Quantitative assessment of field uniformity for gamma cameras

Objective criteria for judging the uniformity of field floods are developed and the effects of the energy window and scatter material on uniformity are examined. There is a highly significant correlation (p = 0.99) between a 14% difference in average count among adjacent photomultiplier tube regions and observer detection of detuned areas. Similarly, a 10% average count difference is not significantly recognized as a nonuniform area. Results indicate that there is a complex interaction between uniformity, energy window (15-30% symmetrical) and 0-7.6 cm of tissue-equivalent scatter medium interposed between the flood source and the collimator. Quantitation of the flood should be performed to indicate which regions need retuning.