Timing performance of pixelated CdZnTe detectors

In comparison with most medical imaging techniques, Nuclear Medical imaging has traditionally been plagued by inferior image quality as a result of th e limitations imposed by mechanical collimation, which is necessary to form an image using single-photon emitters. To a large extent, this basic limit ation may be overcome with the use of posit;on-emitting radiotracers to det ect the two photons that are emitted following positron annihilation. Altho ugh CdZnTe semiconductor detectors are renowned for their increased count-r ate capabilities and improved energy and spatial resolution, they have some limitations regarding timing and charge collection efficiency. The CdZnTe rise-time has two components: electrons, and hole-induced charge collection ; Since the holes move much slower than the electrons, and because there is an equal absorption probability at all depths and energies(in the region o f 511 keV), the different slopes between the rise rime and the timing signa l, vary dramatically. These slopes are mostly influenced by the 'small pixe l effect'. This effect is relative to the amount of charge collected and th erefore, a different pulse shape slope will be obtained for different charg es collected. The current study directly examines the timing limitations of measuring coincidence events in CdZnTe-pixelated detectors. The results sh ow that it is possible to use these detectors for positron emission applica tions. (C) 2001 Elsevier Science B.V. All rights reserved.