Precise analysis of the timing performance of Cherenkov-radiator-integrated MCP-PMTs: analytical deconvolution of MCP direct interactions

Ota, Ryosuke; Nakajima, K.; Ogawa, Izumi; Tamagawa, Y.; Shimoi, Hideki; Suyama, Motohiro; Hasegawa, Tomoyuki

doi:10.1088/1361-6560/ab8c8f

Cited by 6 publications

(8 citation statements)

References 28 publications

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“…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). Nevertheless, their outstanding experimental result shows that the physics of positron annihilation do not prohibit a CRT of 30 ps FWHM.…”

Section: Towards 10 Ps Pet?mentioning

confidence: 99%

Physics and technology of time-of-flight PET detectors

Schaart

2021

Phys. Med. Biol.

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The imaging performance of clinical positron emission tomography (PET) systems has evolved impressively during the last ∼15 years. A main driver of these improvements has been the introduction of time-of-flight (TOF) detectors with high spatial resolution and detection efficiency, initially based on photomultiplier tubes, later silicon photomultipliers. This review aims to offer insight into the challenges encountered, solutions developed, and lessons learned during this period. Detectors based on fast, bright, inorganic scintillators form the scope of this work, as these are used in essentially all clinical TOF-PET systems today. The improvement of the coincidence resolving time (CRT) requires the optimization of the entire detection chain and a sound understanding of the physics involved facilitates this effort greatly. Therefore, the theory of scintillation detector timing is reviewed first. Once the fundamentals have been set forth, the principal detector components are discussed: the scintillator and the photosensor. The parameters that influence the CRT are examined and the history, state-of-the-art, and ongoing developments are reviewed. Finally, the interplay between these components and the optimization of the overall detector design are considered. Based on the knowledge gained to date, it appears feasible to improve the CRT from the values of 200-400 ps achieved by current state-of-the-art TOF-PET systems to about 100 ps or less, even though this may require the implementation of advanced methods such as time resolution recovery. At the same time, it appears unlikely that a system-level CRT in the order of ∼10 ps can be reached with conventional scintillation detectors. Such a CRT could eliminate the need for conventional tomographic image reconstruction and a search for new approaches to timestamp annihilation photons with ultra-high precision is therefore warranted. While the focus of this review is on timing performance, it attempts to approach the topic from a clinically driven perspective, i.e. bearing in mind that the ultimate goal is to optimize the value of PET in research and (personalized) medicine. Selected abbreviations and symbols BSR Backside readout C d Diode capacitance CFD Constant-fraction discriminator CRLB Cramér-Rao lower bound CRT Coincidence resolving time C q Parallel capacitance of quench resistor DCR Dark count rate DOI Depth of interaction dSiPM Digital silicon photomultiplier DSR Dual-sided readout

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Section: Towards 10 Ps Pet?mentioning

confidence: 99%

Physics and technology of time-of-flight PET detectors

Schaart

2021

Phys. Med. Biol.

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“…The standard window face plate of the LFMCP-based MCP-PMT (LFMCP-PMT) was replaced with a lead compound glass, which acted as a Cherenkov radiator, using an atomic layer deposition (ALD) technique as in our previous works (Ota et al 2019a(Ota et al , 2020a. Owing to the integration of the Cherenkov radiator, the Cherenkov photons produced in the radiator can be efficiently detected by the photocathode.…”

Section: Lead-free Mcp-based Mcp-pmtmentioning

confidence: 99%

“…In this study, we investigated the timing performance of the LFMCP-PMT and the influence of parameters such as DV 1 and DV 3 for the divider circuit. The timing performance was compared to that of the LGMCP-PMT obtained in our previous work (Ota et al 2020a). In addition, the reduction of direct interaction of the LFMCP to gamma rays is assessed.…”

Section: Experiments and Analysismentioning

confidence: 99%

“…After the event selection, the analysis was performed in the same manner as in the previous works of (Ota et al 2019a(Ota et al , 2019b(Ota et al , 2020a. Spline curves were obtained from the digitized waveforms using the TSpline3 class method implemented in ROOT (Brun and Rademakers 1997) in which the detection timings of both LFMCP-PMTs at arbitrary threshold levels were recorded.…”

Section: Experiments and Analysismentioning

confidence: 99%

“…In our previous work, results show that gamma rays frequently and directly interact with the MCP structure wherein the photoelectron or recoil electron is directly multiplied without generating detectable optical photons, causing undesirable side peaks in the coincidence timing spectrum due to the relatively high effective atomic number of the lead glass used for the MCP structure (Ota et al 2019b). Although these MCP direct interactions show good timing performance (Barnyakov et al 2017, Ota et al 2020a, they should be eliminated from the coincidence timing spectrum to obtain the best timing performance for direct imaging, as these side peaks would otherwise generate artifacts (events mispositioned by several cm) in the PET images. The removal of lead compounds from the MCP-PMT structure also is consistent with environmental directives (The European Parliament and the Council of the European Union 2003).…”

Section: Introductionmentioning

confidence: 99%

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Lead-free MCP to improve coincidence time resolution and reduce MCP direct interactions

et al. 2021

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Achieving direct imaging of the annihilation position of a positron on an event-by-event basis using an ultrafast detector would have a great impact on the field of nuclear medicine. Cherenkov emission is the most attractive physical phenomenon for realizing such an ultrafast timing performance. Moreover, a microchannel-plate photomultiplier tube (MCP-PMT) is one of the most promising photodetectors for fully exploiting the fast timing properties of Cherenkov emission owing to its excellent single photon time resolution of 25 ps full width at half maximum (FWHM). However, as the MCP structure generally contains a lead compound, the gamma rays frequently and directly interact with the MCP, resulting in the degradation of its timing performance and generation of undesirable side peaks in its coincidence timing histogram. To overcome this problem, we have developed a new MCP-PMT based on an MCP consisting of borosilicate glass, thus drastically reducing the probability of the photoelectric effect occurring in the MCP. To evaluate its insensitivity to gamma rays and its timing performance, a coincidence experiment was performed and showed that the probability of direct interactions was reduced by a factor of 3.4. Moreover, a coincidence time resolution of 35.4 ± 0.4 ps FWHM, which is equivalent to a position resolution of 5.31 mm, was obtained without any pulse height/area cut, improving to 28.7 ± 3.0 ps when selecting on the highest amplitude events by careful optimization of the voltage divider circuit of the new MCP-PMT. The timing performance of this new MCP-PMT presents an important step toward making direct imaging possible.

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