Effect of detector scatter on the decoding accuracy of a DOT 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 d etector module consisted of a 4x4 array of detector units. Each unit consis ted of a 2x2 block of 2x2x20 mm LSO crystals. The detector units use light sharing and ratio information to estimate DOI. The detector system consiste d of 24 detector modules. Positioning methods using different criteria to s elect Be first interaction point in a detector module to improve decoding a ccuracy were investigated (e.g., maximum energy, second maximum, minimum DO I). Selecting the detector unit corresponding to the minimum DOI provided t he best decoding accuracy for photons entering perpendicular to the detecto r. However, for photons entering at large angles of incidence (e.g., 30 deg rees) the maximum energy selection criterion performed the best The average DOI offset due to scatter within a detector unit was 1.7 mm. Detector scat ter only had a minimal effect on the image resolution of the simulated DOI detector system. It had a slightly larger effect on the quantitative recove ry of small regions of interest.