Monte Carlo simulations of the GE discovery alcyone CZT SPECT system

Abstract

Compact SPECT systems with cadmium zinc telluride (CZT) solid-state detectors with improved energy resolution and shorter acquisition times have recently been introduced. These systems have, however, different energy characteristics compared to NaI(Tl) crystal-based cameras. There is therefore a need to develop new simulation models for these cameras. We modeled the charge transport within the CZT detectors for a GE Discovery 530c/570c SPECT system with multiple pinhole collimators employing the SIMIND Monte Carlo program and validated simulations against measurements. The incomplete charge collection between the anode and cathode in the pixilated CZT was modeled with the Hecht equation. The simulation also included charge-sharing effects across pixels due to physical interactions and charge diffusion. To validate our CZT-model 99mTc and 123I point sources and a 201Tl line source were acquired and measured energy spectra were compared with simulated energy spectra. The Monte Carlo simulated energy spectra agreed well with the experimental measurements within the photopeak, overestimated the k-edge x-ray escape peaks of Cd and Te, and slightly underestimated the remainder of the tail. Comparisons for a cardiac insert with a defect in an elliptical Data Spectrum phantom were also performed. Here, simulated projections were read into the GE Xeleris system for reconstruction. We found good agreement in image reconstruction visually. We conclude that it is feasible to simulate CZT detectors with good agreement using the SIMIND code.