PET/MR Images Acquired with a Compact MR-compatible PET Detector in a 7-T Magnet

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Abstract
To prospectively use compact avalanche photodiodes instead of photomultiplier tubes to integrate a positron emission tomographic (PET) detector and a 7-T magnetic resonance (MR) imager. All animal experiments were performed in accordance with the University of Tübingen guidelines and the German law for the protection of animals. A compact lutetium oxyorthosilicate-avalanche photodiode PET detector was built and optimized to operate within a 7-T MR imager. The detector performance was investigated both outside and inside the magnet, and MR image quality was evaluated with and without the PET detector. Two PET detectors were set up opposite each other and operated in coincidence to acquire PET images in the step-and-shoot mode in a mouse head specimen after injection of fluorine 18 fluorodeoxyglucose. The performance of the PET detector when operated inside the magnet during MR image acquisition showed little degradation in energy resolution (increase from 14.6% to 15.9%). The PET detector did not influence MR imaging. The fused PET and MR images showed an anatomic match and no degradation of image quality. Simultaneous PET and MR imaging with a 7-T system was deemed feasible.