PET/CT EXAM QUESTIONS AND
ANSWERS 100% CORRECT
Positron Emission Tomography (PET) - ANSWER-positron electron- positively charged
emission- radioactivity emitted from subject
tomography- tomo is latin for slice
Annihilation - ANSWER-two 511 KeV gamma rays emitted
Detector material- High light yields result in: - ANSWER-good energy resolution
Detector material- High atomic number/density results in: - ANSWER-efficient detection,
increases the stopping power
Detector material- Short decay time results in: - ANSWER-good timing rate and count
statistics
Available scintillation crystals (light yield): - ANSWER-NaI(Tl) (100)
LSO (75)
GSO (30)
BGO (15)
BGO is the most common crystal - ANSWER-It has the best intrinsic efficiency but has
a low light output. Has high stopping power of 511 keV gamma-rays
PET detector configuration made of cinfiguration of rectangular cube-shaped crystals -
ANSWER-4mm in size
10-30 mm in length
True events: - ANSWER-Two photons that strike the opposite crystals within the
coincidence timing window
Delay Event: - ANSWER-an event falling outside a timing window of > 12 nanoseconds
Coincidence Timing Window: - ANSWER-measures the arrival time interval of the
electrical pulses
Scatter Photons: - ANSWER-are normally reduced by selecting a relative narrow energy
window
Groups of crystal form a: - ANSWER-block
, Crystals are too small to have their own PMT's - ANSWER-Usually 4 PMT's are used on
a block
Several detector blocks are combined to form a: - ANSWER-"bucket" or modules
Modules are arranged in arrays to form: - ANSWER-full rings (there are between 18 to
32 rings)
More detector mean: - ANSWER-more sensitivity, use less activity, shorter scan time,
more $$
A typical scanner has ____________ crystals - ANSWER-8,000-20,000 crystals
The spatial resolution value of PET images is close to - ANSWER-the size of the crystal
(3-5mm)
PET vs. SPECT resolution - ANSWER-4mm for PET
>12mm in SPECT
Intrinsic resolution is related to: - ANSWER-detector crystal size
Spatial resolution is influenced by: - ANSWER--Face size of the detectors
-Detector thickness
-Detector separation
-Data smoothing during and after reconstruction
-It is most determined by :
The size of the crystal(detector) and their separation.
Coincidence timing window: - ANSWER-4.5-20 ns
The LOR's are - ANSWER-are stored during data acquisitions and the raw data must
first be reformated into sinograms. Each sinogram represents the one image slice.
Reconstruction - ANSWER--Process of converting counts along various LORs to
images
-Large scale algebra problem
-Each LOR between detector pairs provides an equation
Filtered Backprojection (FBP) - ANSWER--fast
-derived from CT reconstruction
-perfect with high counts, uniform sampling of LORs and no physical effects
-For PET: smooth, interpolate, and pre-correct
FBP creates... - ANSWER-severe streak or star artifacts, increasing image noise.
ANSWERS 100% CORRECT
Positron Emission Tomography (PET) - ANSWER-positron electron- positively charged
emission- radioactivity emitted from subject
tomography- tomo is latin for slice
Annihilation - ANSWER-two 511 KeV gamma rays emitted
Detector material- High light yields result in: - ANSWER-good energy resolution
Detector material- High atomic number/density results in: - ANSWER-efficient detection,
increases the stopping power
Detector material- Short decay time results in: - ANSWER-good timing rate and count
statistics
Available scintillation crystals (light yield): - ANSWER-NaI(Tl) (100)
LSO (75)
GSO (30)
BGO (15)
BGO is the most common crystal - ANSWER-It has the best intrinsic efficiency but has
a low light output. Has high stopping power of 511 keV gamma-rays
PET detector configuration made of cinfiguration of rectangular cube-shaped crystals -
ANSWER-4mm in size
10-30 mm in length
True events: - ANSWER-Two photons that strike the opposite crystals within the
coincidence timing window
Delay Event: - ANSWER-an event falling outside a timing window of > 12 nanoseconds
Coincidence Timing Window: - ANSWER-measures the arrival time interval of the
electrical pulses
Scatter Photons: - ANSWER-are normally reduced by selecting a relative narrow energy
window
Groups of crystal form a: - ANSWER-block
, Crystals are too small to have their own PMT's - ANSWER-Usually 4 PMT's are used on
a block
Several detector blocks are combined to form a: - ANSWER-"bucket" or modules
Modules are arranged in arrays to form: - ANSWER-full rings (there are between 18 to
32 rings)
More detector mean: - ANSWER-more sensitivity, use less activity, shorter scan time,
more $$
A typical scanner has ____________ crystals - ANSWER-8,000-20,000 crystals
The spatial resolution value of PET images is close to - ANSWER-the size of the crystal
(3-5mm)
PET vs. SPECT resolution - ANSWER-4mm for PET
>12mm in SPECT
Intrinsic resolution is related to: - ANSWER-detector crystal size
Spatial resolution is influenced by: - ANSWER--Face size of the detectors
-Detector thickness
-Detector separation
-Data smoothing during and after reconstruction
-It is most determined by :
The size of the crystal(detector) and their separation.
Coincidence timing window: - ANSWER-4.5-20 ns
The LOR's are - ANSWER-are stored during data acquisitions and the raw data must
first be reformated into sinograms. Each sinogram represents the one image slice.
Reconstruction - ANSWER--Process of converting counts along various LORs to
images
-Large scale algebra problem
-Each LOR between detector pairs provides an equation
Filtered Backprojection (FBP) - ANSWER--fast
-derived from CT reconstruction
-perfect with high counts, uniform sampling of LORs and no physical effects
-For PET: smooth, interpolate, and pre-correct
FBP creates... - ANSWER-severe streak or star artifacts, increasing image noise.
