Design, Performance Evaluation, and Modeling of an Ultrahigh Resolution Detector Dedicated for Simultaneous SPECT/MRI

In this article, we report design and preliminary performance evaluation of a CdTe detector module for use in an MR-compatible preclinical single-photon emission computed tomography system. The detector module consists of four CdTe detectors. Each of them has a CdTe crystal with a dimension of 1.125 cm \times 2.25 cm \times 2 mm (thickness). The crystal anode side is divided into 32 \times 64 square pixels with a width of 350 \mu \text{m} and attached to a custom-designed energy-resolved photon-counting (ERPC) application-specific integrated circuitry. The ERPC CdTe detector module has a median energy resolution of 7.0 keV across 8192 (4 \times 32 \times 64) pixels and 95% of the pixels have energy resolution better than 9 keV inside a Siemens clinical 3-T MR scanner; it has a median detection efficiency of 0.47 and 95% of the pixels have detection efficiency between 0.44 and 0.49; the detector spatial resolution enables one to observe the point response function (PRF) distortion caused by a 3T magnetic field. An analytical method has been developed to model this distortion and the corresponding modeled PRF has a root of mean-square error within 5%, compared to the experimental PRF.