Charge collection studies of a high resolution CZT-based detector for PET

Our team is developing the CZT Small Animal PET System, a 1-mm resolution imager for small animal studies. The techniques are also applicable to breast imaging with PET, and Compton imaging for gamma-ray surveillance and threat assessment. CZT detectors are used to achieve 2 – 3 % FWHM energy resolution at 511 keV, which strongly suppresses the effects of Compton scattering on image quality and quantification. The detectors are read out with a novel crossed-strip electrode technique that localizes interaction sites in two dimensions. In the third dimension, charge drift time and the ratio of cathode to anode signals are used for localization. With these capabilities and our electrode design, photon interaction sites are resolved into voxels measuring 1 mm × 1 mm transverse to the incoming direction of an annihilation photon and 5 mm parallel to it, which should enable 1 mm tomographic reconstructed spatial resolution in three dimensions. A steering electrode between the anodes improves charge collection and energy resolution. The detectors’ size is 39 mm × 39 mm × 5 mm and they are read out with RENA-3 ASICs. To study detector and ASIC performance, we developed the Evaluation System that contains four detectors and six RENA-3s. We describe the CZT Small Animal PET System, the Evaluation System, and the detector design. Then we report measurements of the detector’s spatial and energy resolution, the effect of the steering electrode on charge collection, and plans for the future.