Inter-Modular Synchronization in a TOF-PET System Using the Natural LYSO Background Radioactivity

Simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is a promising platform for clinical and research with applications in oncology, neurology, cardiology, and inflammatory diseases. One challenge for simultaneous PET/MRI is the mutual electromagnetic interference between the two imaging modalities. MR-compatibility is required for any system integrating with an MR scanner. It is difficult to achieve both time-of-flight (TOF) capability and MR compatibility using the standard inter-modular synchronization method that uses synchronization signals based on either optical fibers or electrical cables. In this paper, we propose a new method to achieve inter-modular synchronization for PET systems without additional electrical cables or optical fibers by using the natural background radiation present in lutetium-yttrium oxyorthosilicate (LYSO) scintillator crystals. We investigated the feasibility of the approach with two full detector modules comprising 1536 one-to-one coupled 3x3x20mm
³
LYSO crystal-silicon photomultipliers (SiPM) channels. Using the natural LYSO background radiation for synchronization resulted in a CTR of 274.6ps FWHM with a peak location at -13.8ps, compared to the re-calibrated (reference) results with a CTR of 271.1ps FWHM with a peak location at -10.3ps.