The purpose of the dark noise CR lab was to make sure that the CR cassette didn’t not show any dark noise after being processed. This lab was completed by using a 10x12 CR cassette and a CR processing unit system to test the system noise. A cassette was chosen and erased using the processor. It was then reloaded into the processor without any exposure. A study was chosen at random and a “pattern” setting was chosen. The post processing image enhancements were disabled in order to visualize the image for uniformity of appearance. An exposure index of 20 was recorded which is considered a pass because it was under 80. Ideally, the image should have been completely uniform showing no signs of artifacts except for possible bands in the screen movement direction. However, after modifying the window width and window level, the image showed signs of black dots throughout. Depending on the brightness of the image, the dots disappeared and reappeared. The dark noise was also more visible when the magnification was increased to 50% and 100%. The system contained approximately 20 small dead pixels when the brightness was lowered. They appeared the same as the one seen below.
According to the AAMP, the required standards of EI<80, PV<80, PVSD<4 for general plates need to be met in order to pass the assessment. This would mean that because dark noise is present, the cassette did not pass the standards. This quality control test should be done regularly to ensure that the CR cassette being used doesn't have any dead pixels. If there are dead pixels that haven’t been discovered, a radiologist could confuse them for a pathology. This could cause a misdiagnosis for a healthy patient.
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