INSERT Project: First results of a MR compatible preclinical SPECT based on SiPM photodetectors

We report on the results achieved with the first SPECT insert for general purpose MR scanners, developed within the INSERT project (INtegrated SPECT/MRI for Enhanced stratification of brain tumors in Radio-chemoTherapy). The present paper focuses on the implementation and performance assessment of a preclinical version of the SPECT. A clinical configuration is currently under development and will be optimized accordingly to the results from the preclinical system. The SPECT is composed by a full ring of gamma detection modules based on compact and MR compatible Silicon PhotoMultipliers (SiPMs). The intrinsic spatial resolution of the detection modules has been measured as 1.0 mm FWHM over 40 mm × 40 mm planar field of view (FOV), at 140 keV and at 4 °C. The energy resolution of the detector is 13.7 % for Tc-99m (140 keV, at 4 °C) and has been optimized to permit the simultaneous acquisition of multiple radiotracers. The main components, namely the detection modules, the collimator and custom RF coil, have been realized with a compact design to fit inside common MR bores. Moreover, mutual compatibility between SPECT system and MR has been studied and optimized for all the SPECT components. First tomographic images have been acquired from phantoms and in vivo animal models. The gamma detection modules have been tested in a 7 T MRI (MAGNETOM by Siemens) to measure induced disturbances on the electronic chain. The detection module negligibly affects MRI imaging. The outcomes of mutual compatibility tests provide enough confidence to proceed with the first synchronous SPECT/MR imaging experiments.