Physics Effects in Single-Photon Emission Computed Technology (SPECT) Detectors

Abstract

All imaging techniques involving x-rays and gamma-rays have limitations imposed by the detector technology. In single-photon computed emission tomography (SPECT) systems, those limitations lead to trade-offs between energy resolution, spatial resolution, field of view, and sensitivity. An ideal detector would have a large area with excellent stopping power and high count rate capability, in addition to excellent energy and spatial resolution. Semiconductor detectors are an emerging technology that have three of these ideal attributes: high stopping power, excellent energy and spatial resolutions. Traditional semiconductor detectors comprise a high-Z crystalline material sandwiched by two electrodes. The high density leads to the detectors high stopping power. The electrodes can be segmented into small strips or pixels for good spatial resolution. The x-ray or gamma ray photons undergoes direct conversion to electron-hole pairs yielding favorable statistics for estimating the energy of the interaction. There are inherent limitations in these detectors; two of which this work proposes to address. The first is the fluorescence phenomenon present in both CdTe and TlBr detectors. We investigate whether developing a forward model that includes photon-matter interaction, charge transport, and signal induction, can allow statistical estimation methods to improve fluence estimates in double-sided crossed strip detectors. The second topic concerns readout electronics for double-sided strip detector signals. A waveform-capture readout system was built for a prototype TlBr detector developed by Radiation Monitoring Devices, Inc. (RMD). The detector and its readout were characterized. We investigated the energy resolution and tested methods to improve it. We also assess the ability to estimate depth of interaction(DOI) by observing the different effects in the waveforms generated by electron and hole transport.