Coincidence time resolution of 30 ps FWHM using a pair of Cherenkov-radiator-integrated MCP-PMTs

Radiation detectors dedicated to time-of-flight positron emission tomography (PET) have been developed, and coincidence time resolution (CTR) of sub-100 ps full width at half maximum (FWHM) has been achieved by carefully optimizing scintillators and photodetectors. Achieving a CTR of 30 ps FWHM by using a pair of annihilation γ-rays would allow us to directly localize the annihilation point within an accuracy of 4.5 mm. Such direct localization can potentially eliminate the requirement of image reconstruction processes in clinical PET systems, which would have a huge impact on clinical protocols and molecular imaging. To obtain such a high CTR, researchers have investigated the use of prompt emissions such as Cherenkov radiation and hot-intra band luminescence. Although it is still challenging to achieve a CTR of 30 ps FWHM even with a Cherenkov-based detector, the experimentally measured CTR is approaching the goal. In this work, we developed a Cherenkov-radiator-integrated micro-channel plate photomultiplier tube (CRI-MCP-PMT), where there are no optical boundaries between the radiator and photocathode, and its timing performance was investigated. By removing the optical boundaries, reflections are eliminated and transmission to the photocathode is improved, resulting in high timing capability. As a result, a CTR of 30.1 ± 2.4 ps FWHM, which is equivalent to a position resolution of 4.5 ± 0.3 mm along a line of response (LOR), was obtained by using a pair of CRI-MCP-PMTs.