Description of a prototype combined CT-SPECT system with a single CdZnTe detector

The authors have developed a system that performs both X-ray CT and SPECT using a single CdZnTe detector. Their prototype employs a 9.6×9.6-mm² CdZnTe detector with 1.5×1.5-mm² pixellated anodes configured as a 4×4 array. Pulse counting electronics with short shaping time (50 ns) are used to satisfy requirements for high photon rates in X-ray imaging, and to achieve response linearity up to 4×10⁵ counts per second per detector element. The measured energy resolution at 140 keV is 10.4%. The authors have characterized system performance by imaging a radiographic resolution phantom and the Hoffman Brain phantom. The spatial resolutions of CT and SPECT are about 1 mm and 9 mm, respectively. The sensitivity per detector area of radionuclide imaging is about one-half of that of a conventional imager. The registration of images from these two modalities is intrinsic since the imaging geometry is identical