Evaluation of a planar process APD with a LSO scintillator to measure depth of interaction

We have evaluated the performance of an APD/LSO combination for use in PET systems. We have used a recently developed APD detector in combination with a 3 × 3 × 30 mm³ LSO scintillator to measure the depth of interaction from ²²Na photons. 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, we only obtained a gain of 6 at 1300 V. In spite of the low gain, we have obtained a resolution of 24 % with a single APD and the 3 × 3 × 30 mm³ scintillator. The energy spectra acquired using two APDs connected to the small sides of the scintillator depends on the position of interaction and varies from 25 to 50 %. The measurements allow to obtain the depth of interaction inside the crystal with an uncertainty of about 2 mm.