Preliminary results on a small animal SPECT system based on H13700 PSMPT coupled with CRY018 array

In this paper, we describe a new single photon emission computed tomography (SPECT) device made up of two detectors (High Resolution System, HRS) integrated into a rotation structure suitable for preclinical imaging applications. The overall objective is to develop an improved scintigraphic system based on our previous detector having high spatial resolution. For this purpose, we have assessed the performance of the new position-sensitive photomultiplier tube (PSPMT) Hamamatsu H13700 with 256 anodes, which replaces the Hamamatsu H9500 model. The adoption of the new PSPMT required the development of a dedicated compact electronics: a new resistive chain readout was optimized and integrated with an ADC system. Moreover, the new detector was engineered from both the mechanical and the electronic point of view. In fact, the entire system was miniaturized in order to reduce the overall dimensions. Alternatively, to the LYSO scintillator used in the previous detector, we have evaluated the CRY018 scintillator crystal, which provides a high light output, a medium density, a short decay time and excellent energy resolution, obtaining high efficiency comparable with the LYSO scintillator. We assessed the detector with the H13700 coupled with LYSO and CRY018 crystals of the same size. The H13700 model shows better quantum efficiency on crystal emission light than the H9500, and besides, the light collection near the edges has improved. Moreover, the use of CRY018 is preferred over the LYSO matrix for issues related to the reduced natural radioactivity of ¹⁷⁶Lu. The experimental results were confirmed by an extensive evaluation carried out by GATE/GEANT4 Monte Carlo simulations. Finally, the performance results achieved, pave the way to the development of a Small Animal Imaging SPECT made up by two detectors based on the H13700 coupled with CRY018 crystal array.