Ultrafast timing enables reconstruction-free positron emission imaging

Kwon, Sun Il; Ota, Ryosuke; Berg, Eric; Hashimoto, Fumio; Nakajima, K.; Ogawa, Izumi; Tamagawa, Y.; Omura, T.; Hasegawa, Tomoyuki; Cherry, Simon R.

doi:10.1038/s41566-021-00871-2

Cited by 72 publications

(37 citation statements)

References 22 publications

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“…Using promptly emitted Cerenkov photons to achieve superior timing resolution in time-of-flight positron emission tomography (TOF PET) has been the core of several recent studies [9][10][11][12][13][14][15][16]. These studies underscored the challenges associated with time triggering based on the very few Cerenkov photons produced per photoelectric interaction and indicated the need for a more detailed understanding of the light transport in the crystal and collection by the photodetector.…”

Section: Introductionmentioning

confidence: 99%

The Accuracy of Cerenkov Photons Simulation in Geant4/Gate Depends on the Parameterization of Primary Electron Propagation

et al. 2022

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Energetic electrons traveling in a dispersive medium can produce Cerenkov radiation. Cerenkov photons’ prompt emission, combined with their predominantly forward emission direction with respect to the parent electron, makes them extremely promising to improve radiation detector timing resolution. Triggering gamma detections based on Cerenkov photons to achieve superior timing resolution is challenging due to the low number of photons produced per interaction. Monte Carlo simulations are fundamental to understanding their behavior and optimizing their pathway to detection. Therefore, accurately modeling the electron propagation and Cerenkov photons emission is crucial for reliable simulation results. In this work, we investigated the physics characteristics of the primary electrons (velocity, energy) and those of all emitted Cerenkov photons (spatial and timing distributions) generated by 511 keV photoelectric interactions in a bismuth germanate crystal using simulations with Geant4/GATE. Geant4 uses a stepwise particle tracking approach, and users can limit the electron velocity change per step. Without limiting it (default Geant4 settings), an electron mean step length of ∼250 μm was obtained, providing only macroscopic modeling of electron transport, with all Cerenkov photons emitted in the forward direction with respect to the incident gamma direction. Limiting the electron velocity change per step reduced the electron mean step length (∼0.200 μm), leading to a microscopic approach to its transport which more accurately modeled the electron physical properties in BGO at 511 keV. The electron and Cerenkov photons rapidly lost directionality, affecting Cerenkov photons’ transport and, ultimately, their detection.Results suggested that a deep understanding of low energy physics is crucial to perform accurate optical Monte Carlo simulations and ultimately use them in TOF PET detectors.

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Section: Introductionmentioning

confidence: 99%

The Accuracy of Cerenkov Photons Simulation in Geant4/Gate Depends on the Parameterization of Primary Electron Propagation

et al. 2022

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“…However, as discussed in the previous sections, quantitative PET imaging without calculating line integrals to include the effect of photon attenuation, or without using iterative techniques to e.g., estimate the contribution scattered coincidenes or to find the maximum likelihood or maximum a posteriori estimator, is not feasible. As demonstrated in the proof-of-concept by Kwon et al (11), in the absence of scattered coincidences, direct PET imaging is in principle possible . However, the question remains whether simple direct (reconstruction-free) methods will yield "optimal" image quality concerning image resolution and noise compared to more advanced (iterative) reconstruction techniques in realistic PET systems with "perfect" TOF resolution.…”

Section: Discussionmentioning

confidence: 96%

“…In a remarkable work, Kwon et al (11) recently showed that it is possible to build a PET imaging system based on the detection of Cherenkov photons in two collimated detectors that has a coincidence TOF resolution of 32 ps meaning that σ ≈ σ ⊥ . In their article, the authors argue that by having detectors with such excellent coincidence TOF resolution a PET "image can be directly obtained without any reconstruction step" (direct positron emission imaging or reconstructionfree PET).…”

Section: Introductionmentioning

confidence: 99%

Reconstruction-free positron emission imaging: Fact or fiction?

Schramm

2022

Front. Nucl. Med.

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“…PbF 2 was first experimentally studied by Korpar et al 2011 [13], where a 95 ps FWHM coincidence time resolution (CTR) was measured for 15 mm long crystals coupled to a microchannel plate photomultiplier (MCP-PMT) as the light sensor. Recently, a Cherenkov-radiator-integrated micro-channel plate photomultiplier tube (CRI-MCP-PMT), where there are no optical boundaries between the radiator and photocathode, achieved an outstanding CTR of around 30 ps FWHM [14] and direct (reconstruction-free) positron emission imaging was demonstrated using these fast detectors [15]. However, to achieve such resolution, strong cuts had to be made in timing pick-off threshold and pulse area, meaning only a small fraction of events was used, and the authors acknowledge that these detectors do not satisfy the detection efficiency requirement of clinical PET detectors.…”

Section: B Time-of-flightmentioning

confidence: 99%

Exploring the Potential of a Cherenkov TOF PET Scanner: A Simulation Study

Razdevsek

Pestotnik²,

Križan

et al. 2023

IEEE Trans. Radiat. Plasma Med. Sci.

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The detection of annihilation photons in PET is based on scintillation light detection, but an interesting alternative is detection based on Cherenkov photons. Dense Cherenkov radiators provide an opportunity for high gamma detection efficiency -due to their high stopping power and photofraction -and excellent coincidence time resolution (CTR). However, because only a few tens of Cherenkov photons follow a gamma interaction in the radiator, the detection efficiency and the energy resolution of a pure Cherenkov detector are an issue. This work explores gamma detection efficiency and CTR of PbF2 based detectors with different surface treatments and photo-detectors covering one, two, or all crystal faces. Following the detector simulation analysis, we investigate the potential performance of a full-size Cherenkov PET scanner and quantitatively compare image quality with a commercial clinical PET scanner. We demonstrate that even though pure Cherenkov scanners have basically no energy resolution, the scatter fraction of around 50% is not prohibitively large, and images comparable to the stateof-the-art clinical PET scanner can be achieved due to improved efficiency and CTR attainable with PbF2.

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Ultrafast timing enables reconstruction-free positron emission imaging

Cited by 72 publications

References 22 publications

The Accuracy of Cerenkov Photons Simulation in Geant4/Gate Depends on the Parameterization of Primary Electron Propagation

The Accuracy of Cerenkov Photons Simulation in Geant4/Gate Depends on the Parameterization of Primary Electron Propagation

Reconstruction-free positron emission imaging: Fact or fiction?

Exploring the Potential of a Cherenkov TOF PET Scanner: A Simulation Study

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