A prototype detector module for combined PET/CT or combined photon counting/standard CT based on SiPM technology

A method extending the functionality of silicon photomultipliers (SiPMs) has been developed. It enables the use of SiPMs for quantifying high radiation fluxes in current mode as well as in pulse mode measurements for counting and characterizing individual gamma-ray or X-ray photons when coupled to scintillators. This opens new possibilities for multimodal medical imaging by providing the means for producing common radiation sensors for PET, standard CT and photon counting CT. Currently, two separate detector systems are required for combined PET/CT. Similarly, standard current integrating CT and the novel concept of photon counting CT currently also requires separate detector systems. We here present a novel detector design featuring dual-mode readout of SiPM-based radiation sensors that enables imaging systems where conventional CT imaging is combined with PET, as well as in CT systems where both conventional integrating (high-flux) and photon counting (low-dose) operation can be selected. Such dual-mode SiPMs coupled to scintillators in medical imaging can be used to detect and characterize single primary X-ray or gamma-ray photons up to fluxes of millions of photons per mm² per second in pulse mode. Current mode operation allows the dynamic range to be extended to the much higher rates found in standard CT imagers and beyond. A prototype detector is being developed and studied from the point of view of the energy and timing resolution required for the photon-counting application as well as the flux-to-current characteristics, essential for the current mode.