Evaluation of a combined array-planar crystal for gamma-ray scintillation imagers

Over the last few years our interest was dedicated to the development of small field of view imagers for Nuclear Medicine applications, particularly in Oncology. Some years ago, the authors have described an original scintillation gamma camera based on a matrix of 2×2 R5900-C8 Hamamatsu Position Sensitive PhotoMultiplier Tube (PSPMT) coupled to a scintillating array. The intrinsic spatial resolution obtained was adequate for high-resolution imaging applications. On the contrary, the prototype was affected by reduced performances at the borders between PSPMT. The subsequent introduction by Hamamatsu of the R7600 flange-less PSPMT family allowed to reduce the dead areas at the borders. Furthermore, Hamamatsu R7600-C12 model, improving the charge sampling with lower anode pitch, allows to improve the spatial resolution and to optimize the spatial response. Good performance was obtained with 2×2 R5900-C8 PSPMT array with a Combined Array-Planar Crystal (CAPC) geometry, designed by the authors. It consists of a planar crystal segmented in the top in a 15×15 array, 3 mm square pixel, 1 mm thick, and 0.25 mm gap. Hilger manufactured two CsI assemblies, Na and Tl doped, respectively, for this study.