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

Abstract

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.

Prospects and Clinical Perspectives of Total-Body PET Imaging Using Plastic Scintillators

“…29 Current clinical time of flight (TOF)-PETs 12 achieve down to 210 ps and small laboratory type detectors reach CRT of even 30 ps equivalent to position resolution of 4.5 mm along the line of response. 99 Therefore, with the continuous improvement of the time resolution 25,100 it may become feasible in not so distant future to reconstruct positronium image directly as a density distribution of annihilation points. 29,30 Resent simulation studies 29 indicate that the PSF of positronium image equals to approximately 5 mm (radial and axial) for CRT 5 50 ps.…”

Pair production tomography imaging

“…TOF relies heavily on the time resolution of the detector, requiring a 20 ps time resolution to localize the annihilation event within an accuracy of 3 mm. The 20 ps time resolution detector is consistent with the roadmap of PET detection using prompt Cherenkov emission 19,20 or ultrafast emitting quantum-confined systems 34,35 , although both still require significant engineering development to be practical 36 . On the other hand, the SPB significantly relaxes the required time resolution due to the known excitation path.…”

“…The detector response time is simulated as a Gaussian distribution with a standard deviation equal to the time resolution of the detector. We considered two cases: time resolution of 20 ps or 300 ps, representing the upper limits of experimental Cerenkov 19,20 and state of the art commercial scintillator detectors 21 , respectively.…”

Physics and technology of time-of-flight PET detectors

“…As the photocathode is applied directly to the lead glass, h ot and ( ) p t t ot are greatly improved. Ota et al (2019) furthermore covered the lead glass top surfaces with black tape to avoid reflections and selected only the events with the highest photon count. They acknowledge that the resulting detection efficiency does not yet satisfy the requirements of a clinical PET detector (Ota et al 2020).…”