TOF-PET Image Reconstruction With Multiple Timing Kernels Applied on Cherenkov Radiation in BGO

Efthimiou, Nikos; Kratochwil, N.; Gundacker, S.; Polesel, Andrea; Salomoni, Matteo; Auffray, E.; Pizzichemi, Marco

doi:10.1109/trpms.2020.3048642

Cited by 27 publications

(18 citation statements)

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“…To overcome the tradeoff between a "clean" signal (high threshold) and high statistics (low threshold), a weighted reconstruction could be an option where events with high number of triggered SPADs are given more priority or serve as a seed in the reconstruction process. A similar concept with a weighting based on different timing kernels for BGO was recently demonstrated (Efhimiou et al 2020). Overall, such a detector design is a completely new way of thinking (Efthimiou 2020), focusing mostly on cost and sensitivity, while energy resolution and scatter correction in the reconstruction are the weak points.…”

Section: Energy Resolutionmentioning

confidence: 99%

A roadmap for sole Cherenkov radiators with SiPMs in TOF-PET

2021

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Time of flight positron emission tomography can strongly benefit from a very accurate time estimator given by Cherenkov radiation, which is produced upon a 511 keV positron-electron annihilation gamma interaction in heavy inorganic scintillators. While time resolution in the order of 30 ps full width at half maximum (FWHM) has been reported using MCP-PMTs and black painted Cherenkov radiators, such solutions have several disadvantages, like high cost and low detection efficiency of nowadays available MCP-PMTs. On the other hand, silicon photomultipliers (SiPMs) are not limited by those obstacles and provide high photon detection efficiency with a decent time response. Timing performance of PbF 2 crystals of various lengths and surface conditions coupled to SiPMs was evaluated against a reference detector with an optimized test setup using high-frequency readout and novel time walk correction, with special attention on the intrinsic limits for one detected Cherenkov photon only. The average number of detected Cherenkov photons largely depends on the crystal surface state, resulting in a tradeoff between low photon time spread, thus good timing performance, and sensitivity. An intrinsic Cherenkov photon yield of 16.5 ± 3.3 was calculated for 2 × 2 × 3 mm 3 sized PbF 2 crystals upon 511 keV γ-deposition. After time walk correction based on the slew rate of the signal, assuming two identical detector arms in coincidence, and using all events, a time resolution of 215 ps FWHM (142 ps FWHM) was obtained for 2 × 2 × 20 mm 3 (2 × 2 × 3 mm 3 ) sized PbF 2 crystals, compared to 261 ps (190 ps) without correction. Selecting on one detected photon only, a single photon coincidence time resolution of 113 ps FWHM for black painted and 166 ps for Teflon wrapped crystals was measured for 3 mm length, compared to 145 ps (black) and 263 ps (Teflon) for 20 mm length.

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Section: Energy Resolutionmentioning

confidence: 99%

A roadmap for sole Cherenkov radiators with SiPMs in TOF-PET

2021

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“…However, since the rise time information allows classification of events, a gain in SNR is expected when each category of the events is allocated to its proper TOF kernel; thus, events having a better time resolution can provide higher TOF kernel resolution along the LOR and thus better reconstructed image SNR, while events with worse time resolution are used in addition to maintain the high sensitivity of BGO [20]. The work presented in [39] reports a simulation toolkit that introduces multiple timing spreads on the coincident events of a full cylindrical BGO-Cherenkov PET model and an image reconstruction procedure that incorporates the multi-kernel idea. The results demonstrate a better contrast-to-noise ratio for the multi-kernel BGO model.…”

Section: Discussionmentioning

confidence: 99%

“…Acquired data will be transferred to a PC for the application of the correction methods which will be followed by image reconstruction. The inclusion of several TOF kernels in reconstruction was already demonstrated in [39], so we will follow a similar approach. However, this is out of the scope of this article and will be discussed in detail in a future work.…”

Section: Discussionmentioning

confidence: 99%

Cherenkov Radiation–Based Coincidence Time Resolution Measurements in BGO Scintillators

et al. 2022

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Bismuth germanate oxide (BGO) scintillators can be re-introduced in time-of-flight positron emission tomography (TOF-PET) by exploiting the Cherenkov luminescence emitted as a result from 511 keV interactions. Accessing the timing information from the relatively few emitted Cherenkov photons is now possible due to the recent improvements in enhanced near-ultraviolet high-density (NUV-HD) silicon photomultiplier (SiPM) technology, fast and low noise readout electronics, and the development of efficient data post-processing methods. In this work, we aim to develop a scalable detector element able to achieve excellent coincidence time resolution (CTR) required for TOF-PET using BGO scintillator elements of various lengths. The proposed detector element is optically coupled to 3.14 × 3.14 mm2 NUV-sensitive SiPMs mounted on a custom design circuit board. In particular, we have evaluated the CTR performance of BGO crystal elements of dimensions 3 × 3 × 3 mm3, 3 × 3 × 5 mm3, 3 × 3 × 10 mm3, and 3 × 3 × 15 mm3, with chemically etched surfaces and wrapped in Teflon tape. To achieve excellent CTR performance, we apply state-of-the-art post-processing methods during data analysis. Best values of 156 ± 6 ps, 188 ± 5 ps, 228 ± 8 ps, and 297 ± 8 ps CTR FWHM have been achieved for the 3, 5, 10, and 15 mm length BGO crystals, respectively. These values improve to 105 ± 6 ps, 127 ± 8 ps, 133 ± 4 ps, and 189 ± 8 ps CTR FWHM, when only considering the Cherenkov component of the timing signal, which is extracted by considering the events with the fastest rise time (20% of the total data). The accurate classification of the events based on their rise time is possible; thanks to the implementation of a dual threshold approach that sets the lower threshold below one light photon equivalent level and the upper one above the signal amplitude of a single photon avalanche diode (SPAD).

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“…The coincidence window was set to 4 ns and the GATE parameter minSectorDifference to 88 [32]. In previous work on TOF PET reconstruction applied on Cherenkov radiation in BGO [28], an energy resolution of 19% was considered, whereas, for the heterostructured scintillators, worse resolution can be expected due to the layered structure. However, here, to isolate the effects of CTR on the reconstruction of TOF PET image reconstruction, the same energy resolution 20% and an energy window of 400 − 650 keV were used in all models.…”

Section: B Monte Carlo Simulationsmentioning

confidence: 99%

“…The properties of EJ232 are very similar to BC422 (Saint-Gobain), which was used by [20]. In the image reconstruction, we exploited the fraction of events with a faster CTR by applying different timing kernels [28]. We compare the performance of a heterostructure-based scanner to one with bulk BGO detectors in terms of count rates and the quality of the reconstructed images in terms of contrast recovery coefficient (CRC) and contrast to noise ratio (CNR) using the NEMA IQ phantom.…”

mentioning

confidence: 99%

Image Reconstruction Analysis for Positron Emission Tomography With Heterostructured Scintillators

Mohr

Efthimiou

Pagano

et al. 2023

IEEE Trans. Radiat. Plasma Med. Sci.

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The concept of structure engineering has been proposed for exploring the next generation of radiation detectors with improved performance. A TOF-PET geometry with heterostructured scintillators with a pixel size of 3.0 × 3.1 × 15 mm 3 was simulated using Monte Carlo. The heterostructures consisted of alternating layers of BGO as a dense material with high stopping power and plastic (EJ232) as a fast light emitter. The detector time resolution was calculated as a function of the deposited and shared energy in both materials on an event-by-event basis. While sensitivity was reduced to 32% for 100 µm thick plastic layers and 52% for 50 µm, the CTR distribution improved to 204 ± 49 ps and 220 ± 41 ps respectively, compared to 276 ps that we considered for bulk BGO. The complex distribution of timing resolutions was accounted for in the reconstruction. We divided the events into three groups based on their CTR and modeled them with different Gaussian TOF kernels. On a NEMA IQ phantom, the heterostructures had better contrast recovery in early iterations. On the other hand, BGO achieved a better contrast to noise ratio (CNR) after the 15th iteration due to the higher sensitivity. The developed simulation and reconstruction methods constitute new tools for evaluating different detector designs with complex time responses.

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TOF-PET Image Reconstruction With Multiple Timing Kernels Applied on Cherenkov Radiation in BGO

Cited by 27 publications

References 50 publications

A roadmap for sole Cherenkov radiators with SiPMs in TOF-PET

A roadmap for sole Cherenkov radiators with SiPMs in TOF-PET

Cherenkov Radiation–Based Coincidence Time Resolution Measurements in BGO Scintillators

Image Reconstruction Analysis for Positron Emission Tomography With Heterostructured Scintillators

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