Analytical model for SPECT detector concepts

Pixellated cadmium-zinc telluride (CZT) detectors, providing higher spatial resolution and energy resolution than current gamma cameras, will improve the image quality of SPECT detector systems. Their performance has to be evaluated in terms of resolution, detector efficiency and image quality in a similar way as has been done earlier for NaI detectors. We have developed an analytical model for spatial resolution and geometric efficiency of collimators specifically for pixellated CZT based detectors. We derive an exact description for a variety of static and rotating detector concepts, use standard performance criteria for detection efficiency, and adapt measures for spatial resolution of pixellated detectors, based on the sampling of the single pixel response function (SPRF). The concept is extended to enable a comparative description of continuous scintillator based SPECT cameras. Tradeoffs among resolution, efficiency, signal-to-noise ratio (SNR) and minimum detectable contrast have been investigated for different detector concepts. Our analysis shows that concepts using rotating collimators suffer from noise accumulation, except for purely hot spot imaging. A finite optimization of current SPECT systems can be done based on this analytical model, and a further increase in image quality will be achieved by the higher spatial resolution and energy resolution of solid-state detectors.