Methods for comparing the performance of different gamma cameras.

Meaningful comparisons of different gamma cameras require the acquisition of numerical data characterizing each of the characteristics of interest. These include resolution, contrast, sensitivity, uniformity, dead time (and the resulting percent loss), and the maximum counting rate. Resolution is best determined by using a line source to measure the linespread function, from which the modulation transfer function can be calculated. Bar patterns are useful in showing the effect on resolution of different collimators and different source distances. Sensitivity comparisons depend on collimator choice, and require counting the same object under identical conditions. Accurate comparisons of dead times and maximum counting rates require extreme care that measurements are taken under identical conditions of scatter, source volume, window setting, etc. Comparisons of the intrinsic dead times should be made with the collimator off, while actual counting losses should be determined using the collimators and appropriate phantoms. With today's high resolution and high-speed gamma cameras, the conditions under which a camera is used would appear to play a larger role in determining its performance than would the small differences in inherent capabilities between the cameras of various manufacturers.