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Micro Insert: A Prototype Full-Ring PET Device for Improving the Image Resolution of a Small-Animal PET Scanner

¹ Mallinckrodt Institute of Radiology, Washington University in St. Louis, St. Louis, Missouri; ² Institute of Modern Physics, Chinese Academy of Science, Lanzhou, China; ³ Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri; ⁴ Department of Electrical and System Engineering, Washington University in St. Louis, St. Louis, Missouri; and ⁵ Alvin J. Siteman Cancer Center, Washington University School of Medicine, St. Louis, Missouri

Correspondence: For correspondence or reprints contact: Yuan-Chuan Tai, Washington University School of Medicine, Campus Box 8225, 510 S. Kingshighway Blvd., St. Louis, MO 63110. E-mail: taiy{at}wustl.edu

A full-ring PET insert device should be able to enhance the image resolution of existing small-animal PET scanners. Methods: The device consists of 18 high-resolution PET detectors in a cylindric enclosure. Each detector contains a cerium-doped lutetium oxyorthosilicate array (12 x 12 crystals, 0.72 x 1.51 x 3.75 mm each) coupled to a position-sensitive photomultiplier tube via an optical fiber bundle made of 8 x 16 square multiclad fibers. Signals from the insert detectors are connected to the scanner through the electronics of the disabled first ring of detectors, which permits coincidence detection between the 2 systems. Energy resolution of a detector was measured using a ⁶⁸Ge point source, and a calibrated ⁶⁸Ge point source stepped across the axial field of view (FOV) provided the sensitivity profile of the system. A ²²Na point source imaged at different offsets from the center characterized the in-plane resolution of the insert system. Imaging was then performed with a Derenzo phantom filled with 19.5 MBq of ¹⁸F-fluoride and imaged for 2 h; a 24.3-g mouse injected with 129.5 MBq of ¹⁸F-fluoride and imaged in 5 bed positions at 3.5 h after injection; and a 22.8-g mouse injected with 14.3 MBq of ¹⁸F-FDG and imaged for 2 h with electrocardiogram gating. Results: The energy resolution of a typical detector module at 511 keV is 19.0% ± 3.1%. The peak sensitivity of the system is approximately 2.67%. The image resolution of the system ranges from 1.0- to 1.8-mm full width at half maximum near the center of the FOV, depending on the type of coincidence events used for image reconstruction. Derenzo phantom and mouse bone images showed significant improvement in transaxial image resolution using the insert device. Mouse heart images demonstrated the gated imaging capability of the device. Conclusion: We have built a prototype full-ring insert device for a small-animal PET scanner to provide higher-resolution PET images within a reduced imaging FOV. Development of additional correction techniques are needed to achieve quantitative imaging with such an insert.

Key Words: small-animal PET • high-resolution PET • PET insert • animal imaging

COPYRIGHT © 2008 by the Society of Nuclear Medicine, Inc.

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