Local energy scale map for NanoPET™/CT system

The PET component of NanoPET^TM/CT designed by Mediso Ltd. is a high resolution small animal PET system, in which every detector module contains 81??39 LYSO crystal needles of the size of 1.12??1.12??13 mm³. Two Hamamatsu H-9500 position sensitive photomultipliers (PSPMT-s) are optically coupled to the same crystal matrix using a thin BK-7 optical glass lightguide, allowing 95 mm AFOV. The gains of the 2??256 anodes of the PSPMTs are not uniform. The gap between the two PSPMTs results in restricted light collection efficiency for the crystal needles at the middle of the module. These two effects cause non-uniform gain, that could cause improper energy gating, the loss of 511 keV (photopeak) events and the imperfect filtering of the scattered photons. We have aimed to determine a local gain map for the detector to perform a uniformity correction to avoid these disadvantages. We have developed and implemented an application called LUT-QT to solve the crystal positioning and the gain uniformity correction pixel-by-pixel. Considering the large number of crystal elements in the detector ring (37908 pcs), all of the methods were designed to run automatically, although all of them allow the possibility of manual modification in every step. This method can be applied for every PET detector module based on pixelated scintillation crystal matrix and multianode PSPMT-s.