MR compatibility aspects of a silicon photomultiplier-based PET/RF insert with integrated digitisation

• Published in: Physics in medicine & biology 2014-09, Vol.59 (17), p.5119-5139
• Main Authors: Weissler, Bjoern, Gebhardt, Pierre, Lerche, Christoph W., Wehner, Jakob, Solf, Torsten, Goldschmidt, Benjamin, Mackewn, Jane E., Marsden, Paul K., Kiessling, Fabian, Perkuhn, Michael, Heberling, Dirk, Schulz, Volkmar
• Format: Article
• Language: English
• Subjects: animal imaging; Animals; instrumentation; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; molecular imaging; MRI; Multimodal Imaging - instrumentation; Multimodal Imaging - methods; multimodality imaging; PET; Positron-Emission Tomography - instrumentation; Positron-Emission Tomography - methods; Rats; Signal-To-Noise Ratio; Silicon - chemistry; silicon photo multiplier
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/59/17/5119

The combination of Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) into a single device is being considered a promising tool for molecular imaging as it combines the high sensitivity of PET with the functional and anatomical images of MRI. For highest performance, a scalable, MR compatible detector architecture with a small form factor is needed, targeting at excellent PET signal-to-noise ratios and time-of-flight information. Therefore it is desirable to use silicon photo multipliers and to digitize their signals directly in the detector modules inside the MRI bore. A preclinical PET/RF insert for clinical MRI scanner was built to demonstrate a new architecture and to study the interactions between the two modalities. The disturbance of the MRI's static magnetic field stays below 2 ppm peak-to-peak within a diameter of 56 mm (90 mm using standard automatic volume shimming). MRI SNR is decreased by 14%, RF artefacts (dotted lines) are only visible in sequences with very low SNR. Ghosting artefacts are visible to the eye in about 26% of the EPI images, severe ghosting only in 7.6%. Eddy-current related heating effects during long EPI sequences are noticeable but with low influence of 2% on the coincidences count rate. The time resolution of 2.5 ns, the energy resolution of 29.7% and the volumetric spatial resolution of 1.8 mm3 in the PET isocentre stay unaffected during MRI operation. Phantom studies show no signs of other artefacts or distortion in both modalities. A living rat was simultaneously imaged after the injection with 18F-Fluorodeoxyglucose (FDG) proving the in vivo capabilities of the system.