Performance test of an LSO-APD detector in a 7-T MRI scanner for simultaneous PET/MRI

PET combined with CT has proven to be a valuable multimodality imaging device revealing both functional and anatomic information. Although PET/CT has become completely integrated into routine clinical application and also has been used in small-animal imaging, CT provides only limited soft-tissue contrast and, in preclinical studies, exposes the animal to a relatively high radiation dose. Unlike CT, MRI provides good soft-tissue contrast even without application of contrast agents and, furthermore, does not require ionizing radiation. Methods: This project focused on combining a high-resolution PET scanner with a 7-T MRI system for animal research. Because classic PET detectors based on photomultiplier tubes cannot be used in high magnetic fields, we used a detector technology based on 10 x 10 lutetium oxyorthosilicate crystal arrays and 3 x 3 avalanche photodiode arrays. A ring of such PET detectors will ultimately be used as an insert for the 119-mm-diameter MRI bore. Results: Initial measurements with 1 PET detector module in the 7-T field during application of MRI sequences were encouraging. Position profiles from the PET detectors and a first MR image of a mouse could be acquired simultaneously. Conclusion: Further work will concentrate on the construction of a full PET detector ring with compact, integrated electronics.