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

Abstract

(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 7T Magnetic Resonance Imaging (MRI) system. It is designed explicitly for high-rate kinetic studies in mice and rats with injected activities reaching 500MBq, 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 54.2mm and an inner diameter of 114mm. 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 separate-uncertainty 209.0(3)ps and separate-uncertainty 12.41(02) Full Width at Half Maximum (FWHM) at low activity and separate-uncertainty 326.89(12)ps and separate-uncertainty 20.630(011) FWHM at 550MBq, respectively. The peak sensitivity is ∼1.6. The excellent performance facilitated the successful execution of first in vivo rat studies beyond 300MBq. Based on features visible in the acquired images, we estimate the spatial resolution to be ∼2mm 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 500MBq.

SAFIR-I: first NEMA NU 4-2008-based performance characterization

“…The Small Animal Fast Insert for MRI (SAFIR) collaboration is developing novel Positron Emission Tomography (PET) inserts for a Bruker BioSpec 70/30 Ultra Shield Refrigerated (USR) Magnetic Resonance Imaging (MRI) system [ 1 , 2 ]. The inserts are specified to enable quantitative, truly simultaneous PET/MRI research in mice and rats, with a spatial resolution of around in the center of the Field Of View (FOV), at injected activities extending up to .…”

“…The inserts are specified to enable quantitative, truly simultaneous PET/MRI research in mice and rats, with a spatial resolution of around in the center of the Field Of View (FOV), at injected activities extending up to . Exploitation of the associated high count rates, specifically the corresponding low noise, enables an exceptional image frame acquisition speed in the order of one diagnostically relevant frame every few seconds [ 1 , 3 , cf.]. This high frame rate is required for capturing fast tracer kinetics, which was not possible with existing small-animal PET systems [ 1 , cf.].…”

“…Exploitation of the associated high count rates, specifically the corresponding low noise, enables an exceptional image frame acquisition speed in the order of one diagnostically relevant frame every few seconds [ 1 , 3 , cf.]. This high frame rate is required for capturing fast tracer kinetics, which was not possible with existing small-animal PET systems [ 1 , cf.].…”

“…A first insert, Small Animal Fast Insert for MRI detector I (SAFIR-I), has successfully been constructed and commissioned [ 1 ]. In this study, fundamental performance parameters of SAFIR-I have been determined according to the NEMA Standards Publication NU 4-2008 (NEMA-NU4) protocol.…”

“…The data processing including all calibration steps is described in [ 1 , 4 ]. Coincidences are saved in listmode files subsequently used for reconstruction and data analysis according to NEMA-NU4.…”