Image Quality Flashcards
(10 cards)
What 3 factors introduce blur into PET images?
- detector geometry
- non-collinearity
- positron range
What are the 3 types of coincidence events in PET?
- True signal
- Random: minimize with timing window
- Scatter: minimize with energy threshold
Why is attenuation important in SPECT and PET?
- Cupping artifact: x- or gamma rays that traverse long paths produce fewer counts
- false hot areas at surface, false cool areas at depth (misdiagnosis)
What does detector geometry refer to?
Detector size, distance from isocenter, crystal size
What is non-collinearity?
opening angle is greater than 180 degrees (moving frame), detector separation
Collinearity: Annihilation photons are generated simultaneously
and back to back (nearly)
What is positron range?
distance travelled before annihilation
What causes a truncation artifact?
patient outside of CT FOV is not corrected for attenuation
What do random events depend on?
coincidence time window
single count rate for each detector pair (time delay)
What do scatter events depend on?
attenuation coefficient
object size
Activity / dose
time window
scintillator speed
