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Biodex Medical Systems, Inc. © 2016 135
Figure 6.5. The Save Expanded Constancy Data Results screen.
Geometry Test
(See Figures 6.6 - 6.9.)
The Geometry Test is used to check if the system is correctly measuring the activity of a dose at
different volumes as the dose is diluted. This test is usually performed using Tc-99m but other
isotopes can be used if desired. Generally, a dose of a small volume is chosen to begin and
saline is added to change the volume without changing the activity.
“Geometry independence” means that the indicated activity does not change with volume or
configuration of the source material. This test should be done using a syringe that is normally
used for injections. The following test assumes injections are done with 3 ml plastic syringes,
and the radiopharmaceutical kits are made in 30 ml glass vials. If you do not use these, change
the procedure so that your syringes and vials are tested throughout the range of volumes
commonly used.
If a significant volume correction results from these procedures, the tests should be repeated to
verify. Atomlab Dose Calibrators have been tested for volume dependence in Beta measurements
which are expected to be worst case and the results were 0.13%/ml. (Reference: Accurate Dose
Calibrator Activity Measurement of Y-90 Ibritumomab Tiuxetan,” J. A. Siegel Et Al, J Nucl
Med, 2004, 45:450-454.)
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