Chapter 4 Flashcards
What size of axial FOV do early PET or PET/CT scanners have?
12cm
15cm
18cm
20cm
15cm
What size of axial FOV do newer PET or PET/CT scanner systems have?
15-20cm
18-20cm
20-26cm
22-30cm
20-26cm
What 4 PET scanner system designs are there besides the full-ring system?
Partial Ring
Full Ring
Gamma Camera Coincidence Imaging
Panel RIng
What is the source material that is housed in the scanner for calibration of the detectors?
Ga-68
Cs-137
F-18
Ge-68
Ge-68
What should the depth of the crystal be to provide enough thickness to effectively stop the 511keV annihilation photons?
10mm
20mm
15mm
14mm
20mm
What detector module have manufactures migrated to create digital systems that have improved speed and short coincidence time resolution (250psec)?
SiPM
What is the line along which a the annihilation interaction occurs in the annihilation photon pair is detected by crystals on opposing sides?
line of response (LOR)
What is the lead or tungsten plates between each ring of individual crystals?
septa
Each ring of detectors have septa in place may only detect photons coming from with in the direct plane.
2D or 3D imaging?
2D
When septa are removed or moved out of the way, with no septa to restrict the angel of acceptance of annihilation photons.
2D or 3D imaging?
3D
3D imaging sensitivity is ______ times better than 2D imaging.
2 to 3
5 to 12
4 to 10
8 to 10
4 to 10
If there is a smaller angle of acceptance , is the sensitivity higher or lower at the center?
higher sensitivity
When the annihilation event interaction takes place, the 2 photons are not absorbed in the body, and they arrive directly into opposing detectors.
This is called what?
True event
Random event
Scatter event
True Event
When 2 photons from different decaying atoms arrive into opposing crystals with in the coincidence timing window and a false LOR is created.
This is called what?
True event
Scatter event
Random event
Random event
Detected when one or both of the photons undergo a scatter interaction, which also creates a false LOR.
This is called what?
True event
Scatter event
Random event
Scatter event
The overall effect of detecting false LORs is a substantial (increase or decrease) of the contrast in the image?
decrease
Corrections for both _______ and ______ events are absolutely required during the reconstruction process to produce a useful image.
random and scatter events
The fraction of detected events that are from scattered photons is called what?
Scatter fraction
What is the dominant type of interaction at 511keV?
True event
Scatter event
Compton scattering event
Random event
Compton scattering event
What are the ranges of energy windows for old and new scanners?
Old 350keV-650keV
New 425keV-600keV
What fraction is dependent on the amount of radioactivity both within the FOV and adjacent to the scanner, where single photons from out the FOV may be detected and contribute as a random event?
Scatter fraction or Randoms fraction
Randoms fraction
The noise equivalent count rate (NECR) may be used to measure _________.
signal-to-noise ratio
What is the equation for NECR?
T^2 / (T+S+R)
T= true count rate
S=scatter coincident count rate
R=randoms count rate
These following factors allow the use of what for PET imaging?
-Use of small crystals
-The creation of an LOR between 2 crystals to record the pathway of the radiation
-The use of coincidence-timing window to record and hopefully capture the data of true events
electronic collimation