Part 13: Gamma Camera Imaging
1.
Mark true or false before each of the statements below regarding gamma camera
imaging.
___
a) Spatial resolution is better in a 9.4 mm thick NaI(Tl) crystal than for a
6.4 mm crystal.
___
b) Energy resolution is better for imaging I-131 than for Tc-99m.
___
c) The intrinsic efficiency for counting I-131 photons is greater than for
Tc-99m photons.
___
d) Spatial resolution is better in imaging Tc-99m than for Tl-201.
___
e) The Compton scatter component in images of Tc-99m is greater that in Tl-201
images.
___
f) Spatial resolution is better in gamma cameras with 75 PMT’s than with 37.
2.
The intrinsic spatial resolution of current generation Anger cameras is _____
mm FWHM.
a)
1-2
b)
2-3
c)
3-4
d)
4-5
e)
10-12
3. Mark True or false before each of the
statements below regarding dead time in gamma camera imaging:
___ a) The gamma camera system is non-paralyzable.
___ b) The dead time of current generation gamma cameras is on the
order of 0.3 microsecond.
___ c) Imaging protocols should exceed 100,000 counts per second in
order to prevent significant count rate losses due to dead time.
___ d) A gamma camera with 75 PMT’s exhibits greater dead time than
for 37 PMT’s.
___ e) Intrinsic image resolution is best when the gamma camera
operates near its maximum possible count rate.
4.
Mark True or false before each of the statements below regarding gamma camera
collimators:
___ a) Compared to high energy collimators, low energy collimators
have thin lead septa.
___ b) Long bore collimators exhibit better spatial resolution than
short bore collimators.
___ c) High energy collimators have better spatial resolution than low
energy collimators.
___ d) High energy collimators have greater sensitivity than low
energy collimators.
___ e) Diverging collimators for imaging small sources have greater
sensitivity than parallel hole collimators.
___ f) The sensitivity of parallel hole collimators decreases
slightly as the distance between the source and collimator increases.
5. The system spatial resolution of current generation gamma
cameras fitted with a high-resolution low-energy collimator for imaging of
Tc-99m at a distance of 10 cm is approximately ____ mm FWHM.
a)
4
b)
7
c)
10
d)
12
e)
16
6. Mark true or false for each statement below regarding field
uniformity characteristics of gamma cameras.
___ a) PMT tube balance is the most important factor in
maintaining good field uniformity.
___ b) Setting a photopeak energy window asymmetrically high
results in flood images that show the PMT pattern as cold spots.
___ c) Count differences of at least 6% must exist for
non-uniformities in a routine flood image to be seen by visual inspection.
___ d) Field uniformity improves as the count rate increases.
___ e) Field uniformity is independent of photon energy.
7. Specifications for gamma camera performance are reported for
its useful-field-of-view (UFOV) and central field-of-view (CFOV), which are
defined to be ___ of collimated
field-of-view, respectively.
a)
95% and 75%
b)
100% and 75%
c)
90% and 50%
d)
75% and 50%
e)
100% and 80%
8.
Mark true or false before each statement below regarding gamma camera imaging
and Compton scattered radiation.
___ a) Acceptance of small-angle scattered radiation reduces
image contrast.
___ b) Rejection of scatter is most problematic for high energy
photons.
___ c) The scatter component in gamma camera images is located
at the high energy end of the photopeak.
___ d) Scatter does not affect the measurement of gamma camera
dead time.
___ e) Backscattered radiation affects image quality more than
low-angle scattered radiation.
9.
The following combination of quality control tests are to be carried out on
gamma cameras daily:
a)
field uniformity, linearity, spatial resolution
b)
field uniformity, photopeaking
c)
photopeaking, linearity, spatial resolution
d)
photopeaking, field uniformity, sensitivity
e)
photopeaking, field uniformity, linearity, spatial resolution
10.
The typical energy window used for imaging Tc-99m on gamma cameras is
a)
1%
b)
5%
c)
20%
d)
30%
e)
45%
11.
Answer True/False to the following statements.
a) The most important effects involved in producing
scintillations in a sodium iodide crystal include Compton effect and pair
production.
b)
Most gamma camera crystals are highly purified thallium iodide
(sodium).
c) Each stage of dynodes in a photomultiplier tube typically
increases the number of electrons by a factor of approximately 4.
d) When gamma rays strike the photoemissive surface,
photoelectrons are produced.
e)
The crystal in a gamma camera is usually about 1 inch thick.
f) The image quality obtainable with Xe-133 is better
than that obtainable with Tc when imaging with a scintillation camera.
12. The optimal
distance from the collimator to the patient's body surface for a scintillation
camera equipped with a parallel‑hole, multiaperture collimator is
a) ½ the collimator diameter
b)
one collimator diameter
c)
2 times the collimator diameter
d)
4 inches
e) contact
13. A
scintillation camera is equipped with a pin-hole collimator. As the subject to
be imaged is moved away from the pin-hole along the center axis, the count
rate:
a. increased rapidly
b. increases slowly
c. does not change
d. decreases
e. first increases, then decreases
14. If a photomultiplier tube has 10
dynodes and each has a multiplication factor of 4, what is the overall
photomultiplicative power of the tube?
a. 40
b. 104
c. 410
d. 10 x 42
e. 4 x 102
