Outcome 6 - Planar Gamma Camera Flashcards
what are the three routine QC?
- peaking
- uniformity flood
- spatial resolution
what is peaking?
ensuring that the RN used has its photopeak centred in the PHA
when do we peak?
ideally, every morning FOR EACH isotope BEING USED THAT DAY
what is auto peaking?
where the user doesn’t have to do anything and the equipment auto-tracks and finds the window appropriately on its own
is variance day-to-day normal for peaking? if so, why?
it is normal
it is due to the fact that there could be high voltage supply fluctuations
peaking can only be done extrinsically. t/f
false.
it can be done both intrinsically and extrinsically
during peaking, the source must be exposed to (part of/the entire) FOV.
source must be exposed to the entire FOV
for dual headed systems, variance between the heads shouldn’t occur. t/f
false.
variance can occur but not more than a few keV
uniformity flood
evaluating the field uniformity
(is the camera displaying a uniform flux of photons?)
which qc is the most sensitive indicator for camera performance and stability?
uniformity flood
for flooding, in terms of collimator use, extrinsically means? intrinsically means?
extrinsically = collimator on
intrinsically = collimator off
for flooding, in terms of source use, extrinsically uses? intrinsically uses?
extrinsic = fillable liquid flood or solid Co-57 source
intrinsic = small point source (~37 MBq)
during intrinsic uniformity floods, how far should the source be placed?
at least 5x the largest camera dimension
BUT 2m is sufficient
during extrinsic uniformity floods, how far should the source be placed?
can be placed directly on the collimator
or 10-15 cm above
what matrix size do we use for uniformity flood?
256 x 256
how many counts for intrinsic uniformity floods?
5-10M
how many counts for extrinsic uniformity floods?
10M
consideration for uniformity flood,
frequent test (whether it is intrinsic or extrinsic), the other is done on a less frequent basis. What is the frequency?
weekly or monthly
what is wrong with using a plexiglass phantom for uniformity floods?
it has issues with filling, air bubbles and has a tendency to bulge
what is the frequency of doing uniform floods with RNs that is also used on the camera?
at least quarterly
what does doing uniform floods with RNs that is also used on the camera verify?
- uniformity of the system with these RNs
- checks isotope-specific uniformity correction maps
can uniformity be evaluated qualitatively as well as quantitatively?
yes.
qualitative eval of uniformity
visually looking at the image for structured patterns and artifacts
quantitative eval of uniformity
- integral uniformity
- differential uniformity
we want results from the quantitative eval of uniformity to be under what %?
5%
integral uniformity
searches entire flood
max and min ct/pixel values
what do higher numbers in an integral uniformity indicate?
worsening uniformity
differential uniformity
searches short segments of the flood
highest/lowest ct/pixel values in a 5-pixel segment
UFOV (useful field of view)
95% of exposed crystal face
CFOV (central field of view)
center 75% of the UFOV
integral uniformity formula
(max cts/pixel - min cts/pixel)/(max cts/pixel + min cts/pixel) * 100%
differential uniformity formula
(high - low)/(high+low) * 100%
what results are desirable for integral uniformity? is it different for spect imaging?
between 1-5%
SPECT - ≤ 3%
which QC is considered semi qualitative?
spatial resolution due to the finite bar widths
how do we perform a spatial resolution QC?
with a four-quadrant bar phantom
how do we determine that spatial resolution is good in both X + Y directions?
by rotating the 4-quad bar phantom 3 times (180d, flip, then another 180d)
**imaged 4 times
is spatial resolution done extrinsic or intrinsic?
can be done either ex or in.
frequency for spatial reso test?
weekly
describe the procedure for intrinsic spatial reso.
- collimator off
- phantom placed on the detector
- Tc-99m point source centred over phantom
what count rate is required for intrinsic spatial reso?
10,000 to 40,000 cps
(3 to 5M count image acquired)
what matrix size is used for intrinsic spatial reso?
512 x 512
describe the procedure for extrinsic spatial reso.
- collimators on
- sheet source on collimator
- 4-quad bar phantom on top of sheet source
moire pattern
interference pattern that results when the width of the bars approach the collimator hole diameter
moire pattern more common in?
high sensitivity and med/high energy collimators
linearity
ability to produce a straight line
deviation in linearity of 0.4mm may produce non-uniformities of?
8%
what is used to evaluate linearity?
bar phantom
what are some non-routine QC tests?
- pixel size determination
- sensitivity check
- collimator integrity
- multiple-window spatial registration
- count rate capabilities
how is pixel size determination done?
- with two 10 cm lines drawn in a right angle on a cardboard + drop of activity is placed at the ends of each line
- put cardboard on camera, aligning the lines with the x + y axes
- draw count profiles to include both point sources at ends of one of the lines and repeat with the second line
- distance between 2 peaks measured in pixels = 10 cm
sensitivity check is done (extrinsically/intrinsically)
extrinsically
how are sensitivity checks done?
- 1-2mCi Tc-99m diluted to 3mm depth in a petri dish
- 10 count measurements performed at 60 secs each + one 60 sec background
how are sensitivity checks expressed?
cpm/uCi
sensitivity checks expresses the sensitivity of the _____ opposed to system
collimator
frequency of sensitivity checks
quarterly or semi-annually
residual measurement of activity is needed for sensitivity checks. what is that?
when you measure your syringe with the activity initially, empty it into the Petri dish and then measure the syringe again.
this is to see how much you actually transferred into the dish
sensitivity checks need to reproduced (varying/same) conditions each time
same conditions
in multi-head systems, no more than ___% difference in sensitivity between heads.
5%
collimator integrity
ensures gamma rays entering crystal are essentially parallel
how do we perform the collimator integrity test?
- taping the source to wall (should be 20 ft away from camera)
- reposition source to check entire collimator face
how many counts in the image do we need to acquire for collimator integrity?
1-2.5M
frequency of collimator integrity testing
monthly, quarterly or biannually
good results for a collimator integrity test?
radially symmetric area of activity
Multi-window spatial registration
checking to see if events in all windows are being assigned to the same location
how is multi-window spatial registration done?
- 4 drops of multi-energy isotope on a cardboard phantom
- imaging each window separately
- subtracting the resulting images from each other
frequency of multi-window spatial registration test
3-6 months
isotopes used for multi-window spatial registration
In-111 or Ga-67
count rate capabilities
dead time measurement and done during acceptance testing
how is count rate capabilities tested?
two-source method
- determination of count rate of source 1 alone, source 2 alone and source 1 + 2 combined in a phantom that simulates tissue scattering
NEMA standards
measures of performance + methods used for eval/comparing gamma cameras to one another
acceptance testing
- verifies that the system installed meets the vendor specifications
- verifies proper environment (temp, airflow, electric power)
benchmark testing
done immediately after institution accepts the camera + after major service
all routine QC tests performed and gives standard to what future qc is compared to
you can look for signs of crystal hydration by performing?
off-peak flood analysis
test that determines the size of a single pixel within the FOV with 10cm lines drawn at a right angle?
pixel size determination
how many images must be acquired to ensure spatial resolution is good in both X + Y directions?
4 images
test where point source is taped to wall to see radially symmetric area of activity across collimator face?
collimator integrity
test which is essentially a dead-time measurement
count rate capabilities
uniformity flood should have at least
2-6M counts
Done upon camera installation and verifies that the system installed meets the vendor specifications.
Acceptance testing
types of tests must be performed before cameras can leave the factory and are deemed “minimum acceptable standards”
NEMA standards
