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内容記述 |
[Background] In preclinical small animal PET, high spatial resolution is essential for the accurate evaluation of tiny structures such as mouse brain and tumor microenvironment. In addition, a long axial field-of-view (FOV) is required for visualizing the whole-body pharmacokinetics at a single scan. Furthermore, a wide gantry bore (a wide ring diameter) is better for wide-range applications from rodent to non-human primate imaging. To meet these demands, we have developed a high-resolution and large FOV small animal PET, Mirai-PET. Its key feature is our original crosshair light-sharing (CLS) detector that can measure time-of-flight (TOF) and depth-of-interaction (DOI) information. This study reports the performance characteristics of Mirai-PET by phantom and animal imaging demonstration.[Methods] We selected Ce:LuxGd2-xSiO5 (LGSO) as a scintillator material because of its high detection efficiency and short decay time. Each crystal element size was 1.45×1.45×15 mm3 (scintillator pitch: 1.6 mm). A silicon photomultiplier (SiPM) of 8×8 array (3×3 mm2 pixel, 3.2 mm pitch) was connected to the 14×14 array of the crystals. Four crystals attached to a single SiPM pixel. DOI information was obtained from the output ratio of two neighboring SiPMs (Yoshida, et al. Biomed Phys Eng Express. 2023). The number of the detector block was 126, the ring diameter was 170 mm, and the axial FOV was 156 mm. All the components including the data acquisition system and a power supply unit were on a compact pushcart for portability, and the entire system can be moved by one person. Performance characterization was performed according to the NEMA NU4 and NU2 standards. Mouse and rat whole-body imaging and rhesus monkey brain imaging were conducted for demonstration. [Results] The spatial resolution at the near center was 1.4 mm with the filtered backprojection reconstruction. Some 0.75 mm rods and all 1.0 mm rods (even at the 50 mm offset) were resolved with the ordered-subset expectation-maximization reconstruction. The peak noise-equivalent count rate (NECR) was 103 kcps at 28.3 MBq for the mouse-sized scatter phantom. The TOF resolution was 231 ps. Total-body dynamic 18F-FDG uptake changes were visualized in mouse 18F-FDG imaging. In mouse and rat 18F-NaF imaging, the bone structures of the total-body uptakes in the mouse and the uptakes from the head to pelvis in the rat were clearly visualized. In monkey brain 18F-FDG dynamic imaging, the gray matters, striatum and putamen were identified with high contrast. [Conclusion] We developed the Mirai-PET: a high-resolution, portable and axially long FOV small animal TOF-DOI PET system. Excellent imaging performance for rodents and non-human primates were shown. |
