Speaker
Description
Image quality of positron emission tomography (PET) can be enhanced using time-of-flight (TOF) information between a pair of PET detectors. Coincidence time resolution (CTR) of commercially available TOF-PET scanners is as high as ~200 ps full width at half maximum (FWHM), showing improved PET image quality compared with non-TOF PET images. Theoretically, CTR can improve the signal to noise ratio of PET images as the inverse square root of CTR, indicating that further improved CTR can enhance PET image quality. Moreover, when CTR reaches 30 ps FWHM, the spatial precision calculated from CTR becomes 4.5 mm, which is comparable to the spatial resolution of earlier-generation clinical PET scanners. This implies that PET scanners may no longer need to be cylindrical systems that surround a patient’s body and require image reconstruction processes, because such an ultrafast CTR can directly provide spatial information on the electron–positron annihilation position within the patient, potentially making PET systems more compact and flexible. However, achieving a CTR of 30 ps FWHM remains challenging even with the current state of the art scintillators and photodetectors. Detecting Cherenkov photons instead of scintillation photons has recently attracted attention as a possible approach to achieving the theoretical CTR limitation because Cherenkov photons are emitted on the order of picoseconds and can be several orders of magnitude faster than scintillation photons. On the other hand, the number of Cherenkov photons emitted is significantly less than that of scintillation photons. Therefore, effectively collecting Cherenkov photons while maintaining their excellent timing property is challenging. To address this issue, Cherenkov radiator-integrated microchannel plate photomultiplier tube (CR-IMP, formerly CRI-MCP-PMT) was developed and a CTR of ~30 ps FWHM was experimentally demonstrated. Furthermore, the use of a pair of CR-IMPs enabled the acquisition of two-dimensional cross-sectional images of a phantom filled with positron emitting radionuclide using only TOF information, without a conventional image reconstruction process. However, the demonstration employed two single channel detectors, which are too bulky to construct a practical system using multiple detectors. Hence, the development of position-sensitive multi-anode (MA) MCP-PMTs is the next step towards realizing the reconstruction-free imaging concept. In this study, we present the first fabricated 4×4 multi-anode MCP-PMTs whose window faceplate is replaced with bismuth germanate (BGO), which serves as a hybrid Cherenkov/scintillation material that enables simultaneous measurement of ultrafast CTR and energy information, which require clinical systems. This study focuses not only on the integration of BGO into an MA-MCP-PMT structure but also on the implementation of a super bialkali photocathode for enhancing probability of Cherenkov photon detection with high quantum efficiency (QE). At this stage, the timing performance of the detector remains unoptimized. The developed detector has an active area of 23 × 23 mm2 with the channel readout pitch of 5.75 mm. A maximum QE is 27.6% at 340 nm is achieved owing to the implementation of the super bialkali photocathode. In addition to the QE curve, in this presentation, we will show preliminary evaluations of the MA-BGO-IMP, such as gain, dark count rate, single photon response, etc.
| Track | FTMI |
|---|---|
| Presentation type | Oral |