The relationship of instrument parameters to performance within a survey peer group

Using simulators of transmission imaging, an interlaboratory survey assessed the discriminatory performance of 86 subscribers, each of whom imaged a liver phantom in anterior and right lateral projections. Analysis was by receiver operating characteristic (ROC) with Az, the area under the ROC curve, used as a measure of accuracy unconfounded by decision bias. Az values were then defined as the dependent variable in a statistical model that related performance to several instrument design and operating parameters. Six of 14 postulated parameters explained approximately half of observed subscriber variability. These were: year of camera manufacture or upgrade, number of photomultiplier tubes, collimator type, total counts collected, use of a Co-57 disk source for imaging the phantom, and computer processing of the image. The findings confirm previous inferences drawn from controlled intralaboratory experimentation, but hitherto unsubstantiated by clinical imaging data.