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2.6 Contrast to Noise Ratio (CNR) Check
Chapter 2
11
Exit the Analysis Tool.
– Select [File (F)], and then select the [Exit(X)] from the sub menu. The Analysis Tool screen is closed.
IMPORTANT
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• Maintain a consistent exposure technique at all times. Use an AEC mode that varies only mAs, and does not allow variations
in kVp, target and lter material.
• When performing this test, always wait the same length of time between exposure and processing of the plate. Always erase
the REGIUS plates before running this test. Each mammography X-ray unit will produce a unique CNR baseline value.
Compare weekly test results only against the baseline values of the same unit.
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HINT
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• When establishing the baseline CNR value, repeat the process, from Step 5 through Step 11, four more times. Calculate the
average of the ve CNR values and +/- 20% values, and record them in the Table RT-1 (Baseline CNR Value).
• The CNR value can be calculated by using a measurement tool of a diagnostic review workstation, instead of using the User
tool of REGIUS Console CS-3/CS-7. In that case, process the cassettes under the CNR-WS exam tag and send the image
to the diagnostic review workstation.
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2.6.6 Performance Criteria and Corrective Action
Performance criteria: The new (weekly) image's CNR must fall within +/- twenty percent of the baseline CNR estab-
lished for the same mammography X-ray unit.
Corrective Action: Repeat the test conrming that all technique factors and correct. If problems persist, the results
should be reported immediately to the medical physicist for further evaluation.
The source of the problem shall be identied and corrective action shall be taken on the component(s) that caused
the failure, before further patient imaging is performed. If the problematic component can be replaced by an alterna-
tive device, replace it and repeat the test. If the new combination passes the test, patient imaging may continue us-
ing the system.
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