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Method for the Correction of Spectral Distortions in X-Ray photon-counting detectors

IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 2025年 74卷

作者： Jumanazarov, Doniyor Atamurotov, Farruh Xudoynazarov, Egambergan Matyokubov, Khikmatjon Saparbaev, Rakhmon Abdikarimov, Xidoyat Olsen, Ulrik L. New Uzbekistan Univ Sch Engn Tashkent 100007 Uzbekistan Urgench State Univ Dept Phys Urgench 220100 Uzbekistan Tashkent Univ Informat Technol Dept Telecommun Engn Urgench Branch Urgench 220100 Uzbekistan Inha Univ Tashkent Dept Phys Tashkent 220100 Uzbekistan Univ Tashkent Appl Sci Dept Math Tashkent 100149 Uzbekistan Natl Res Univ TIIAME Informat Technol Dept Tashkent 100000 Uzbekistan Mamun Univ Dept Gen Profess Sci Khiva Uzbekistan Urgench State Pedag Inst Urgench 220100 Uzbekistan Urgench State Univ Dept Phys Urgench Uzbekistan Urgench State Univ Dept Interfac Gen Tech Sci Urgench 220100 Uzbekistan Tech Univ Denmark DTU Phys DK-2800 Lyngby Denmark

Energy-resolved photon-counting detectors (PCD) present the ability to enhance material identification in different X-ray radiography and tomography systems employed for industrial and security applications. Their potential has been proven to be higher than the dual-energy scintillator detectors broadly used nowadays. However, detector effects, like photon pileup and charge sharing, distort the energy spectrum in PCDs. These effects lead to a significant performance deterioration of the PCDs when used for material identification where accurate measurements of multienergy linear attenuation coefficients (LACs) are needed. We have proposed a method that rapidly corrects the measured raw LAC curve for significant spectral distortions in the image reconstruction domain. This method is based on polynomial fitting independently for each energy channel. The method has been validated with experimental data, and the calibration of the method is based on attenuation measurements of common materials with usual laboratory X-ray sources, allowing the method to be employed in any X-ray instrument. The experiments present that the method largely enhances the extraction accuracy of the multienergy LACs, making it helpful for industrial, medical, and security purposes where PCDs are used.

关键词： photonics detectors Nonlinear distortion Distortion measurement II-VI semiconductor materials Fluorescence Cadmium compounds Accuracy Sensor phenomena and characterization Computed tomography Data processing methods industrial medical and security applications multienergy X-ray computed tomography (CT) photon-counting detectors quantitative X-ray characterization

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Spectral calibration of photon-counting detectors at high photon flux

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MEDICAL PHYSICS 2022年第10期49卷 6368-6383页

作者： Sidky, Emil Y. Paul, Emily R. Gilat-Schmidt, Taly Pan, Xiaochuan Univ Chicago Dept Radiol 5841 S Maryland Ave Chicago IL 60637 USA Marquette Univ Dept Biomed Engn Milwaukee WI 53233 USA Med Coll Wisconsin Milwaukee WI 53226 USA

Background Calibration of photon-counting detectors (PCDs) is necessary for quantitatively accurate spectral computed tomography (CT), but the calibration process can be complicated by nonlinear flux-dependent physical factors such as pulse pile-up. Purpose This work develops a method for spectral sensitivity calibration of a PCD-based spectral CT system that incorporates nonlinear flux dependence and can thus be employed at high photon flux. Methods A calibration model for the spectral response and polynomial flux dependence is proposed, which incorporates prior x-ray source spectrum and PCD models and that has a small set of parameters for adjusting to the spectral CT system of interest. The model parameters are determined by fitting transmission data from a known object of known composition: a step-wedge phantom composed of different thicknesses of aluminum, a bone equivalent, and polymethyl methacrylate (PMMA), a soft-tissue equivalent. This fitting employs Tikhonov regularization, and the regularization strength and the polynomial order for the intensity modeling are determined by bias and variance analysis. The spectral calibration and nonlinear intensity correction is validated on transmission measurements through a third material, Teflon, at different x-ray photon flux levels. Results The nonlinear intensity dependence is determined to be accurately accounted for with a third-order polynomial. The calibrated spectral CT model accurately predicts Teflon transmission to within 1% for flux levels up to 50% of the detector maximum. Conclusions The proposed PCD calibration method enables accurate physical modeling necessary for quantitative imaging in spectral CT. Furthermore, the model applies to high flux settings so that acquisition times will not be limited by restricting the spectral CT system to low flux levels.

关键词： calibration photon-counting detectors spectrum estimation

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Assessment of multi-energy inter-pixel coincidence counters for photon-counting detectors at the presence of charge sharing and pulse pileup: A simulation study

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MEDICAL PHYSICS 2021年第9期48卷 4909-4925页

作者： Taguchi, Katsuyuki Iwanczyk, Jan S. Johns Hopkins Univ Sch Med Russell H Morgan Dept Radiol & Radiol Sci Baltimore MD USA

Purpose Spectral distortion due to charge sharing (CS) and pulse pileup (PP) in photon-counting detectors (PCDs) degrades the quality of PCD data. We recently proposed multi-energy inter-pixel coincidence counters (MEICC) that provided spectral cross-talk information related to CS. When PP was absent, the normalized Cramer-Rao lower bounds (nCRLBs) of 225-mu m pixel PCDs with MEICC was comparable to those of 450-mu m pixel PCD without MEICC. The aim of this study was to assess the performance of PCDs with MEICC in the presence of both CS and PP using computer simulations. Methods An in-house Monte Carlo program was modified to incorporate the following four temporal elements: (1) A pulse shape with a pulse duration of 20 ns, (2) delays of up to 10 ns in anode arrival times when photons were incident on pixel boundaries, (3) offsets proportional to a vertical separation between the primary and secondary charge clouds at the rate of +/- 4 ns per +/- 100 mu m, and (4) a stochastic fluctuation of anode arrival times for all of the charge clouds with a standard deviation of 2 ns. We assessed the performance of five PCDs, (a)-(f), for three spectral tasks, (A)-(C): (a) The conventional PCD, (b) a PCD with MEICC, (c) a PCD with one coincidence counter (1CC), (d) a PCD with a 3 x 3 analog charge summing scheme (ACS), and (e) a PCD with a 3 x 3 digital count summing scheme (DCS);(A) conventional CT imaging with water (i.e., linear attenuation coefficient maps), (B) water-bone material decomposition, and (C) K-edge imaging with tungsten. The tube current was changed from 1 mA to 1000 mA and the nCRLB was assessed. Results The recorded count rate curves were fitted by the non-paralyzable detection model with the effective deadtime parameter. The best fit was achieved by 25.8 ns for the conventional PCD, 18.6 ns for MEICC and 1CC, 140.5 ns for ACS, and 209.0 ns for DCS. The nCRLBs were strongly dependent on count rates. MEICC provided the best nCRLBs for all of the imaging task

关键词： charge sharing photon-counting CT photon-counting detectors pulse pileup

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Post-reconstruction 3D single-distance phase retrieval for multi-stage phase-contrast tomography with photon-counting detectors

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JOURNAL OF SYNCHROTRON RADIATION 2019年第2期26卷 510-516页

作者： Brun, Francesco Brombal, Luca Di Trapani, Vittorio Delogu, Pasquale Donato, Sandro Dreossi, Diego Rigon, Luigi Longo, Renata Natl Inst Nucl Phys INFN Trieste Div Trieste Italy Univ Trieste Dept Phys Trieste Italy Univ Siena Dept Phys Sci Earth & Environm Siena Italy Natl Inst Nucl Phys INFN Pisa Div Pisa Italy Sincrotrone Trieste SCpA Elettra Trieste Italy

In the case of single-distance propagation-based phase-contrast X-ray computed tomography with synchrotron radiation, the conventional reconstruction pipeline includes an independent 2D phase retrieval filtering of each acquired projection prior to the actual reconstruction. In order to compensate for the limited height of the X-ray beam or the small sensitive area of most modern X-ray photon-counting detectors, it is quite common to image large objects with a multi-stage approach, i.e. several acquisitions at different vertical positions of the sample. In this context, the conventional reconstruction pipeline may introduce artifacts at the margins of each vertical stage. This article presents a modified computational protocol where a post-reconstruction 3D volume phase retrieval is applied. By comparing the conventional 2D and the proposed 3D reconstructions of a large mastectomy specimen (9cm in diameter and 3cm in height), it is here shown that the 3D approach compensates for the multi-stage artifacts, it avoids refined projection stitching, and the image quality in terms of spatial resolution, contrast and contrast-to-noise ratio is preserved.

关键词： X-ray phase contrast computed tomography single-distance phase retrieval photon-counting detectors image artifacts

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Material separation in x-ray CT with energy resolved photon-counting detectors

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MEDICAL PHYSICS 2011年第3期38卷 1534-1546页

作者： Wang, Xiaolan Meier, Dirk Taguchi, Katsuyuki Wagenaar, Douglas J. Patt, Bradley E. Frey, Eric C. Johns Hopkins Univ Dept Radiol & Radiol Sci Baltimore MD 21287 USA Gamma Med Ideas AS N-1364 Oslo Norway Gamma Med Ideas Northridge CA 91324 USA

Purpose: The objective of the study was to demonstrate that, in x-ray computed tomography (CT), more than two types of materials can be effectively separated with the use of an energy resolved photon-counting detector and classification methodology. Specifically, this applies to the case when contrast agents that contain K-absorption edges in the energy range of interest are present in the object. This separation is enabled via the use of recently developed energy resolved photon-counting detectors with multiple thresholds, which allow simultaneous measurements of the x-ray attenuation at multiple energies. Methods: To demonstrate this capability, we performed simulations and physical experiments using a six-threshold energy resolved photon-counting detector. We imaged mouse-sized cylindrical phantoms filled with several soft-tissue-like and bone-like materials and with iodine-based and gadolinium-based contrast agents. The linear attenuation coefficients were reconstructed for each material in each energy window and were visualized as scatter plots between pairs of energy windows. For comparison, a dual-kVp CT was also simulated using the same phantom materials. In this case, the linear attenuation coefficients at the lower kVp were plotted against those at the higher kVp. Results: In both the simulations and the physical experiments, the contrast agents were easily separable from other soft-tissue-like and bone-like materials, thanks to the availability of the attenuation coefficient measurements at more than two energies provided by the energy resolved photon-counting detector. In the simulations, the amount of separation was observed to be proportional to the concentration of the contrast agents;however, this was not observed in the physical experiments due to limitations of the real detector system. We used the angle between pairs of attenuation coefficient vectors in either the 5-D space (for non-contrast-agent materials using energy resolved photon-counting a

关键词： photon-counting detectors CT material separation K-edge spectral CT

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Improving pulse detection in multibin photon-counting detectors

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JOURNAL OF MEDICAL IMAGING 2016年第2期3卷 023505页

作者： Hsieh, Scott S. Pelc, Norbert J. Stanford Univ Dept Radiol 1201 Welch Rd Stanford CA 94305 USA Stanford Univ Dept Elect Engn 350 Serra Mall Stanford CA 94305 USA Stanford Univ Dept Bioengn 443 Via Ortega Stanford CA 94305 USA

Energy-discriminating, photon-counting (EDPC) detectors are attractive for their potential for improved detective quantum efficiency and for their spectral imaging capabilities. However, at high count rates, counts are lost, the detected spectrum is distorted, and the advantages of EDPC detectors disappear. Existing EDPC detectors identify counts by analyzing the signal with a bank of comparators. We explored alternative methods for pulse detection for multibin EDPC detectors that could improve performance at high count rates. The detector signal was simulated in a Monte Carlo fashion assuming a bipolar shape and analyzed using several methods, including the conventional bank of comparators. For example, one method recorded the peak energy of the pulse along with the width (temporal extent) of the pulse. The Cramer-Rao lower bound of the variance of basis material estimates was numerically found for each method. At high count rates, the variance in water material (bone canceled) measurements could be reduced by as much as an order of magnitude. Improvements in virtual monoenergetic images were modest. We conclude that stochastic noise in spectral imaging tasks could be reduced if alternative methods for pulse detection were utilized. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： photon-counting detectors spectral imaging pulse pileup comparators

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Towards large-area photon-counting detectors for spectral x-ray imaging

Towards large-area photon-counting detectors for spectral x-...

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Conference on Medical Imaging - Physics of Medical Imaging

作者： Thuering, Thomas Gkoumas, Spyridon Zambon, Pietro Trueb, Peter Rissi, Michael Di Prima, Flavio Donath, Tilman Sawall, Stefan Amato, Carlo Kachelriess, Marc Broennimann, Christian DECTRIS Ltd Tafernweg 1 CH-5405 Baden Switzerland German Canc Res Ctr Neuenheimer Feld 280 D-69120 Heidelberg Germany

ISBN: (纸本)9781510625440

photon-counting detector technology using directly converting high-Z sensor materials has recently gained popularity in medical imaging due to its capability to reduce patient dose, increase spatial resolution and provide single shot multi energy information. However, in medical imaging applications, the novel technology is not yet widely used due to technical challenges in manufacturing gap-less detectors with large areas. Here, a nearly gap-less, large-area, multi-energy photon counting detector prototype is presented which was built with existing ASIC and sensor technology. It features an active area of 8x8 cm(2), a 1 mm thick cadmium telluride (CdTe) sensor, four independent energy thresholds and a pixel size of 150 lam. Single and multi-threshold imaging performance of the detector is evaluated by assessing various metrics relevant for conventional (polychromatic) and spectral imaging applications. A high detective quantum efficiency (DQE(0)=0.97), a low dark noise threshold (6.5 keV) and a high count rate capability (up to 3x10(8) counts/s/mm(2)) indicate that the detector is optimally suited for conventional medical X-ray imaging, especially for low dose applications. Spectral performance was assessed by acquiring spectra from fluorescence samples, and the results show a high accuracy of energy peak positions (< 1 keV), precise energy resolution (within a few keV) and decent peak-to-background ratios. Spectral absorption measurements of water and iodinated contrast agent, as well as spectral X-ray radiographs of a human hand phantom, decomposed into bone and soft tissue basis images, demonstrate the multi-energy performance of the detector.

关键词： photon-counting detectors CdTe spectral X-ray imaging large-area detector material decomposition

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On the analogy between pulse-pile-up in energy-sensitive, photon-counting detectors and level-crossing of shot noise

On the analogy between pulse-pile-up in energy-sensitive, ph...

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Conference on Medical Imaging - Physics of Medical Imaging

作者： Roessl, Ewald Bartels, Matthias Daerr, Heiner Proksa, Roland Philips GmbH Innovat Technol Res Labs Rontgenstr 24-26 D-22335 Hamburg Germany

ISBN: (纸本)9781510600188

Shot noise processes are omnipresent in physics and many of their properties have been extensively studied in the past, including the particular problem of level crossing of shot noise. Energy-sensitive, photon-counting detectors using comparators to discriminate pulse-heights are currently heavily investigated for medical applications, e.g. for x-ray computed tomography and x-ray mammography. Surprisingly, no mention of the close relation between the two topics can be found in the literature on photon-counting detectors. In this paper, we point out the close analogy between level crossing of shot noise and the problem of determining count rates of photon counting detectors subject to pulse pile-up. The latter is very relevant for obtaining precise forward models for photon-counting detectors operated under conditions of very high x-ray flux employed in clinical x-ray computed tomography. Although several attempts have been made to provide reasonably accurate, approximative models for the registered number of counts in x-ray detectors under conditions of high flux and arbitrary x-ray spectra, see, e.g.,(1) no exact, analytic solution is given in the literature for general continuous pulse shapes. In this paper we present such a solution for arbitrary response functions, x-ray spectra and continuous pulse shapes based on a result from the theory of level crossing.(2) We briefly outline the theory of level crossing including the famous Rice theorem and translate from the language of level crossing to the language of photon-counting detection.

关键词： photon-counting detectors pulse pile-up shot noise level-crossing

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Modeling photon-counting detectors for x-ray CT: spectral response and pulse-pileup effects and evaluation using real data

Modeling photon-counting detectors for x-ray CT: spectral re...

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Conference on Medical Imaging - Physics of Medical Imaging

作者： Cammin, J. Xu, J. Barber, W. C. Iwanczyk, J. S. Hartsough, N. E. Taguchi, K. Johns Hopkins Univ Sch Med Russell H Morgan Dept Radiol & Radiol Sci Baltimore MD 21205 USA Johns Hopkins Univ Dept Biomed Engn Baltimore MD USA DxRay Inc Northridge CA USA

ISBN: (纸本)9780819494429

Spectral computed tomography (CT) with photon-counting detectors (PCDs) has the potential to substantially advance diagnostic CT imaging by reducing image noise and dose to the patient, by improving contrast and tissue specificity, and by enabling molecular and functional imaging. The current PCD technology, however, is limited by two main factors: imperfect energy measurement (spectral response effects, SRE) and limited count rate (pulse-pileup effects, PPE, due to detector dead-times). The overall goal of our research is to develop compensation algorithms for these sources of data distortions, to demonstrate that PCDs are suitable for clinical CT, and to identify key clinical applications for spectral CT with PCDs. We have already developed an iterative compensation scheme that includes a forward projection model of the imaging chain and that can compensate for either SRE or PPE distortions separately by maximizing a penalized log-likelihood function. In this paper we describe the evaluation of a combined, cascaded SRE and PPE model for PCDs and compare the models to data acquired with an experimental table-top PCD-CT system. The separation into count-rate independent effects (SRE) and count-rate dependent effects (PPE) allows cascading the forward model. First, the SRE model is evaluated using low count rates. Then the PPE model is cascaded and the combined SRE+PPE model is evaluated. Several different attenuators were used, including K-edge materials and the models and data were compared for various count-rate conditions.

关键词： computed tomography photon-counting detectors pulse-pileup spectral response

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Performance Analysis for FMCW Ranging Using photon-counting detectors

Performance Analysis for FMCW Ranging Using Photon-Counting ...

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Conference on Lasers and Electro-Optics (CLEO)

作者： Erkmen, Baris I. Dahl, Jason R. Barber, Zeb W. CALTECH Jet Prop Lab Pasadena CA 91109 USA Montana State Univ Spectrum Lab Bozeman MO 59717 USA

We analyze the performance of FMCW ranging with photon-counting detectors. We derive the Cramer-Rao bound, then determine the optimal fraction of signal-arm photons, given a fixed mean number of source-generated photo... 详细信息

ISBN: (纸本)9781557529732

关键词： photon-counting detectors FMCW Cramér-Rao bound

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