The usefulness of indices measuring gamma camera non-uniformity

The following four quantitative measures of uniformity were assessed for flood images produced on an Ohio Nuclear Sigma 410 gamma camera by positioning a point source of sup(99m)Tc pertechnetate about 1.5 m from the uncollimated camera face: 1) the mean integral non-uniformity 2) the differential non-uniformity 3) the coefficient of variation of the counts per element 4) a measure of the width of the frequency distribution of the contrast between neighbouring elements. The agreement between the subjective ranking of the images and that based on one of the four uniformity indices was measured by Spearman's rank correlation coefficient. The coefficients are presented for each of six observers and for each of the four uniformity indices. With the exception of the comparison between integral uniformity values and the black and white analogue images, the objective measures of uniformity showed a significant correlation with the subjective assessments. (U.K.)