Measurement of the depth of interaction of an LSO scintillator using a planar process APD

The authors have evaluated the performance of an avalanche photodiodes (APD)/lutetium oxyorthosilicate (LSO) module for use in positron emission tomography systems. They have used a recently developed APD detector in combination with a 3 × 3 × 30 mm³ LSO scintillator to measure the depth of interaction of 511 keV photons from a ²²Na source. The detectors were built using standard planar technology for silicon devices. Photodiodes with 3 mm diameter active area have been produced by deep boron diffusion, followed by shallow boron and phosphor diffusion. Because the structure has not been optimized yet, the authors only obtained a gain of 6 at 1300 V. A simple noise analysis of the detector characteristics indicate that they are still capable of measuring 511 keV photons with sufficient energy resolution for depth of interaction position measurement from a long LSO scintillator.