A prototype emission-transmission imaging system

The prototype imaging system developed can perform simultaneous X-ray transmission CT (computed tomography) and SPECT (single photon emission computed tomography) studies of phantoms and small animals. This system uses a small linear detector array which consists of a single high-purity-germanium crystal segmented by ion-implantation into 23 2-mm elements. The detector array and its associated electronics can sustain count rates up to 10/sup 6/ cps/element while maintaining sufficient energy resolution to discriminate between X-rays at tube potentials of 100-120 kV and higher-energy gamma -rays from /sup 99m/Tc and /sup 123/I. The data acquisition system supports two energy windows per channel and may be used for emission-transmission or dual-energy X-ray imaging. Initial studies have demonstrated that X-ray CT and SPECT images acquired with this device are spatially correlated and may be superimposed to localize the SPECT image on the transmission map. Preliminary data also show that it is possible to use dual-energy X-ray CT to derive an object-specific attenuation map at the radionuclide energy. This attenuation map may then be incorporated into an iterative reconstruction algorithm to yield significant improvements in SPECT quantitation.< >