Performance Evaluation of SimPET-X, a PET Insert for Simultaneous Mouse Total-Body PET/MR Imaging.

PURPOSE: In this study, a small animal PET insert (SimPET-X, Brightonix Imaging Inc.) for simultaneous PET/MR imaging studies is presented. This insert covers an 11-cm-long axial field-of-view (FOV) and enables imaging of mouse total-bodies and rat heads. PROCEDURES: SimPET-X comprises 16 detector modules to yield a ring diameter of 63 mm and an axial FOV of 110 mm. The detector module supports four detector blocks, each comprising two 4 × 4 SiPM arrays coupled with a 20 × 9 array of LSO crystals (1.2 × 1.2 × 10 mm3). The physical characteristics of SimPET-X were measured in accordance with the NEMA NU4-2008 standard protocol. In addition, we assessed the compatibility of SimPET-X with a small animal-dedicated MRI (M7, Aspect Imaging) and conducted phantom and animal studies. RESULTS: The radial spatial resolutions at the center based on 3D OSEM without and with the warm background were 0.73 mm and 0.99 mm, respectively. The absolute peak sensitivity of the system was 10.44% with an energy window of 100-900 keV and 8.27% with an energy window of 250-750 keV. The peak NECR and scatter fraction for the mouse phantom were 348 kcps at 26.2 MBq and 22.1% with an energy window of 250-750 keV, respectively. The standard deviation of pixel value in the uniform region of an NEMA IQ phantom was 4.57%. The spillover ratios for air- and water-filled chambers were 9.0% and 11.0%, respectively. In the hot-rod phantom image reconstructed using 3D OSEM-PSF, all small rods were resolved owing to the high spatial resolution of the SimPET-X system. There was no notable interference between SimPET-X and M7 MRI. SimPET-X provided high-quality mouse images with superior spatial resolution, sensitivity, and counting rate performance. CONCLUSION: SimPET-X yielded a remarkably improved sensitivity and NECR compared with SimPETTM.

Development and Initial Results of a Brain PET Insert for Simultaneous 7-Tesla PET/MRI Using an FPGA-Only Signal Digitization Method.

In study, we developed a positron emission tomography (PET) insert for simultaneous brain imaging within 7-Tesla (7T) magnetic resonance (MR) imaging scanners. The PET insert has 18 sectors, and each sector is assembled with two-layer depth-of-interaction (DOI)-capable high-resolution block detectors. The PET scanner features a 16.7-cm-long axial field-of-view (FOV) to provide entire human brain images without bed movement. The PET scanner early digitizes a large number of block detector signals at a front-end data acquisition (DAQ) board using a novel field-programmable gate array (FPGA)-only signal digitization method. All the digitized PET data from the front-end DAQ boards are transferred using gigabit transceivers via non-magnetic high-definition multimedia interface (HDMI) cables. A back-end DAQ system provides a common clock and synchronization signal for FPGAs over the HDMI cables. An active cooling system using copper heat pipes is applied for thermal regulation. All the 2.17-mm-pitch crystals with two-layer DOI information were clearly identified in the block detectors, exhibiting a system-level energy resolution of 12.6%. The PET scanner yielded clear hot-rod and Hoffman brain phantom images and demonstrated 3D PET imaging capability without bed movement. We also performed a pilot simultaneous PET/MR imaging study of a brain phantom. The PET scanner achieved a spatial resolution of 2.5 mm at the center FOV (NU 4) and a sensitivity of 18.9 kcps/MBq (NU 2) and 6.19% (NU 4) in accordance with the National Electrical Manufacturers Association (NEMA) standards.