PET performance evaluation of a RF-penetrable PET insert for simultaneous PET/MR imaging

Integrated PET/MRI enables simultaneous measurement of molecular, functional and anatomical information of the body in one combined scan, providing physicians and researchers with multi-parameter information. However, the long-term impact of integrated PET/MRI is limited by the high cost of the current commercial systems, which require the users to purchase both PET and MR subsystems, which are permanently integrated. We are developing a RF-penetrable PET insert technology to address this challenge, and a prototype brain-dedicated insert system has been built to evaluate the technology. The insert system consists of 16 detector modules assembled into a ring of an inner diameter of 32 cm. A total number of 2,048 3.2 mm × 3.2 mm × 20 mm LYSO crystals coupled one-to-one to 2,048 SiPM pixels are implemented in the system. An intrinsic spatial resolution of below 2.3 mm has been achieved by measuring the coincidence point spread functions of a 500 μm positron-emitting point source with two electronically collimated detectors. A custom resolution phantom with hot rods ranging from 2.8 to 5.2 mm diameter has been acquired and reconstructed to evaluate the image spatial resolution of the system. The sizes of the smallest resolvable hot rods in the reconstructed images were 2.8 mm and 4.2 mm, when the phantom was placed at the center of the fleld-of-view and 9-cm off-center trans-axially, respectively. An energy resolution of 15.6 % FWHM at 511 keV and a coincidence time resolution of 5.2 ns FWHM have been achieved, limited by the outdated 2008 SiPM technology employed. The variation of the energy resolution and coincidence time resolution stays within a range of 0.5 % and 80 ps over 3 hours, demonstrating the stability of the system.