A semiconductor gamma camera has long been a goal of nuclear medicine because semiconductor-detector arrays have better energy resolution and spatial resolution than scintillators. However, existing semiconductor detectors are expensive and are available only in small sizes. A new semiconductor material, ZnCdTe, is now available in large sizes with better uniformity of detector response and may eventually be much less expensive than existing semiconductor detectors. This project will test a new design approach that could sufficiently reduce the complexity of the readout electronics that construction of a ZnCdTe gamma camera would become economically feasible. However, individual detector components, not the entire camera, will be constructed to evaluate the following aims: To ascertain if pulse shape information can be used to estimate the location of the gamma-ray interaction with sufficient precision to allow a large reduction of the number of detector cells without a corresponding loss in resolution, to determine if good energy resolution is recoverable from the same pulse shape information. In order to fulfill these aims a precise model of the charge transport in each semiconductor detector will be derived from measured maps of the detector's properties. Alternatively, the maps will be used to derive lookup tables for position estimation. A new multiplex readout scheme with favorable noise properties will also be implemented. When a semiconductor modular SPECT system with high spatial resolution becomes available, it should be an important clinical advance. For instance, in brain imaging it will be useful for localizing the sites of focal epilepsy to guide surgical intervention and for assessing the location and extent of infarcts.
