Compton coincidence in silicon photon-counting CT detectors

Sundberg, Christel; Danielsson, Mats; Persson, Mats

doi:10.1117/1.jmi.9.1.013501

Cited by 6 publications

(11 citation statements)

References 19 publications

(38 reference statements)

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“…Since the bias voltage affects the electric field in the detector, increasing the bias voltage reduces the time required for the charge carriers to be collected. In this work, a bias voltage of 200 V was used in alignment with our previous publications 8 , 9 . However, this is not necessarily the optimum for maximizing the performance of estimating the time of each pulse.…”

Section: Discussionmentioning

confidence: 99%

“…The required timing resolution to resolve the interactions corresponding to a single incident photon was estimated in our previous work regarding Compton coincidence detection 8 . Based on a 25×25 mm2 detector area as seen from the x-ray source, it was concluded that a time window of ∼1 ps was required given an incident photon flux of 340 Mcps/mm2, corresponding to the maximum CT flux in an intermediate-sized chest image 26 .…”

Section: Discussionmentioning

confidence: 99%

“…energy in a detector with no tungsten shielding using a maximum-likelihood approach. 8 For incident photons of 60 keV, it was shown that, given a set of interactions originating from the same incident photon, the photon energy could be estimated with an accuracy of a few keV. However, due to the high incident photon flux associated with CT, isolating interactions that originate from the same incident photon is difficult.…”

Section: Photoelectric Comptonmentioning

confidence: 99%

“…Throughout this work, the simulated readout electronics was implemented in MATLAB (The Mathworks Inc., Natick, Massachusetts, United States) based on Eqs. ( 4) and (8). The induced current signals were Fourier transformed by applying the discrete Fourier transform and propagated to the output of the CSA based on Eq.…”

Section: Simulated Noisementioning

confidence: 99%

“…Further, the spectral performance will increase since the photon energy can be estimated based on the interaction energies. We have previously presented a method to estimate the incident photon energy in a detector with no tungsten shielding using a maximum-likelihood approach 8 . For incident photons of 60 keV, it was shown that, given a set of interactions originating from the same incident photon, the photon energy could be estimated with an accuracy of a few keV.…”

Section: Introductionmentioning

confidence: 99%

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Timing resolution in double-sided silicon photon-counting computed tomography detectors

et al. 2023

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Purpose: Our purpose is to investigate the timing resolution in edge-on silicon strip detectors for photon-counting spectral computed tomography. Today, the timing for detection of individual x-rays is not measured, but in the future, timing information can be valuable to accurately reconstruct the interactions caused by each primary photon.Approach: We assume a pixel size of 12 × 500 μm 2 and a detector with double-sided readout with low-noise CMOS electronics for pulse processing for every pixel on each side. Due to the electrode width in relation to the wafer thickness, the induced current signals are largely dominated by charge movement close to the collecting electrodes. By employing double-sided readout electrodes, at least two signals are generated for each interaction. By comparing the timing of the induced current pulses, the time of the interaction can be determined and used to identify interactions that originate from the same incident photon. Using a Monte Carlo simulation of photon interactions in combination with a charge transport model, we evaluate the performance of estimating the time of the interaction for different interaction positions.Results: Our simulations indicate that a time resolution of 1 ns can be achieved with a noise level of 0.5 keV. In a detector with no electronic noise, the corresponding time resolution is ∼0.1 ns.Conclusions: Time resolution in edge-on silicon strip CT detectors can potentially be used to increase the signal-to-noise-ratio and energy resolution by helping in identifying Compton scattered photons in the detector.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Photoelectric Comptonmentioning

confidence: 99%

Section: Simulated Noisementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Timing resolution in double-sided silicon photon-counting computed tomography detectors

et al. 2023

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Spectral information content of Compton scattering events in silicon photon counting detectors

Hsieh,

Taguchi

2024

Medical Physics

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BackgroundSilicon (Si) is a possible sensor material for photon counting detectors (PCDs). A major drawback of Si is that roughly two‐thirds of x‐ray interactions in the diagnostic energy range are Compton scattering. Because Compton scattering is an energy‐insensitive process, it is commonly assumed that Compton events retain little spectral information.PurposeTo quantify how much information can be recovered from Compton scattering events in models of Si PCDs.MethodsWe built a simplified model of Si interactions including two interaction mechanisms: photoelectric effect and Compton scattering. We considered three different binning options that represent strategies for handling Compton events: in Compton censoring, all events under 38 keV (the maximum energy possible from Compton scattering for a 120 keV incident photon) were discarded; in Compton counting, all events between 1 and 38 keV were placed into a single bin; in Compton binning, all events were placed into energy bins of uniform width. These were compared to the ideal detector, which always recorded the correct energy (i.e., 100% photoelectric effect). Every photon was assumed to interact once and only once with Si, and the energy bin width was 5 keV. In the primary analysis, the Si detector was irradiated with a 120 kV spectrum filtered by 30 cm of water, with 99.5% of the arriving spectrum above 38 keV so that there was good separation between photoelectric effect and Compton scattering, and the figures of merit were the Cramér–Rao lower bound (CRLB) of the variance of iodine and water basis material decomposition images, as well as the CRLB of virtual monoenergetic images (i.e., linear combinations of material images) that maximize iodine CNR or water CNR. We also constructed a local linear estimator that attains the CRLB. In secondary analyses, we applied other sources of spectral distortion: (1) a nonzero minimum energy threshold; (2) coarser, 10 keV energy bins; and (3) a model of charge sharing.ResultsWith our chosen spectrum, 67% of the interactions were Compton scattering. Consistent with this, the material decomposition variance for the Compton censoring model, averaged over both basis materials, was 258% greater than the ideal detector. If Compton events carried no spectral information, the Compton counting model would show similar variance. Instead, its basis material variance was 103% greater than the ideal detector, implying that Compton counts indeed carry significant spectral information. The Compton binning model had a basis material variance 60% greater than the ideal detector. The Compton binning model was not affected by a 5 keV minimum energy threshold, but the variance increased from 60% to 107% when charge sharing was included and to 78% with coarser energy bins. For optimized CNR images, the average variance was 149%, 12%, and 10% higher than the ideal detector for the Compton censoring, counting, and binning models, reinforcing the hypothesis that Compton counts are useful for detection tasks and that precise energy assignments are not necessary.ConclusionsSubstantial spectral information remains after Compton scattering events in silicon PCDs.

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Imaging performance of a LaBr₃:Ce scintillation detector for photon counting x‐ray computed tomography: Simulation study

Taguchi,

Schaart,

Goorden

et al. 2024

Medical Physics

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BackgroundPhoton counting detectors (PCDs) for x‐ray computed tomography (CT) are the future of CT imaging. At present, semiconductor‐based PCDs such as cadmium telluride (CdTe), cadmium zinc telluride, and silicon have been either used or investigated for clinical PCD CT. Unfortunately, all of them have the same major challenges, namely high cost and limited spectral signal‐to‐noise ratio (SNR). Recent studies showed that some high‐quality scintillators, such as lanthanum bromide doped with cerium (LaBr3:Ce), are less expensive and almost as fast as CdTe.PurposeThe objective of this study is to assess the performance of a LaBr3:Ce PCD for clinical x‐ray CT.MethodsWe performed Monte Carlo simulations and compared the performance of 3 mm thick LaBr3:Ce and 2 mm thick CdTe for PCD CT with x‐rays at 120 kVp and 20–1000 mA. The two PCDs were operated with either a threshold–subtract (TS) counting scheme or a direct energy binning (DB) counting scheme. The performance was assessed in terms of the accuracy of registered spectra, counting capability, and count‐rate‐dependent spectral imaging‐task performance, for conventional CT imaging, water–bone material decomposition, and K‐edge imaging with tungsten as the K‐edge material. The performance for these imaging‐tasks was quantified by nCRLB, that is, the Cramér–Rao lower bound on the variance of basis line‐integral estimation, normalized by the corresponding value of CdTe at 20 mA.ResultsThe spectrum recorded by CdTe was distorted significantly due to charge sharing, whereas the spectra recorded by LaBr3:Ce better matched the incident spectrum. The dead time, estimated by fitting a paralyzable detector model to the count‐rate curves, was 20.7, 15.0, 37.2, and 13.0 ns for CdTe with TS, CdTe with DB, LaBr3:Ce with TS, and LaBr3:Ce with DB, respectively. Conventional CT imaging showed an adverse effect of reduced geometrical efficiency due to optical reflectors in LaBr3:Ce PCD. The nCRLBs (a lower value indicates a better SNR) for CdTe with TS, CdTe with DB, LaBr3:Ce with TS, LaBr3:Ce with DB, and the ideal PCD, were 1.00 ± 0.01, 1.00 ± 0.01, 1.18 ± 0.02, 1.18 ± 0.02, and 0.79 ± 0.01, respectively, at 20 mA. The nCRLBs for water–bone material decomposition, in the same order, were 1.00 ± 0.02, 1.00 ± 0.02, 0.85 ± 0.02, 0.85 ± 0.02, and 0.24 ± 0.02, respectively, at 20 mA; and 0.98 ± 0.02, 0.98 ± 0.02, 1.09 ± 0.02, 0.83 ± 0.02, and 0.24 ± 0.02, respectively, at 1000 mA. Finally, the nCRLBs for K‐edge imaging, the most demanding task among the five, were 1.00 ± 0.02, 1.00 ± 0.02, 0.55 ± 0.02, 0.55 ± 0.02, and 0.13 ± 0.02, respectively, at 20 mA; and 2.45 ± 0.02, 2.29 ± 0.02, 3.12 ± 0.02, 2.11 ± 0.02, and 0.13 ± 0.02, respectively, at 1,000 mA.ConclusionThe Monte Carlo simulations showed that, compared to CdTe with either TS or DB, LaBr3:Ce with DB provided more accurate spectra, comparable or better counting capability, and superior spectral imaging‐task performances, that is, water–bone material decomposition and K‐edge imaging. CdTe had a better performance than LaBr3:Ce for the conventional CT imaging task due to its higher geometrical efficiency. LaBr3:Ce PCD with DB scheme may be an excellent alternative option for CdTe PCD.

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Compton coincidence in silicon photon-counting CT detectors

Cited by 6 publications

References 19 publications

Timing resolution in double-sided silicon photon-counting computed tomography detectors

Timing resolution in double-sided silicon photon-counting computed tomography detectors

Spectral information content of Compton scattering events in silicon photon counting detectors

Imaging performance of a LaBr₃:Ce scintillation detector for photon counting x‐ray computed tomography: Simulation study

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Compton coincidence in silicon photon-counting CT detectors

Cited by 6 publications

References 19 publications

Timing resolution in double-sided silicon photon-counting computed tomography detectors

Timing resolution in double-sided silicon photon-counting computed tomography detectors

Spectral information content of Compton scattering events in silicon photon counting detectors

Imaging performance of a LaBr3:Ce scintillation detector for photon counting x‐ray computed tomography: Simulation study

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Imaging performance of a LaBr₃:Ce scintillation detector for photon counting x‐ray computed tomography: Simulation study