Position mapping, energy calibration, and flood correction improve the performances of small gamma camera using PSPMT

The purpose of this study is to improve the performances of a small gamma camera using position sensitive PMT (PSPMT) by applying position mapping, energy calibration, and flood correction. The small gamma camera consists of a 5" PSPMT coupled with either CsI(Tl) array or NaI(Tl) plate crystals. Flood images were obtained intrinsically in CsI(Tl) array system and with lead hole mask in NaI(Tl) plate system. The position mapping was performed by locating crystal arrays and hole positions in the two systems. The energy calibration was performed using energy discrimination table for each pixel array or for each hole position. The flood correction was performed using a uniformity correction table containing the relative efficiency of each image element. The resolution of the CsI(Tl) array system remained similar before and after corrections. On the other hand, the resolution of the NaI(Tl) plate system was improved about 16% after correction. The uniformity and linearity improved 33.9% to 11.6% and 0.5 mm to 0 mm, respectively, in the CsI(Tl) array system. The corrections more effectively improve the uniformity and linearity in the NaI(Tl) plate system, 21.3% to 9.2% and 0.5 mm to 0 mm, respectively. Furthermore, the resolution deterioration observed in the NaI(Tl) plate system at the outer part of FOV, was considerably diminished after the corrections. The results of this study indicate that the correction algorithms considerably improve the performances of a small gamma camera and the performance gain is more prominent in the system employing a plate type crystal.