A study of inter-crystal scatter in dual-layer offset scintillator arrays for brain-dedicated PET scanners

Teimoorisichani, Mohammadreza; Goertzen, Andrew L.

doi:10.1088/1361-6560/ab1503

Cited by 6 publications

(3 citation statements)

References 34 publications

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“…For PET detector designs such as individual crystal readout or multi-layered detector, all interaction positions of ICS events are possible to be measured, and the ICS events can then either be rejected or used by applying an ICS events recovery algorithm to find the first interaction position (Gu et al 2010, Geoffroy et al 2015, Abbaszadeh et al 2018, Peng et al 2018, Hsu et al 2019. Since the sensitivity of a PET scanner will be significantly reduced if the ICS events are rejected, recently lots of efforts had been spent on developing ICS event recovery algorithms to find the first interaction positions of the ICS events for different detector designs (Rafecas et al 2003, Gillam et al 2014, Lee et al 2018, Teimoorisichani and Goertzen 2019 or modelling the ICS process in image reconstruction so as to improve the image quality (Qi et al 1998a, 1998b, Alessio et al 2006, Stute et al 2011, Zeraatkar et al 2011. Since the cost of PET detectors with the capability to measure all interaction positions of ICS events is substantially higher, most current PET scanners still use block detectors, with the ratio of the number of crystals to the number of SiPMs being much larger than 1.…”

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confidence: 99%

The effects of inter-crystal scattering events on the performance of PET detectors

et al. 2019

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The probability of inter-crystal scattering (ICS) events for 511 keV gamma rays in all current scintillation crystals is high and the ICS events degrade the spatial resolution of PET scanners. In this work, Monte Carlo simulations were performed to study the effects of ICS events on the sensitivity and spatial resolution of PET detectors. LaBr3, LYSO, and PWO that represent scintillation crystals of low, medium and high density, respectively, were used. For a point source placed in the middle of two scintillation detectors of 50 × 50 × 20 mm3 and a lower energy threshold (LET) of 350 keV, the probabilities that at least one gamma ray undergoes ICS are 94%, 84% and 76% for LaBr3, LYSO, and PWO, respectively. The ICS events still provide useful spatial information. The full width at half maximum (FWHM), the full width at tenth maximum (FWTM) and the mean absolute error (MAE) of the curve of the mispositioning of a point source caused by ICS events are 0.45, 3.0 and 0.9 mm if the most popular PET scintillator LYSO is used. The MAE is smaller than the spatial resolution of most current PET scanners. The effect of ICS increases as the detector LET increases, scintillator density decreases, and crystal size decreases. The intrinsic spatial resolutions of a pair of LYSO detectors were calculated using curves of the coincidence counts between one column of the crystals in the two detectors and the sum of the coincidence counts between two opposite crystals of the columns in the two detectors that are in line with the point source changing with the source positions. The latter method removes almost all of ICS events. The FWHM (FWTM) intrinsic spatial resolutions obtained by the two methods are 0.40 (2.0) mm and 0.33 (0.8) mm if the crystal size is 0.5 mm, and are 0.8 (3.0) and 0.68 (1.5) mm if the crystal size is 1.0 mm. ICS events have much bigger contributions to the FWTM rather than the FWHM of the intrinsic spatial resolution of PET detectors. The spatial resolution of a PET scanner can still be improved by decreasing the crystal size to as small as 0.5 mm.

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confidence: 99%

The effects of inter-crystal scattering events on the performance of PET detectors

et al. 2019

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“…Effect of ICS on PET image quality has been studied by several groups (Ritzer et al 2017, Teimoorisichani andGoertzen 2019). Accurately determining the true LORs can alleviate spatial blurring, eventually improving spatial resolution and lesion detectability of PET images (Surti and Karp 2018, Zhang et al 2019.…”

Section: Expected Impact Of the Methods On Image Quality Improvementmentioning

confidence: 99%

Inter-crystal scattering event identification using a novel silicon photomultiplier signal multiplexing method

et al. 2023

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Objective. Identifying the inter-crystal scatter (ICS) events and recovering the first interaction position enables the accurate determination of the line-of-response in positron emission tomography (PET). However, conventional silicon photomultiplier (SiPM) signal multiplexing methods based on two-dimensional (2D) charge-division circuits do not allow the detection of multiple gamma-ray interaction positions in a scintillation array coupled with a SiPM array. In this study, we propose a novel multiplexing method that can restore all the individual channel data from a smaller number of multiplexed channels using high-pass filters and neural networks. Approach.The number of output channels is reduced by summing the SiPM signals that have passed through high-pass filters with different time constants. Then, the signal amplitude of each SiPM channel is restored from the combined signal using an artificial neural network. This study explains the principle of this method in detail and demonstrates the results using 4:1 multiplexing as an example. The usefulness of this method was also demonstrated by its application in the identification of ICS events in 1-to-1 coupled LSO-SiPM PET detectors. Main results. The artificial neural network enabled accurate energy estimation for each SiPM channel. One of the high-pass filter sets with the lowest Cramér–Rao lower bound provided the best results, yielding R2 value of 0.99 between the true and estimated signals. The energy and flood histograms generated using the best-estimated signals were in good agreement with the ground truth. Additionally, the proposed method accurately estimated 2D energy deposit distribution in the LSO crystal array, allowing ICS event identification. Significance. The proposed method is potentially useful for ICS event recovery with a reduced number of array signal readout channels from a SiPM array.

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“…However, a significant number of the annihilation photons undergo single or multiple Compton scattering events within pixelated crystal arrays before the final photon interaction occurs, and we call them inter-crystal scatter (ICS) events (Rafecas et al 2003, Yamaya et al 2011, Abbaszadeh et al 2018. ICS events lead to the misalignment of true LORs owing to incorrect localization of the annihilation photons, thereby degrading the PET image contrast, spatial resolution, and lesion detectability (Miyaoka and Lewellen 2000, Teimoorisichani and Goertzen 2019, Zhang et al 2019.…”

Section: Introductionmentioning

confidence: 99%

SiPM signal readout for inter-crystal scatter event identification in PET detectors

Park

Lee

2020

Phys. Med. Biol.

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In positron emission tomography (PET) with pixelated detectors, a significant number of annihilation photons interact with scintillation crystals through single or multiple Compton scattering events. When these partial energy depositions occur across multiple crystal elements, we call them inter-crystal scatter (ICS) events. ICS events lead to incorrect localization of the annihilation photons, thereby degrading the PET image contrast, spatial resolution, and lesion detectability. The accurate identification of ICS events is the first essential step to improve the quality of PET images by rejecting ICS events or recovering ICS events without losing PET sensitivity. In this study, we propose a novel silicon photomultiplier (SiPM) readout method to identify ICS events in one-to-one coupled PET detectors with a reduced number of data acquisition channels. For concept verification, we assembled a PET detector that consists of a 16-channel SiPM array and 4 4 lutetium oxyorthosilicate (LSO) array with a 3.2 mm crystal pitch. The proposed SiPM readout scheme serializes the 16 SiPM anode signals into four pulse train outputs encoded with four increasing time-delays in steps of 250 ns intervals. A Sum signal of the 16 SiPM anodes provides the timing information for time-of-flight measurement and a trigger signal for coincidence detection. A time-over-threshold (TOT) method was applied for obtaining the energy information followed by a subsequent TOT-to-energy calibration. We successfully identified the ICS events and determined their interacted positions and deposited energies by analyzing the digital pulses from the four pulse train output channels. The occurrence rate of ICS events was 10.85% for the 4 × 4 PET detector module with 3.2 mm-pitch LSO crystals. The PET detector yielded an energy resolution of 10.9 0.6% and coincidence timing resolution of 285 12 ps FWHM. We expect that the proposed method can be a useful solution for alleviating the readout burden of SiPM-based PET scanners with ICS event identification capability.

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A study of inter-crystal scatter in dual-layer offset scintillator arrays for brain-dedicated PET scanners

Cited by 6 publications

References 34 publications

The effects of inter-crystal scattering events on the performance of PET detectors

The effects of inter-crystal scattering events on the performance of PET detectors

Inter-crystal scattering event identification using a novel silicon photomultiplier signal multiplexing method

SiPM signal readout for inter-crystal scatter event identification in PET detectors

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