Performance of a PET Insert for High-Resolution Small-Animal PET/MRI at 7 Tesla

• Published in: Journal of Nuclear Medicine Vol. 59; no. 3; pp. 536 - 542
• Main Authors: Stortz, Greg, Thiessen, Jonathan D., Bishop, Daryl, Khan, Muhammad Salman, Kozlowski, Piotr, Retière, Fabrice, Schellenberg, Graham, Shams, Ehsan, Zhang, Xuezhu, Thompson, Christopher J., Goertzen, Andrew L., Sossi, Vesna
• Format: Journal Article
• Language: English
• Published: United States Society of Nuclear Medicine 01.03.2018
• Subjects: Algorithms; Animals; Arrays; Brain; Cerium; Crystals; Field of view; Image Processing, Computer-Assisted; Interference; Lutetium; Magnetic resonance imaging; Magnetic Resonance Imaging - instrumentation; Neuroimaging; NMR; Nuclear magnetic resonance; Phantoms, Imaging; Photomultiplier tubes; Positron emission; Positron emission tomography; Positron-Emission Tomography - instrumentation; Rodents; Scintillation counters; Signal-To-Noise Ratio; Spatial discrimination; Spatial resolution; Substructures (crystalline); Tomography; Yttrium; PET/MRI; image reconstruction; instrumentation; SiPM; molecular imaging; animal imaging
• ISSN: 0161-5505; 1535-5667; 2159-662X; 2159-662X; 1535-5667
• DOI: 10.2967/jnumed.116.187666

We characterize a compact MR-compatible PET insert for simultaneous preclinical PET/MRI. Although specifically designed with the strict size constraint to fit inside the 114-mm inner diameter of the BGA-12S gradient coil used in the BioSpec 70/20 and 94/20 series of small-animal MRI systems, the insert can easily be installed in any appropriate MRI scanner or used as a stand-alone PET system. The insert consists of a ring of 16 detector-blocks each made from depth-of-interaction-capable dual-layer-offset arrays of cerium-doped lutetium-yttrium oxyorthosilicate crystals read out by silicon photomultiplier arrays. Scintillator crystal arrays are made from 22 × 10 and 21 × 9 crystals in the bottom and top layers, respectively, with respective layer thicknesses of 6 and 4 mm, arranged with a 1.27-mm pitch, resulting in a useable field of view 28 mm long and about 55 mm wide. Spatial resolution ranged from 1.17 to 1.86 mm full width at half maximum in the radial direction from a radial offset of 0-15 mm. With a 300- to 800-keV energy window, peak sensitivity was 2.2% and noise-equivalent count rate from a mouse-sized phantom at 3.7 MBq was 11.1 kcps and peaked at 20.8 kcps at 14.5 MBq. Phantom imaging showed that features as small as 0.7 mm could be resolved. F-FDG PET/MR images of mouse and rat brains showed no signs of intermodality interference and could excellently resolve substructures within the brain. Because of excellent spatial resolvability and lack of intermodality interference, this PET insert will serve as a useful tool for preclinical PET/MR.