Reduced counts during a simulated extrinsic uniformity on a SPECT gamma camera.

Objectives: In order to ensure and maintain the best imaging quality on the gamma camera, routine quality must be performed. Quality control functions as a proactive measure to ensure the proper function of the gamma camera. As a technologist, if quality control is not preformed, an imaging study may not accurate and a diagnosis of a patient may be incorrect. Uniformity tests the function of the photomultiplier tubes, collimator, and detector efficiency, the goal being homogeneous count distribution in the image. To do this a radioactive sheet is placed on camera, the technologist would set the counting parameters to detect 5 million counts 1. During a simulated lab experience, the question was could there be less counts acquired during the extrinsic uniformity test and still pass quality control?

Methods: A Cobalt 57 source is placed on the gamma camera prior to an extrinsic flood being taken. Testing three acquisitions, one with 100,000 counts, one with 500,000 counts and one with 1 million counts. At each of the counting parameters, the uptake will be assessed for uniformity analysis.

Results: The source was checked at 100,000 counts, but there were not enough counts to pass uniformity analysis for the day. The same source was then checked at 500,000 counts, but the daily quality control was still found to be inclusive. Checking that same source at 1 million counts, gave the most information but still did not relay enough data to give an accurate assessment for uniformity analysis.

Conclusions: Due to the predetermined amount of counts allowed, the gamma camera did not pass quality control for the day. As time elapsed the count rate could not go above 1 million counts, leaving the study inconclusive on its assessment of the collimator, photomultiplier tubes, and detector efficiency.