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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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Point Spread Function of photon-counting detectors Under Pile-Up Conditions: A Proposed Framework

Point Spread Function of Photon-Counting Detectors Under Pil...

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Conference on Medical Imaging - Physics of Medical Imaging

作者： Leibolda, David van Der Sara, Stefan J. Goordena, Marlies C. Schaarta, Dennis R. Delft Univ Technol Dept Radiat Sci & Technol Delft Netherlands Holland Proton Therapy Ctr Delft Netherlands

ISBN: (数字)9781510649385

ISBN: (纸本)9781510649385;9781510649378

X-ray photon-counting detectors (PCDs) promise to revolutionise medical imaging. For an efficient comparison of detectors of various materials and with different setup choices, reliable detector performance measures are needed. The detector point spread function (PSF) is a commonly used measure, which describes the spatial response of a detector to the irradiation of a single pixel, given the energy spectrum of the source. In the case of an energy-resolving PCD, the detector PSF is typically derived for each energy bin and characterises its resolution. Moreover, it is commonly determined under low count rate conditions, to avoid dead time and pile-up related distortions. Under these assumptions, the PSF can be determined in a straightforward manner, but does not fully characterise the detector under all conditions encountered in clinical practice. This is especially true since the number of registered counts per energy bin depends on both the incident spectrum and the fluence rate, due to pile-up and dead time. We therefore propose a new metric, the differential point spread function (dPSF), which describes the change in the output count rate due to a small change in the input spectrum, for a given combination of incident spectrum and fluence rate. The dPSF can be used to characterise the spectral and spatial performance of a PCD under high fluence rate conditions, i.e., when its response becomes non-linear. We illustrate the use of the dPSF by performing a Monte-Carlo study in which we compare the response of direct-conversion and scintillation-based PCDs at different fluence rates.

关键词： photon-counting detectors X-ray detectors pile-up point spread function energy response medical imaging

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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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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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Spectral Signatures of X-ray Scatter Using Energy-Resolving photon-counting detectors

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SENSORS 2019年第22期19卷 5022-5022页

作者： Lewis, Cale E. Das, Mini Univ Houston Dept Phys Houston TX 77204 USA

Energy-resolving photon-counting detectors (PCDs) separate photons from a polychromatic X-ray source into a number of separate energy bins. This spectral information from PCDs would allow advancements in X-ray imaging, such as improving image contrast, quantitative imaging, and material identification and characterization. However, aspects like detector spectral distortions and scattered photons from the object can impede these advantages if left unaccounted for. Scattered X-ray photons act as noise in an image and reduce image contrast, thereby significantly hindering PCD utility. In this paper, we explore and outline several important characteristics of spectral X-ray scatter with examples of soft-material imaging (such as cancer imaging in mammography or explosives detection in airport security). Our results showed critical spectral signatures of scattered photons that depend on a few adjustable experimental factors. Additionally, energy bins over a large portion of the spectrum exhibit lower scatter-to-primary ratio in comparison to what would be expected when using a conventional energy-integrating detector. These important findings allow flexible choice of scatter-correction methods and energy-bin utilization when using PCDs. Our findings also propel the development of efficient spectral X-ray scatter correction methods for a wide range of PCD-based applications.

关键词： X-ray scatter photon-counting detectors imaging Compton scatter

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Non-uniformity Correction for photon-counting detectors Using Double GANs 15

Non-uniformity Correction for Photon-counting Detectors Usin...

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15th International Meeting on Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine

作者： Fang, Wei Li, Liang Chen, Zhiqiang Tsinghua Univ Dept Engn Phys Beijing 100084 Peoples R China Tsinghua Univ Minist Educ Key Lab Particle & Radiat Imaging Beijing 100084 Peoples R China

ISBN: (数字)9781510628380

ISBN: (纸本)9781510628380

The development of energy-resolving photon-counting detectors provides a new approach for obtaining spectral information in computed tomography. However, the non-uniformity between different photon-counting detector pixels can cause stripe artefacts in projection domain and concentric ring artefacts in image domain. Here we propose a non-uniformity correction method based on two generative adversarial nets (GANs). The first GAN is a conditional GAN and is responsible for ring artifacts estimation in image domain. The first GAN is trained on 2016 AAPM Grand Challenge dataset, with ring artifacts artificially introduced. The second GAN is an ordinary GAN and is responsible for experimental ring artifacts auto-modeling. The second GAN is trained on real ring artifacts removed from experimental images by the first GAN and aims to provide ample and realistic training labels for re-training the first GAN. Experimental results show that GAN can accurately extract the characteristics of ring artefacts and get them removed from original images to get clear images. Besides, GAN can also be used for realistic training label generation thus better improve the performance of ring artifacts estimation network on experimental datasets.

关键词： non-uniformity correction photon-counting detectors generative adversarial nets

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Non-uniformity correction for MARS photon-counting detectors 15

Non-uniformity correction for MARS photon-counting detectors

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15th International Meeting on Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine

作者： Getzin, Matthew Li, Mengzhou Rundle, David S. Butler, Anthony P. Wang, Ge Rensselaer Polytech Inst Dept Biomed Engn 110 8th St Troy NY 12180 USA MARS Bioimaging Ltd Christchurch New Zealand

ISBN: (数字)9781510628380

ISBN: (纸本)9781510628380

X-ray photon-counting detectors (PCDs) become increasingly popular with applications in medical imaging, material science, and other areas. In this paper, we propose a non-uniformity data correction method for photon-counting detectors based on the first and second moment correction. Using three measure datasets, we demonstrate the method's efficacy in reducing spatial variance of pixel counts. The results demonstrate that both open beam and projection data can be corrected to nearly perfect Poisson counting behavior in both time and space when photon flux is in the detector's linear response range.

关键词： Non-uniformity correction spectral x-ray imaging photon-counting detectors

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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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