A thick semi-monolithic scintillator detector for clinical PET scanners

Zhang, Chunhui; Wang, Xiaohui; Sun, Mingguang; Kuang, Zhonghua; Zhang, Xianming; Ren, Na; Wu, San; Sang, Ziru; Sun, Tao; Hu, Zhanli; Yang, Yongfeng; Liu, Zheng

doi:10.1088/1361-6560/abe761

Cited by 15 publications

(14 citation statements)

References 48 publications

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“…51 Most recently, Zhang et al presented an adaption of their detector for clinical applications increasing the height to 20 mm and thickness to 1.37 mm while still keeping a lightguide to resolve the slabs along the segmented direction. 52 The detector utilized a silicon photomultiplier (SiPM) array of 3 mm channel pitch and was read out by the TOFPET2 ASIC (PETsys electronics). A SR of 2.43 mm FWHM along the monolithic direction and 4.77 mm FWHM for DOI was achieved for onesided readout.…”

Section: Introductionmentioning

confidence: 99%

A semi‐monolithic detector providing intrinsic DOI‐encoding and sub‐200 ps CRT TOF‐capabilities for clinical PET applications

et al. 2022

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Background Current clinical positron emission tomography (PET) systems utilize detectors where the scintillator typically contains single elements of 3–6‐mm width and about 20‐mm height. While providing good time‐of‐flight performance, this design limits the spatial resolution and causes radial astigmatism as the depth‐of‐interaction (DOI) remains unknown. Purpose We propose an alternative, aiming to combine the advantages of current detectors with the DOI capabilities shown for monolithic concepts, based on semi‐monolithic scintillators (slabs). Here, the optical photons spread along one dimension enabling DOI‐encoding with a still small readout area beneficial for timing performance. Methods An array of eight monolithic LYSO slabs of dimensions 3.9 × 32 × 19 mm3 was read out by a 64‐channel photosensor containing digital SiPMs (DPC3200‐22‐44, Philips Digital Photon Counting). The position estimation in the detector's monolithic and DOI direction was based on a calibration with a fan beam collimator and the machine learning technique gradient tree boosting (GTB). Results We achieved a positioning performance in terms of mean absolute error (MAE) of 1.44 mm for the monolithic direction and 2.12 mm for DOI considering a wide energy window of 300–700 keV. The energy resolution was determined to be 11.3%, applying a positional‐dependent energy calibration. We established both an analytical and machine‐learning‐based timing calibration approach and applied them for a first‐photon trigger. The analytical timing calibration corrects for electronic and optical time skews leading to 240 ps coincidence resolving time (CRT) for a pair of slab‐detectors. The CRT was significantly improved by utilizing GTB to predict the time difference based on specific training data and applied on top of the analytical calibration. We achieved 209 ps for the wide energy window and 198 ps for a narrow selection around the photopeak (411–561 keV). To maintain the detector's sensitivity, no filters were applied to the data during processing. Conclusion Overall, the semi‐monolithic detector provides attractive performance characteristics. Especially, a good CRT can be achieved while introducing DOI capabilities to the detector, making the concept suitable for clinical PET scanners.

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Section: Introductionmentioning

confidence: 99%

A semi‐monolithic detector providing intrinsic DOI‐encoding and sub‐200 ps CRT TOF‐capabilities for clinical PET applications

et al. 2022

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“…For comparison purposes, the timing resolution between a semi-monolithic block and a reference pixel crystal with a semi-monolithic detector of nine slabs of 1.37 × 51.2 × 20 mm 3 was around 780 ps for singleended readout configuration and 718 ps for doubleended readout configuration, as shown in another recent work. 9 In these results, only the time skew was corrected.…”

Section: Discussionmentioning

confidence: 99%

“…In a recent work, a larger semi-monolithic block with dimensions of 1.37 × 51.2 × 20 mm 3 was studied using single and dual-ended readout. 9 The best results were found for the dual-ended readout case, since this configuration allowed to partially compensate the negative effects on the detector performance due to the increase in the height of the slabs.…”

Section: Introductionmentioning

confidence: 99%

“…The timing and energy resolutions were improved to 596 ps and 15.8%, respectively, with ESR treatment, but the spatial and DOI resolution worsen to 1.77 mm and 2.71 mm, respectively. In a recent work, a larger semi‐monolithic block with dimensions of 1.37 × 51.2 × 20 mm 3 was studied using single and dual‐ended readout 9 . The best results were found for the dual‐ended readout case, since this configuration allowed to partially compensate the negative effects on the detector performance due to the increase in the height of the slabs.…”

Section: Introductionmentioning

confidence: 99%

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Timing evaluation of a PET detector block based on semi‐monolithic LYSO crystals

et al. 2021

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Purpose: Detectors for positron emission tomography (PET) typically use two types of scintillation crystals, pixelated or monolithic. A variant of these types of scintillators are the so-called semi-monolithic crystals. They consist of a monolithic crystal segmented in one direction in pieces called slabs. These scintillators have the potential to successfully combine the benefits of pixelated and monolithic configurations, providing good timing and spatial resolutions as well as the capacity to decode the depth of interaction (DOI) information. In this work, the timing performance of a detector based on semi-monolithic crystals was studied in depth. The energy response was also evaluated. Methods: The semi-monolithic detector consists of 1 × 24 LYSO slabs of 25.4 × 12 × 0.95 mm 3 each. The bottom surface of the slabs is coupled to an array of 8 × 8 silicon photomultipliers (SiPMs) of 3 × 3 mm 2 active area, 50 μm cell size and 3.2 mm pitch. The 64 output signals were independently readout by the TOFPET2 ASIC. In order to achieve the best coincidence time resolution (CTR), four different time walk corrections were tested. Additional work investigated the best method of combining the timestamps belonging to the same event.Results: The resolvability of the slabs in the measured flood maps improves with the thickness of a light guide placed in between the scintillators and photosensors. The energy resolution does not change significantly with values as good as 13.7%. Regarding the CTR, values of 335.8, 363, 369.8, and 402.5 ps have been obtained for the whole detector for no light guide, 0.5, 1.0, and 1.5 mm thickness light guide cases, respectively. These values further improve to 276.1, 302.6, 305.6 and 336.2 ps, respectively, when energy-weighted averaging of timestamps is applied. Conclusions: We have shown both an excellent timing resolution and good energy resolution for a PET detector based on semi-monolithic crystals. The use of light guides of different thicknesses does not significantly affect the energy resolution of the whole detector, but the timing capabilities slightly worsen with the increasing thickness of the light guide.

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“…In recent publications [33,[41][42][43], it has been shown that (semi-)monolithic detectors are able to provide good performances. Especially the timing capabilities of (semi-)monolithic detectors have been studied under various experimental settings.…”

Section: B Timing Capabilities Of Pet Detectorsmentioning

confidence: 99%

Improving the Timing Resolution of Positron Emission Tomography Detectors using Boosted Learning -- A Residual Physics Approach

Naunheim¹,

Kuhl²,

Schug³

et al. 2023

Preprint

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Artificial intelligence is finding its way into medical imaging, usually focusing on image reconstruction or enhancing analytical reconstructed images. However, optimizations along the complete processing chain, from detecting signals to computing data, enable significant improvements. Adaptions of the data acquisition and signal processing are potentially easier to translate into clinical applications, as no patient data are involved in the training. At the same time, the robustness of the involved algorithms and their influence on the final image might be easier to demonstrate. Thus, we present an approach toward detector optimization using boosted learning by exploiting the concept of residual physics. In our work, we improve the coincidence time resolution (CTR) of positron emission tomography (PET) detectors. PET enables imaging of metabolic processes by detecting γ-photons with scintillation detectors. Current research exploits light-sharing detectors, where the scintillation light is distributed over and digitized by an array of readout channels. While these detectors demonstrate excellent performance parameters, e.g., regarding spatial resolution, extracting precise timing information for time-of-flight (TOF) becomes more challenging due to deteriorating effects called time skews. Conventional correction methods mainly rely on analytical formulations, theoretically capable of covering all time skew effects, e.g., caused by signal runtimes or physical effects. However, additional effects are involved for lightsharing detectors, so finding suitable analytical formulations can become arbitrarily complicated. The residual physicsbased strategy uses gradient tree boosting (GTB) and a

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A thick semi-monolithic scintillator detector for clinical PET scanners

Cited by 15 publications

References 48 publications

A semi‐monolithic detector providing intrinsic DOI‐encoding and sub‐200 ps CRT TOF‐capabilities for clinical PET applications

A semi‐monolithic detector providing intrinsic DOI‐encoding and sub‐200 ps CRT TOF‐capabilities for clinical PET applications

Timing evaluation of a PET detector block based on semi‐monolithic LYSO crystals

Improving the Timing Resolution of Positron Emission Tomography Detectors using Boosted Learning -- A Residual Physics Approach

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