Silicon photomultiplier performance tests in magnetic resonance pulsed fields

We are investigating the performance of silicon photomultipliers (SiPM) in a magnetic resonance imaging (MRI) environment with a view to exploiting the potential advantages in a combined positron emission tomography / magnetic resonance imaging (PET/MR) system. SiPMs are attractive for PET because they are compact, provide high gain at low bias voltage, and fast response times. Importantly for combined PET/MR applications, they offer performance comparable to that of the photomultiplier tube (PMT) and are insensitive to magnetic fields. To study the effect of MR static magnetic, pulsed gradient and radio-frequency fields on SiPM performance, we have acquired data whilst switching magnetic fields with the SiPM positioned in the MR system. The wide 'dynamic range' of SiPMs facilitates their use in both low light level and PET applications; we have acquired 'single photoelectron' and 22 Na energy spectra to demonstrate SiPM performance for this application. As expected, no degradation in inherent SiPM performance in an MR environment is observed.