Engineering Aspects of a Hybrid Emission Computed Tomograph

A prototype of a hybrid emission computed tomograph was constructed and evaluated. The detector system consists of 64 NaI crystals located on a circle 42 cm in diameter. The system has two types of collimators, one for single photon counting (SPC) and the other for positron annihilation gamma ray detection (ACD). These two collimators are set inside the detector circle and one of them is selected by a motor driven axial shift mechanism. Finer data sampling is carried out by the combination of collimator movement and detector rotation (SPC mode), or by the combination of detector rotation and wobbling (ACD mode). The spatial resolution at the center of the image field was 10 mm FWHM for the SPC mode and 11 mm FWHM for the ACD mode. The measured sensitivity for a 20 mm thick slice was 20 kcps/(¿Ci/ml), 10 kcps/(¿Ci/ml), and 20 kcps/(¿Ci/ml) with a 20 cm cylindrical water phantom containing uniform activity of Tc-99m, Xe-133 and Ga-68 respectively. The fastest scanning time is 2 s. with a resolution of 24 mm FWHM.