? The long term objective of this work is to develop a new technology for gamma-ray imaging cameras based on the combination of digital processing electronics and position sensitive avalanche photodiodes (PSAPDs). Gamma cameras are finding increasing applications in diverse medical fields ranging from SPECT cameras for emergency room cardiological screening through scintimammography cameras for detecting breast cancer to small animal cameras used in metabolic and drug development studies. Present cameras, constructed using position sensitive photomultiplier tubes and analog processing electronics are bulky, heavy, and expensive. We have developed a preliminary gamma camera design that uses solid state PSAPD detectors and high density digital processing electronics to create a compact camera design that will weigh only 10-20% of existing designs, have significantly improved imaging quality, and cost half as much. A preliminary analysis shows that, to reap these benefits, it is necessary to fully understand the PSAPD's electronic noise properties and design the processing electronics to maximize signal/noise in order to optimize spatial resolution and image quality. The Phase I effort will therefore be devoted to extensively characterizing a PSAPD's noise properties as a function of temperature and signal processing variables and making measurements with small scintillator arrays to determine achievable spatial resolution. The preliminary design will be turned into a complete design with specified parts and modeled and analyzed to accurately project both its performance characteristics and production costs. The Phase II effort would then consist of constructing a pair of gamma cameras based on the Phase I design: a 21 cm x 21 cm camera with 2 mm spatial resolution intended for cardiology work and a 10 cm x 10 cm camera with 1 mm intrinsic spatial resolution intended for small animal work. Both cameras would then be subjected to a wide variety of point source and phantom imaging tests to fully characterize and optimize their performance. ? ?
