An MRI-compatible PET insert for whole body studies in rodents at high functional and anatomical resolution

The feasibility of performing high-resolution PET and high-field MRI simultaneously in rodents has been previously demonstrated in small-scale systems capable of imaging the rat brain and mouse. We are nearing completion of a larger scale PET system which will accommodate the whole rat and perform at 9.4 T with <2 mm PET resolution. The PET insert has inner/outer diameters of 13.5/20.6 cm, compact enough to fit within the gradient set of a Varian large-bore 9.4T MRI system while accommodating on the inside a commercial Insight birdcage coil for the rat. The resulting volume capable of simultaneous PET/MRI imaging is 7 cm in diameter and 5 cm axially. The 96 PET detectors are arranged in 4 rings of modular detector blocks, each with an array of 2 x 2 x 14 mm LYSO crystal coupled to a Hamamatsu APD array and read out by the RatCAP ASIC. Data acquisition is divided into 4 sectors, each handled by a local FPGA which communicates via Ethernet to the host PC. Offline data processing software is being developed to bin coincidences and determine physical corrections. Image reconstruction follows a listmode OSEM approach. The design of all hardware components is complete and prototypes of each have been fabricated. System integration is underway and initial performance of the system will be presented.