Novel Electro-Optically Coupled MR-Compatible Pet Detectors

A new magnetic resonance(MR) compatible PET detector design is being developed that uses electro-optical coupling to bring the amplitude and arrival time information of high speed scintillation pulses out of an MR system. The electro-optical coupling consists of a magnetically insensitive photodetector connected to a non-magnetic vertical cavity surface emitting laser (VCSEL) diode. This scheme essentially acts as an optical wire. When compared to signal transmission over standard co-axial cables, electro-optical coupling will have little influence on a MR system because the optical fibers are not conductive. A single $3 \text{mm}\times-3\text{mm}\times20$ mm LYSO crystal coupled to a SENSL SPMArray 3035G 16 was placed in coincidence with a $4\text{mm}\times 4\text{mm}\times4$ mm LSO crystal coupled to a R9779-20 Hamamatsu PMT with and without non-magnetic VCSEL laser coupling. No change was measured in energy resolution of $15.6 +/- 0.4\%$ with electro-optical coupling versus coax-coupling energy resolution $15.5 +/- 0.4\%$. Also, no change in coincidence time resolution was measured between electro-optical coupling with $1.30 +/- 0.01$ ns FWHM versus coax at $1.32 +/- 0.02$ ns FWHM. High speed analog modulation using the VCSEL laser was successful and paves the way for a MR compatible PET block detector that has a significantly reduced electronic footprint than a standard MR compatible PET detector. This may provide the way to create a large axial FOV whole body clinical PET system that will have very little influence on a whole body clinical MR system performance.