Optical transmission of analog SiPM signals for ToF PET/MRI

PET/MRI systems require specialized PET detectors that can function inside of an MRI bore without interfering with MRI functionality. Ideally such a detector would be physically compact, low power, immune to interference from the MRI, and with minimal interference to the MRI, while preserving all PET timing, energy, and position information. Electro-optically coupled PET detectors, where the detector signal is transmitted out of the MRI bore optically, have been proposed to construct compact, low power PET detectors with minimal interference to and from the MRI. This work demonstrates that an analog electro-optically coupled PET detector can achieve excellent, ToF-capable, timing resolution. Timing resolution measurements were made with SiPMs coupled electrically, electro-optically with a pre-amp, and electro-optically without a pre-amp. The best FWHM coincident timing resolution achieved with 3mm × 3mm × 5mm LYSO crystals was 143ps +/- 3ps in electrical mode, 149ps +/- 4ps in electro-optical with preamp mode, and 181 +/- 3ps in electro-optical without preamp mode. With 3mm × 3mm × 20mm LYSO crystals the best timing achieved was 220 +/- 3ps in electrical mode, 231 +/- 2ps in electro-optical with preamp mode, and 253 +/- 2ps in electro-optical without preamp mode. This work shows that SiPM timing information can be preserved after analog optical transmission. This readout strategy could drastically simplify the design of high performance ToF PET/MRI systems.