Evaluation of CdTe for use in a prototype emission/transmission CT imaging system

Cadmium telluride has been investigated for potential use in a prototype imaging system capable of acquiring both x-ray CT and SPECT data. The system is being designed to accumulate SPECT images with 140 keV gamma rays, thus requiring 4 mm detector thicknesses to achieve satisfactory stopping power. This study primarily investigates whether an alternative pixel orientation can be used with thick detectors to preserve the higher photopeak efficiencies normally associated with smaller thicknesses. Using 57Co (122 keV) as a substitute isotope to 99mTc, small 2 mm CdTe cubes were investigated along with edge irradiated 2 x 4 x 2 mm bars of both CdTe and CdZnTe. The photopeak efficiency of the large bars can be increased through the use of cooling but energy resolution remains less than desired. Small cubes of either material meet the resolution requirements, but the efficiency of patient dose would be sacrificed