaceuticals at 1 m

A

10 uSv/h for most
100 uSv/h for 18F
50 and 300 uSv/h for 131I hyperthyroidism and cancer

90
Q

when is NRC notified- unintended radiation exceeds what level?

A

50 mSv effective dose
500 mGy organ dose

91
Q

when can 131I patients be released?

A

activity < 1.2 GBq

92
Q

breastfeeding cessation?

A

-not needed for 18F
-24 h for 99mTc
several months for 131I
a week got 67Ga or 111I

93
Q

where should volatile radionuclides be stored?

A

fume hoods

94
Q

dose rate to hands from radiopharmaceutical (lead) syringes

A

0.2 mGy/h/MBq

95
Q

syringe shields

A

reduce extremity doses threefold

96
Q

how are extremity doses monitored?

A

ring dosimeter

97
Q

what do nuc med operators who risk intake of radionuclides undergo for safety?

A

bioassay (thyroid monitoring for iodine uptake)

98
Q

what is major source of staff exposure in nuc med?

A

patients who were administered several hundred MBq of 99mTc

99
Q

are lead aprons effective in nuc med?

A

less so than in imaging because of higher gamma ray photon energies

100
Q

nuc med tech’s effective dose

A

2-4 mSv/year

101
Q

what is done to packages with radioactive labels?

A

monitored for surface contamination

102
Q

nuc med safety items

A

wipe tests
daily surveys in areas where written directive procedures are carried out

103
Q

what to do in event of minor spill

A

containment
decontamination
notify RSO

104
Q

what to do in event of major spill

A

reqire presence of RSO

105
Q

what activity constitutes a major spill

A

> 4 GBq of 99mTc
40 MBq of 131 I

In Canada it’s 100 times exemption

106
Q

how long before radioactive waste can be disposed of with normal waste?

A

10 half lives

107
Q

is excreta in sewer system regulated?

A

no, people can poop as they need to

108
Q

bone spect most likely uses what kind of collimator and what energy?

A

low energy and high resolution parralel hole collimators

109
Q

are collimators used in PET?

A

No
spatial info is not obtained from parrallel-hole collimators as in planar imaging, bt by detection of annihilation radiation in coincidence

110
Q

how is spatial info in PET obtained?

A

use PHA to identify 511 keV photons
in coincidence to generate lines of response

111
Q

when are personel provided with a dosimeter?

A

occupational dose limit exceeds 10% of a dose limit

In Canada when you approach 5 mSV per year or 50 mSV per year to hands or feet

112
Q

number of projection images in SPECT study

A

60

113
Q

what radionuclide is used to get extrinsic gamma camera floods?

A

57Co

114
Q

what does SPECT image reconstruction do to non-uniformities

A

amplifies them

115
Q

is spatial resolution of 82Rb better or worse than 18F?

A

worse because 82Rb travels further

116
Q

CTDI for scan for attenuation correction only

A

2 mGy
less than diagnostic CT scan

117
Q

average patient effective dose for 99mTc

A

4 mSv

118
Q

what would ideal radionuclide emit?

A

purely beta minus
-electrons would deposit all their energy in the uptake region

119
Q

spatial resolution of gamma camera

A

2-3 mm FWHM intrinsic
8-10 mm FWHM with collimator
CT is 100 um in comparison

120
Q

components of gamma camera

A

-multihole or pinhole collimator
-NaI scintillator- turns energy from gamma ray into many light photons
-light pipe: directs scintillation photons onto phototube
-PMT: convert energy from scintillator photons into electronic signal
-energy circuit: measures energy of detected photon

121
Q

arrangement of PMTs in gamma camera

A

close-packed hexagonal

122
Q

where does gamma camera position a gamma that underwent compton and PE effect

A

-camera will think the PE effect occured at a lower energy-some of the energy was lost to compton

123
Q

gamma camera scintillator efficiency wrt energy

A

as gamma energy increases, efficiency goes down, because PE is proportional to 1/E^3

124
Q

gamma camera- what % of scintillation photons reach PMT array?

A

30%

125
Q

light photon to photoelectron conversion efficiency in NaI

A

~ 25%

126
Q

how does gamma camera relative energy resolution and intrinsic spatial resolution vary with E?

A

1/root(E)

127
Q

energy windows for gamma camera

A

-lower energy counts are from Compton
-min energy is from backscatter out of detector or in patient
-max scatter energy is from backscatter in detector
-multiple scattered photons have very low E

128
Q

light pipe

A

-couples PMT to NaI crystal
-thicker light pipe improves linearity but reduces intrinsic spatial resolution

129
Q

pincushion distortion

A

increased count density in center of PMT tubes

130
Q

spatial non-linearity in gamma cameras

A

-non-random mis-positioning of events
-results from positioning circuits shifting location of an event towards closest PMT
-look-up tables correct for this mis-positioning

-also cause spatial non-uniformities

131
Q

how to correct for spatial non-uniformities

A

-acquire image of uniform sheet source and generate correction map

132
Q

gamma camera collimator material

A

high Z
high density

133
Q

collimator geometric efficiency

A

-for parrallel holes
-fraction of gamma rays passing through the collimator per gamma ray emitted by source
–g is independent of distance from source to collimator (b) exceot for single-hole (1/b^2)

134
Q

collimator spatial resolution

A

resolution worsens as source moves away fro collimator face

135
Q

system spatial resolution

A

square root of (intrinsic res ^2 + collimator res^2)

-collimator is what limits the system spatial resolution

136
Q

how to improve intrinsic spatial resolution

A

-smaller PM tube
-thinner light pipe
-use pre-amplifiers to limit PM tube position summation to only tubes near the interaction event

137
Q

gamma camera dynamic non-uniformities

A

-due to different orientations of gamma camera wrt earth’s magnetic field, or temperature changes throughout day
-minimize by magnetically shielding each phototube and through use of on-the-fly tuning

138
Q

expected uniformity for gamma camera

A

integral (over whole system) with 3.5% and differential (over ROI) within 2 %

139
Q

gamma camera count rate performance

A

front end of gamma camera is paralyzable
back end is not paralyzable

140
Q

high count rate mode for gamma camera

A

-adaptive rezoning
-decrease PMT integration time (directly increases error in energy resolution of each event)
-used for 3D cardic imaging, high resolution brain imaging, and PET imaging)

141
Q

what is adaptive rezoning for gamma camera

A

-only subset of PMTs closr to location are used to process event
-other zones respond in parrallel fashion
-degrades system energy resolution because less light photons are collected on a per event basis
-degrades spatial resolution since PMTs in one active session are still exposed to light photons from another active session

142
Q

NEMA

A

National Electrical Manufacturer’s association

143
Q

intrinsic energy resolution of gamma camera

A

FWHM = 9% at 140 keV

144
Q

gamma camera intrinsic count rate performance

A

normal = 180 kcps
high mode = 268 kcps

145
Q

gamma camera system sensitivity

A

105 counts/s/MBq
high resolution is 73 counts/s/MBq

146
Q

semiconductor gamma cameras

A

-energy from interacting gamma ray is converted directly to electronic signal
-more efficient conversion
-better energy resolution

-cadmium zinc telluride (CZT) is semiconductor

147
Q

blur tomography

A

activity from defined plane is in focus while planes above or below are out of focus

148
Q

reconstruction algorithm for rotating gamma camera (SPECT)

A

filtered backprojection

149
Q

why does resolution depend on collimator to source distance?

A

the further away the collimator is, the more voxels the collimator holes will see

150
Q

SPECT center of rotation error

A

-misalignment of central image axis with axis of rotation
-causes blurring and donut artifact

151
Q

SPECT head tilt error

A

-blurring in coronal and sagittal views of pts far from axis of rotation

152
Q

SPECT collimator hole misalignment

A

-collimator holes not parrallel to each other and perpendicular to collimator face- can cause center-of-rotation and head tilt error

153
Q

SPECT non-uniformity leads to what artifact?

A

-bull’s eye and ring artifact
-for both static and dynamic non-uniformity

154
Q

SPECT motion artifacts appear as what?

A

blurring, streaks

155
Q

SPECT activity outside of FOV appears as what?

A

-streaks at edges of reconstructed FOV

156
Q

SPECT artifacts that cannot be avoided

A

-system spatial resolution (depends on source to collimator distance b)
-photon attenuation and scatter

157
Q

compensating for spatial resolution dependence in SPECT

A

-lesions deep in body not as well resolved as those on surface
-filter with resolution recovery filter
-keep camera head as close to patient as possible
-use converging collimator
-can improve overall spatial resolution but cannot correct for change in spatial resolution with depth

158
Q

in SPECT- how to compensate for scatter with windows?

A

-subtract image containing only scattered photons from one containing both scattered and unscattered photons
-use windows to estimate amount of scatter contaminating photopeaks image

159
Q

holospectral imaging

A

use several energy windows to create multiple images and use linear alegbra to create scatter-free projection image
-SPECT

160
Q

can SPECT projection equation with attenuation be inverted using standard filtered backprojection techniques?

A

no

161
Q

SPECT- scattered photons- effect on correcting attenuation

A

-amount of attenuation is less than would be anticipated because scattered photons are detected in place of some of the attenuated, unscattered photons

-2 techniques to account for attenuation- pre-processing and post-processing
-both assume u is constant within a defined boundary and there is no attenuation outside this boundary

162
Q

problems with SPECT attenuation correction techniques

A

-assume homogeneous tissue density
-patient contour must be precisely defined
-doesn’t account for collimator response function
-assumes u is independent of depth (u depends on scatter)

-CT SPECT measures u directly for each SPECT slice

163
Q

type of noise in SPECT planar images

A

white

164
Q

SPECT Hahn filter

A

dampens higher frequency, linear

165
Q

SPECT Butterworth filter

A

dampens higher frequency, looks cosine shaped

166
Q

MTF for perfect response

A

flat
1

167
Q

problems with SPECT filtered backprojetion

A

-accuracy is not good
-slow to acquire
-poor spatial resolution

-better results obtained with alternative inversion technique
-filtered backprojection oversimplies photon detection kernel so that it can invert it- better not to do this

168
Q

2 processes that photon detection kernel must model in SPECT

A

-photon propagation from pt of emission to face of collimator, including photon absorption and scatter inside phantom
-camera detection process including photon acceptance probability as function of incident angle and photon energy

169
Q

MLEM in SPECT

A

-maximum likelihood expectation maximization algorithm
-iterative technique

-good quality but slow
-error increases for large number of iterations
-based on Poisson noise
-preserves total image counts
-uses a priori info

170
Q

OSEM in SPECT

A

ordered subset expectation maximization

-modified from MLEM
-in MLEM, all projection data is used for each iteration
-OS-EM groups projection data into subsets and reconstructed voxel vlues are updated after each subset is evaluated
-faster than MLEM
-includes all advantages of MLEM
-mean square error also keeps decreasing for large number of iterations

171
Q

crystals in PET compared to SPECT

A

PET scintillator crystals are thicker (more efficient)

172
Q

gate window

A

when a 511 keV photon is detected, a timing gate is opened for a short time interval
-if 2nd photon is detected within this gate window, the 2 events are in coincidence

173
Q

LOR

A

line of response
-line between 2 detectors registering coincident events
-assume annihilation event occurred along LOR

174
Q

probability that 2 random events are detected as LOR in PET depends on what?

A

increases with count rate

175
Q

time of flight PET

A

can figure out timing distance between 1st and 2nd detection and pinpoint where annihilation occurred

176
Q

width of timing gate window

A

determined by gantry geometry
-longer than time required for photon to travel across ring of detectors (7-10 ns)

177
Q

types of events in PET

A

-true coincident event
-misplaced coincident event
(one or both photons created in a single annihilation event scatter before being detected)
-random event (2 detectors activated by photons from different annihilation events)

178
Q

formula for true coincident events

A

true = measured - scattered - random

179
Q

2D PET mode

A

only coincident events occuring in same (or possible adjacent) rings are recorded and reconstructed
-absorbing septa are used to prevent photons from other planes from being detected

180
Q

3D mode PET

A

absorbing septa are not used and coincident events from any two detectors are recorded and used in the reconstruction

181
Q

PET data for each patient

A

1 GB

182
Q

number of LORs in PET

A

n(n-1)
n is # of detectors in ring

183
Q

scintillation crystals for PET

A

-NaI
-CsF or BaF2- fast but expensive
-BGO- high efficiency for 511 keV photons
-LYSO, LSO, GSO- faster and more efficient than BGO, higher light output = better energy discrimination, faster light decay = higher counting rates

184
Q

2D PET reconstruction algorithms

A

-filtered backprojection
-os-em

185
Q

3D PET reconstruction algorithms

A

-cone beam and iterative techniques
-filtered backprojection or OSEM with and without attenuation and scatter corrections

186
Q

factors that affect spatial resolution in PET

A

-positron range
-non-colinearity
-detector size

187
Q

explain non-colinearity in PET

A

Ek of positron must be spent before combinging with electron
-due to Ek of positron and electron, annihilation photons are non-colinear
-variation in emission angle degrades resolution by ~ 2mm at center of whole body

188
Q

explain detector size effect on spatial resolution

A

-smaller detectors = better spatial resolution
-compton scatter from one detector to another becomes a problem for small NaI crystals and therefore crystals with higher Z can be used

189
Q

spatial resolution of current PET scanners

A

3 mm FWHM

190
Q

PET artifacts and sources of error

A

-scatter
-attenuation
-random coincident events
-noise
-deadtime

191
Q

scatter in PET

A

-detectors don’t have enough energy resolution to differentiate photons scattered in the patient from unscattered photons
-septa between rings can reduce out-of-plane scattering
-can use techniques to correct for in-plane scatter
-scattered events in PET can appear to come from lines outside the patient’s body (unlike in SPECT)

192
Q

is attenuation worse for PET or SPECT?

A

-less of a problem in PET than in SPECT because the 511 keV photons are less attenuated in the tissue than the SPECT photons, and also because 2 photons are detected in coincidence
-since 2phoons are along one LOR in PET, source along the line is equally attenuated independent of depth of annihilation in the patient

193
Q

how to measure attenuation factor in PET?

A

-do a transmission scan, prior to injecting the activity into the patient, using a rotating rod source

194
Q

how to measure random coincidences in PET

A

-use 2 coincidence windows of the same lenght
-true windown contains both true and randome events
-delayed window only gets random events
-subtract delayed from true

195
Q

advantages of PET

A

-better spatial resolution than SPECT (2-3 mm FWHM) but not as good as CT or MRI
-higher sensitivity than SPECT (no collimator) and ring geometry = faster image acquisition
-can correct for attenuation and scatter- images are a quantitative measure of radionuclide
-some radionuclides are biologically important, therefore organic material can be labelled if chemistry is fast enough

196
Q

advantages of PET

A

-better spatial resolution than SPECT (2-3 mm FWHM) but not as good as CT or MRI
-higher sensitivity than SPECT (no collimator) and ring geometry = faster image acquisition
-can correct for attenuation and scatter- images are a quantitative measure of radionuclide
-some radionuclides are biologically important, therefore organic material can be labelled if chemistry is fast enough

197
Q

disadvantages of PET

A

-requires accelerator to produce radionuclides (they are short lived)
-ring geometry PET scanners are same price as CT scanner
-expensive

Huda (20 decks)

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