NEMA NU 4-2008 performance and MRI-compatibility study of the edgeless preclinical PET insert: ScintoTube.

The goal of this work is to evaluate the performance of a preclinical Positron Emission Tomography (PET) system, named ScintoTube, which was constructed using a continuous (edgeless) LYSO:Ce scintillator. The PET compatibility tests with high-field Magnetic Resonance Imaging (MRI) scanners are also reported. Approach: We constructed a preclinical PET system based on a single, continuous-annular LYSO:Ce scintillator, with inner and outer diameters of 64 mm and 80 mm, respectively, and an axial coverage of 96 mm. The system has 24 virtual detectors, being each one composed of a matrix of 9×9 Silicon Photomultipliers (SiPMs). A novel trigger topology was implemented to retrieve the entire Light Distribution (LD) profiles. This information was used to provide the 3D photon impact coordinates which included the Depth Of Interaction (DOI) information. To evaluate the ScintoTube performance, the NEMA NU 4-2008 protocol was followed. Dead Time and quantification corrections were implemented in the reconstruction process. Moreover, since the system is intended to be used as an insert for high-field MRI scanners, it was evaluated when working under the influence of 7T and 9.4T MRI scanners by acquiring data with different MRI sequences. Results: This work successfully implements the edgeless concept for small animal PET insert and demonstrates that it is possible to retrieve homogeneous 3D photon impact positioning accuracy (in the 1 mm range) across the axial Field Of View (FOV) by using an edgeless design. The reported results also validate the capabilities of the PET insert to work under the influence of high-field MRI. There is almost no influence of the MR in our PET insert regarding spatial and energy resolutions and photopeak position. All PET parameter deviations are within the ±5% range when compared to non-MRI case. Significance: Overall, the obtained results show that the designed ScintoTube is a promising system to be used as an insert with unique capabilities such as fully characterizing the entire LD profiles (3D positioning), suppressing edge effects in the transaxial and axial directions, and improving sensitivity.