Design simulations of a LSO crystal block detector module for dual PET/SPECT systems

Monte Carlo simulations were carried out in order to guide the choice of crystal block material and thickness for a small FOV PET/SPECT camera. A continuous crystal block of 50mm x 50mm was simulated considering several thickness (8 mm, 16 mm and 32 mm) and two scintillation crystal types(LSO:Ce and NaI:Tl). Detection module parameters like spatial resolution at centre and border of FOV, efficiency and energy resolution were evaluated. Despite there is a common opinion that LSO is a less valuable material for SPECT detection, our findings demonstrate that LSO crystal blocks have interesting design features for the development of an hybrid SPECT and PET system. Our results show that by adequate corrections of non-linearity of a thick crystal block response, a high detection efficiency can be preserved (nearly 80% for PET and 99.9% for SPECT) without compromising high spatial resolution (about 1.9 mm for PET and 1.45 mm for SPECT).