Performance results of a new DOI detector block for a high resolution PET-LSO research tomograph HRRT

To improve the spatial resolution and uniformity in modern high resolution brain PET systems over the entire field of view (FOV), it is necessary to archive the depth of interaction (DOI) information and correct for spatial resolution degradation. In this work the authors present the performance results of a high resolution LSO/GSO phoswich block detector with DOI capability. This detector design will be used in the new CTI High Resolution Research Tomograph, ECAT HRRT. The two crystal layer (19×19×7.5 mm³) and a light guide are stacked on each other and mounted on a (2×2) PMT set, so that the corners of the phoswich are positioned over the PMT centers. The crystal phoswich is cut into a 8×8 matrix of discrete crystals. The separation of the LSO and the GSO layer by pulse shape discrimination allows discrete DOI information to be obtained. The high light output and the light guide design results in an accurate identification of the 128 single crystals per block. Flood source measurements document a very good homogeneity of events, energy centroid stability and energy resolution (14-20% FWHM) per single crystal. An intrinsic resolution of ~1.3 mm and the DOI feasibility is extracted by coincidence measurements with a single GSO crystal