Performance evaluation of gamma ray imaging devices for tumor detection: Choosing the optimal design.

Abstract

This dissertation is about performance analysis of gamma-sensitive intraoperative probes used for tumor detection in nuclear medicine. Small (<1 cm diameter) tumors, often undetected by external imaging and by the standard surgical inspection with sight and touch, can be found with probes. Simple calculations and measurements with radioactive tumor models show that small tumors should be detected by single-element probes, but often such probes fail to detect these small tumors in practice. This discrepancy is often caused by the use of a uniform background to predict probe performance. Real backgrounds are nonuniform and can decrease probe performance dramatically. Dual-element, coincidence, or imaging probes may solve the background problem, but they must be evaluated to determine their efficacy. We describe a method to predict probe performance in a realistic background which includes variations in normal organ uptakes. The procedure includes a calculated point-response function, a numerical torso phantom, and measured human biodistributions of a monoclonal antibody. The Hotelling Trace Value, a quantitative measure of tumor-detection performance, is computed from the probe responses in simulated studies. We calculated probe performance for various collimator configurations, backgrounds, and tumor sizes. We also measured the effect of comparing probe data from a tumor-detection site with data from a corresponding known normal site. We conclude that those probes with inherent background suppression, the dual probe and coincidence probe, have better tumor-detection performance than the single-element probe, even when data from normal sites are available. The imaging probe, although also designed with inherent background suppression, is inefficient and thus has poor performance at clinically feasible exposure times.