Optimization of dual layer phoswich detector consisting of LSO and LuYAP for small animal PET

Dual layer scintillators for small animal PET have been developed to measure the depth of interaction and to improve resolution performances. The aim of this study was to perform simulations to optimize the order and length of each crystal composing the dual layer phoswich detector. A simulation tool GATE was used. The bases of our small PET were dual layer phoswich detector modules arranged in a ring with a 10 cm diameter. Each module consisted of 8 × 8 arrays of LSO and LuYAP crystals with 2 mm × 2 mm sensitive area coupled to a Hamamatsu R7600-00-M64 PSPMT. The length of the front layer varied from 0 to 10 mm with 1 mm intervals while the total length (LSO + LuYAP) was fixed to 20 mm. The order of the crystal layers of phoswich detector was also changed. The radial resolutions were kept below 3.4 mm and 3.7 mm over 8 cm FOV and sensitivities were 7.4% and 8.0% for LSO 5 mm-LuYAP 15 mm and LuYAP 6 mm-LSO 14 mm phoswich detector, respectively. While the high and uniform resolutions were achieved by using the LSO front layer, the higher sensitivity was obtained by changing the order of crystals. Feasibilities for applying crystal identification methods to phoswich detector consisting of LSO and LuYAP were approved by simulation and experimental measurement of light outputs of each layer of phoswich detector. In this study, the optimal order and lengths of dual layer phoswich detector were derived to achieve high sensitivity and high and uniform radial resolution.