Instrumentation Quality Control Flashcards
Basic Q.C.
Energy (photo)peaking–check daily (uses cobalt sheet source which gives photo peak close to Tc)
(Or point source Tc if uncollimated)
Uniformity (floods)–check daily
Obtain total of 3-5 million counts
Quantitative value needs to be <5% (for integral and differential uniformity)
Linearity and Resolution (bar phantoms)–check weekly
At least 3-5 million counts
Sensitivity–check weekly
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Uniformity (Floods)
Also uses cobalt sheet source
ASNC guidelines are <5%, though preferred is <3%
Same for both uniformity parameters (Integral uniformity, which is global;
and Differential uniformity, which is regional)
What affects uniformity?
Malfunctioning PMT
Cracked crystal
Off-peak setting of pulse height analyzer
(? Floods is same thing as “Energy Correction”)
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Bar phantoms
Document max spatial resolution (and if changing over time)
And
Documents ability to image a straight line
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Sensitivity
How long does it take the system to acquire a preset specified number of counts, using a fixed source of fixed activity
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Center of Rotation (COR)
Check weekly or monthly
Checks alignment btw the true mechanical COR and where center is in electronic matrix of computer image
Use point source
Most commonly this is seen after technician servicing, when not reset
“Tuning-fork” artifact (if 180 degree camera)
(“Doughnut” if 360 degrees)
Looks same as MOTION ARTIFACT–i.e. sharp break in heart border btw septum and lateral wall on bottom row of images
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Ring artifact
Occurs from non-uniformity–? specifically from malfunctioning PMT
1 cold spot turned into ring on final reconstructions due to rotation of camera around
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Plexiglass Phantom
Check quarterly or annually
Use Tc source (cylinder)–10-20 mCi
Phantom has different sized holes/circles in it
Determines 3D (SPECT) contrast, resolution, and uniformity of the system
Much higher counts total than daily flood test of uniformity–
32 million counts
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High count extrinsic flood-field uniformity correction
Weekly?
30-60 (100) million counts
Based on this test, a flood field correction map is created, to correct non-uniformities in image
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GM counter (survey meter)
Check it daily to make sure it responds to a source of radiation (“constancy”–?)
You checked a known source with long half life at initial use, and record the measured counts per minute;
Check same source each day and the measured exposure rate (counts per minute) should be within 10% of expected (i.e. the initial rate measured at time of calibration).
(Check annually that it responds ACCURATELY, i.e. calibrate it)–
Don’t understand this
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Dose Calibrator
Check it more often than GM survey meter
Background check (background activity picked up?--ie contamination; done for each isotope setting you use in your lab DAILY
Constancy–DAILY
Check that the same source yields reproducible readings day after day.
Should be <5% (“of decay corrected accuracy readings”)…? from previous day reading
Linearity–QUARTERLY.
Use sleeve shielding source of varying thicknesses to simulate decay of isotope.
Measured values should be <5% of calculated
(“Linearity” bc assessing dose calibrator ability to accurately measure activity at low and high end of range, i.e. after short decay time, and longer decay)
Accuracy–ANNUALLY
Assay test isotope of known dose (activity)
Compare meter results to decay-corrected calculated activity
Should be <5% difference btw expected and measured dose (i.e. activity)
Geometry
Check at installation
Various volumes of Tc solution each having same activity–make sure can accurately detect regardless of volume;
should be within 5%
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