Effect of detector scatter on the decoding accuracy of a DOI detector module

Monte Carlo simulation was used to study the effect detector scatter has on the decoding accuracy of a depth of interaction (DOI) detector module and on the quantitative imaging characteristics of a DOI detector system, The detector module consisted of a 4×4 array of detector units. Each unit consisted of a 2×2 block of 2×2×20 mm LSO crystals. The detector units use light sharing and ratio information to estimate DOI. The detector system consisted of 24 detector modules. Positioning methods using different criteria to select the first interaction point in a detector module to improve decoding accuracy were investigated (e.g., maximum energy, second maximum, minimum DOI). Selecting the detector unit corresponding to the minimum DOI provided the best decoding accuracy for photons entering perpendicular to the detector. However, for photons entering at large angles of incidence (e.g., 30 degrees) the maximum energy selection criterion performed the best. The average DOI offset due to scatter within a detector unit was 1.7 mm. Detector scatter did not affect the image resolution of the simulated DOI detector system; however, it did affect quantitative recovery of small regions of interest