A CdTe detector for hyperspectral SPECT imaging

A Cadmium Telluride (CdTe) detector has been developed for multiple-radioisotope SPECT imaging. The 2 x 2 cm detector has 80 x 80 pixels on a 250 mu m pitch and a three-side buttable design so that it can be tiled into larger arrays. The detector is termed hyperspectral as it measures the energy of every photon that interacts in the CdTe to give fully spectroscopic information from 5-200 keV in each pixel. The detector has been tested for applications in multiple-radioisotope SPECT imaging using a 1mm diameter pinhole configuration and standard phantom test objects containing Tc-99m, I-123 and Ga-67. The detector has an average pixel energy resolution (FWHM) of 0.75% at the I-123 photopeak of 159 keV. We demonstrate the system's capability of resolving spatial features of 2 mm, although the spatial resolution of the detector is limited only by the pixel size and pinhole magnification factor. These characteristics are superior to alternative detectors currently in use in clinical SPECT systems. When imaging multiple radioisotopes simultaneously, we show that there is very little cross-talk between adjacent photopeaks, leading to superior image contrast. The detector is also capable of resolving fluorescence x-rays from the radioactive source, which could be used to improve image count statistics or derive information about the attenuation properties of the source. The performance presented here, and the ability to tile the detector modules to create a clinically useful field of view, makes this technology a strong candidate to be used in future solid-state SPECT cameras.