Design and first performance tests of the SAFIR-II PET-MR Scanner

SAFIR-II is a high-performance Positron Emission Tomography (PET) insert designed for a Bruker BioSpin 70/30 magnetic resonance imaging (MRI) scanner. It was designed to acquire images for mice and rats within 5 s. This is achieved by minimizing dead-time effects and widening bandwidth limitations, enabling image acquisition at high source activities of up to 500 MBq. Following the "Dual Ring Prototype" and SAFIR-I, SAFIR-II presents the finalized detector design. It employs 11.520 Lutetium-Yttrium oxyorthosilicate (LYSO) crystals (2.0 × 2.0 × 13 mm
³
) coupled one-to-one to Hamamatsu MPPC S13361-2050 silicon photomultiplier arrays (crystal pitch: 2.0 × 2.0 mm
²
) to cover an axial field of view of 144.3 mm. The SiPM’s analog signals are digitized using PETA8 Application Specific Integrated Circuits (ASICs), and then read out and transmitted to a DAQ-Computer using an FPGA (Xilinx Kintex7) and an optical 10 GBit Ethernet Link. MR-compatible DC-DC converters and low dropout voltage regulators are used to condition all internal low-voltages. The total power consumption is 558 W.In this work, we present an initial performance evaluation of the PET insert using low and high activity measurements. A point-source measurement at 2.6 MBq yielded a coincidence timing resolution of 217 ps (full width at half maximum (FWHM)) and a coincidence energy resolution of 11.8 % (FWHM, from Gaussian fit). Measuring a line-source phantom at 500 MBq showed a coincidence timing resolution of 277 ps and a coincidence energy resolution of 12.3 %.