Factors affecting gamma-camera non-uniformity

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Abstract
Evaluation of detector non-uniformity is the most common practice in present day nuclear medicine quality control procedures. The object of this investigation was, firstly, to study the effectiveness of four simple indices in measuring uniformity and, secondly, to study the effect of photon energy and the use of energy correction circuitry on camera uniformity. The measurements were performed on three cameras. All four indices showed a marked dependence on count density over a range of 1-30 million counts/image. The indices were significantly lower for images containing 30 million counts than for images containing up to 10 million counts. By acquiring images containing 5, 10 and 30 million counts on ten consecutive working days the daily variability of the indices was evaluated. It was found that the percentage standard deviation of the indices increased with increasing count density over the range tested. Using a computer-generated 'cold spot' artefact of the same size as a PMT, the sensitivity of the indices to degradations in camera uniformity was evaluated. The cold spot was detected most readily in the 30 million count images.

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