SAFIR-I: Design and Performance of a High-Rate Preclinical PET Insert for MRI

(1) Background: Small Animal Fast Insert for MRI detector I (SAFIR-I) is a preclinical Positron Emission Tomography (PET) insert for the Bruker BioSpec 70/30 Ultra Shield Refrigerated (USR) preclinical 7 [Formula: see text] Magnetic Resonance Imaging (MRI) system. It is designed explicitly for high-rate kinetic studies in mice and rats with injected activities reaching 500 [Formula: see text] [Formula: see text] , enabling truly simultaneous quantitative PET and Magnetic Resonance (MR) imaging with time frames of a few seconds in length. (2) Methods: SAFIR-I has an axial field of view of [Formula: see text] [Formula: see text] [Formula: see text] and an inner diameter of 114 [Formula: see text] [Formula: see text]. It employs Lutetium Yttrium OxyorthoSilicate (LYSO) crystals and Multi Pixel Photon Counter (MPPC) arrays. The Position-Energy-Timing Application Specific Integrated Circuit, version 6, Single Ended (PETA6SE) digitizes the MPPC signals and provides time stamps and energy information. (3) Results: SAFIR-I is MR-compatible. The system’s Coincidence Resolving Time (CRT) and energy resolution are between [Formula: see text] [Formula: see text] [Formula: see text] and [Formula: see text] Full Width at Half Maximum (FWHM) at low activity and [Formula: see text] [Formula: see text] [Formula: see text] and [Formula: see text] FWHM at 550 [Formula: see text] [Formula: see text] , respectively. The peak sensitivity is ∼ [Formula: see text]. The excellent performance facilitated the successful execution of first in vivo rat studies beyond 300 [Formula: see text] [Formula: see text]. Based on features visible in the acquired images, we estimate the spatial resolution to be ∼2 [Formula: see text] [Formula: see text] in the center of the Field Of View (FOV). (4) Conclusion: The SAFIR-I PET insert provides excellent performance, permitting simultaneous in vivo small animal PET/MR image acquisitions with time frames of a few seconds in length at activities of up to 500 [Formula: see text] [Formula: see text].