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2.6 Contrast to Noise Ratio (CNR) Check
Chapter 2
Performance Criteria and Corrective Action
• Performance criteria: The new (weekly) image's S value must fall within +/- twenty percent of the baseline S value es-
tablished for the same mammography X-ray unit.
• Corrective Action: Repeat the test confirming 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 alternative de-
vice, replace it and repeat the test. If the new combination passes the test, patient imaging may continue using the sys-
tem.
Documentation
• Record this activity in the Table RT-S1 (MEDICAL PHYSICIST'S MAMMOGRAPHY QC TEST SUMMARY).
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