Studies with a prototype high resolution PET scanner based on LSO-APD modules

Lutetium oxyorthosilicate (LSO) scintillation crystals coupled to avalanche photodiodes (APDs) have been proven to be an interesting detector module for high resolution positron emission tomography (PET). Compact detector modules were built to test their performance in a prototype tomograph. Each detector module consisted of sixteen 3.7 x 3.7 x 12.0 mm(3) LSO crystals, which are one-to-one coupled to a two dimensional APD array (2 x 8 diodes, 3 mm circle divide, 4 mm spacing). The signals were read out by a low noise, fast, charge sensitive preamplifier, a 50 ns shaping amplifier and CAMAC electronic modules. Two detector modules were mounted on a rotatable gantry, to simulate a detector ring. Long term runs over 110 hours have shown that the detector remains stable over a long period of time. The energy resolution (FWHM) was 13.4 % for 511 keV gamma rays and the intrinsic spatial resolution was 2.2 mm (FWHM). The gain dependence of the APD on temperature had been determined as 3.5 %/K. The time resolution was 3.2+/-0.1 ns (FWHM). Phantom measurements showed the suitability of the new LSO/APD detector for high resolution animal PET.