bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging diagnosis and endoscopic treatment for ureteral	fibroepithelial polyp prolapsing into the bladder
Authors: Xu Chuanliang , Zhang Zhensheng , Ye Huamao , Wu Chengyao , Zhang Chao , Zhang Yuanyuan , Wang Yang , Cao Zhi , Wang Huiqing , Xu Weidong , Pan Anyin , Wei Rongchao , Zeng Shuxiong , Sun Yinghao
Published: December 2019

OBJECTIVE: Fibroepithelial polyps of ureter prolapsing into the bladder are a rare urological condition. We report the imaging findings and our experience with endoscopic treatment for ureteral fibroepithelial polyps prolapsing into the bladder.

PATIENTS AND RESULTS: Four patients with frank pain and hematuria were enrolled. Intravenous urography and computed tomography revealed a ureteral mass with filling defects in affected ureter and mild hydronephrosis. Endoscopic examination showed ureteral polyps prolapsing in the bladder. The histopathologic diagnosis on 4 cases was benign fibroepithelial polyps of ureter. The largest polyps (from 4–10 cm in length) were successfully resected and vaporized by Holmium: YAG laser. A double-pigtail ureteral stent at 7F was placed and left for 6 weeks after the procedure. Neither recurrence nor ureter stricture was observed after up to 12 years of follow-up.

CONCLUSIONS: Ureteral malignancy must be excluded in cases where a ureteral mass is detected. Endoscopic management is recommended to minimize morbidity and complications in treatment of ureteral fibroepithelial polyps that prolapse into the bladder.
Transarterial embolization for serious renal hemorrhage following	renal biopsy
Authors: Zeng Dan , Liu Guihua , Sun Xiangzhou , Zhuang Wenquan , Zhang Yuanyuan , Guo Wenbo , Yang Jianyong , Chen Wei
Published: December 2019

The goal of this study is to evaluate the feasibility and efficacy of percutaneous transarterial embolization for the treatment of serious renal hemorrhage after renal biopsy. Nine patients with renal hemorrhage had frank pain and gross hematuria as main symptoms after renal biopsy. Intrarenal arterial injuries and perinephric hematoma were confirmed by angiography in all cases. The arterial injuries led to two types of renal hemorrhage, Type I: severe renal injure or intrarenal renal artery rupture (n=5), with contrast medium spilling out of the artery and spreading into renal pelvis or kidney capsule in angiography; Type II, pseudo aneurysm or potential risk of intrarenal artery injure (n=4), where contrast medium that spilled out of intraartery was retained in the parenchyma as little spots less than 5 mm in diameter in angiography. Transcatheter superselective intrarenal artery embolization was performed with coils or microcoils (Type I intrarenal artery injure) and polyvinyl alcohol particles (Type II injure). The intrarenal arterial injuries were occluded successfully in all patients. Light or mild back or abdominal pain in the side of the embolized kidney was found in three patients following embolization procedures and disappeared 3 days later. Serum creatinine and perinephric hematoma were stable, and gross hematuresis stopped immediately (n=4) or 3–5 days (n=3) after embolization. In conclusions, transcatheter superselective intrarenal artery embolization as a minimally invasive therapy is safe and effective for treatment of serious renal hemorrhage following percutaneous renal biopsy.
An improved distance-driven method for projection and	backprojection
Authors: Miao Chuang , Liu Baodong , Xu Qiong , Yu Hengyong
Published: December 2019

Fast and accurate image reconstruction is the ultimate goal of iterative methods for limited-angle, few-view, interior problems, etc. Recently, a finite-detector-based projection model was proposed for iterative CT reconstructions, which was called area integral model (AIM) and has shown a high spatial resolution but with a high computational complexity. On the other hand, the distance-driven model (DDM) is the state-of-the-art technology to model forward projection and backprojection, which has shown a low computational complexity but relative low spatial resolution than AIM-based method. Inspired by the DDM, here we propose an improved distance-driven model (IDDM), which has a similar computational complexity with the DDM-based method and comparative spatial resolution with the AIM-based method. In an ordered-subset simultaneous algebraic reconstruction technique (OS-SART) framework, the AIM, IDDM and DDM are implemented and evaluated using a sinogram from a phantom experiment on a Discovery CT750 HD scanner. The results show that the computational cost of DDM- and IDDM-based methods is similar, which is 6 to 13~times faster than the AIM-based method assuming the same number of iterations. The spatial resolution of AIM- and IDDM-based method is comparable, which is better than DDM-based method in terms of full-width-of-half-maximum (FWHM).
Practical geometric calibration for helical cone-beam industrial computed tomography
Authors: Zhang Feng , Yan Bin , Li Lei , Xi Xiaoqi , Jiang Hua
Published: December 2019

In helical cone-beam industrial computed tomography (ICT), the reconstructed images may be interfered by geometry artifacts due to the presence of mechanical misalignments. To obtain artifact-free reconstruction images, a practical geometric calibration method for helical scan is investigated based on Noo's analytic geometric calibration method for circular scan. The presented method is implemented by first dividing the whole ascending path of helical scan into several pieces, then acquiring the projections of a dedicated calibration phantom in circular scan at each section point, of which geometry parameters are calculated using Noo's analytic method. At last, the geometry parameters of each projection in a piece can be calculated by those of the two end points of the piece. We performed numerical simulations and real data experiments to study the performance of the presented method. The experimental results indicated that the method can obtain high-precision geometry parameters of helical scan and give satisfactory reconstruction images.
Coherent soft X-ray high-order harmonics using tight-focusing	laser pulses in the gas mixture
Authors: Lu Faming , Xia Yuanqin , Zhang Sheng , Chen Deying , Zhao Yang , Liu Bin
Published: December 2019

We experimentally study the harmonics from a Xe-He gas mixture using tight-focusing femtosecond laser pulses. The spectrum in the mixed gases exhibits an extended cutoff region from the harmonic H21 to H27. The potential explanation is that the harmonics photons from Xe contribute the electrons of He atoms to transmit into the excited-state. Therefore, the harmonics are emitted from He atoms easily. Furthermore, we show that there are the suppressed harmonics H15 and H17 in the mixed gases. The underlying mechanism is the destructive interference between harmonics generated from different atoms. Our results indicate that HHG from Xe-He gas mixture is an efficient method of obtaining the coherent soft X-ray source.
The effect of detector size and energy resolution on image quality	in multi-projection Compton scatter tomography
Authors: Chighvinadze Tamar , Pistorius Stephen
Published: December 2019

The reconstructed electron density image quality is sensitive to the detector size and energy resolution, which contribute to the blurring and noise in the image. This work evaluates optimal values of the detector parameters for a realistic system through analytical simulations of the transverse slice of the dedicated breast CT system geometry. This study introduces a spectroscopic x-ray tomography technique which uses multiple projections to reconstruct electron density images by backprojecting scattered photons over isogonic curves. The reconstruction can be obtained using a single projection yet its quality degrades as the acquisition conditions i.e. detector size and energy resolution deviate from the ideal. The reconstruction quality becomes inconsistent throughout the image due to the data under sampling caused by the finite resolution of the detector. The extension to the multi-projection mode effectively fills-in the missing data space and improves the ability to reconstruct an object. This work demonstrates the possibility to obtain images in the presence of noise.
Ventricular hemodynamics using cardiac computed tomography and	optical flow method
Authors: Lin Yang-Hsien , Huang Yung-Hui , Lin Kang-Ping , Liu Juhn-Cherng , Huang Tzung-Chi
Published: December 2019

Ventricular hemodynamics plays an important role in assessing cardiac function in clinical practice. The aim of this study was to determine the ventricular hemodynamics based on contrast movement in the left ventricle (LV) between the phases in a cardiac cycle recorded using an electrocardiography (ECG) with cardiac computed tomography (CT) and optical flow method. Cardiac CT data were acquired at 120 kV and 280 mA with a 350 ms gantry rotation, which covered one cardiac cycle, on the 640-slice CT scanner with ECG for a selected patient without heart disease. Ventricular hemodynamics (mm/phase) were calculated using the optical flow method based on contrast changes with ECG phases in anterior-posterior, lateral and superior-inferior directions. Local hemodynamic information of the LV with color coating was presented. The visualization of the functional information made the hemodynamic observation easy.
Iterative CT reconstruction via minimizing adaptively reweighted	total variation
Authors: Zhu Lei , Niu Tianye , Petrongolo Michael
Published: December 2019

BACKGROUND: Iterative reconstruction via total variation (TV) minimization has demonstrated great successes in accurate CT imaging from under-sampled projections. When projections are further reduced, over-smoothing artifacts appear in the current reconstruction especially around the structure boundaries.

OBJECTIVE: We propose a practical algorithm to improve TV-minimization based CT reconstruction on very few projection data.

METHOD: Based on the theory of compressed sensing, the L-0 norm approach is more desirable to further reduce the projection views. To overcome the computational difficulty of the non-convex optimization of the L-0 norm, we implement an adaptive weighting scheme to approximate the solution via a series of TV minimizations for practical use in CT reconstruction. The weight on TV is initialized as uniform ones, and is automatically changed based on the gradient of the reconstructed image from the previous iteration. The iteration stops when a small difference between the weighted TV values is observed on two consecutive reconstructed images.

RESULTS: We evaluate the proposed algorithm on both a digital phantom and a physical phantom. Using 20 equiangular projections, our method reduces reconstruction errors in the conventional TV minimization by a factor of more than 5, with improved spatial resolution.

CONCLUSIONS: By adaptively reweighting TV in iterative CT reconstruction, we successfully further reduce the projection number for the same or better image quality.
Impact of physician practice on patient radiation dose during CT	guided biopsy procedures
Authors: Weir Victor J. , Zhang Jie , Bruner Angela P.
Published: December 2019

PURPOSE: Patient radiation dose during Computed Tomography (CT) guided biopsy procedures is determined by both acquisition technical parameters and physician practice. The potential effect of the physician practice is of concern. This study is to investigate the effects of those intangibles on patient radiation dose.

METHODS: Patient radiation dose from 252 patients who underwent CT guided biopsy from 2009 to 2010 were retrospectively studied. Ten physicians who used conventional intermittent shots, low mA dose saving feature, or both were included in the study. The patient dose reports were retrieved and the total dose length products (DLPs) were analyzed. Linear regression analysis performed between various variables and reported dose. Patient detriment index (PDI) was developed, which sets threshold (standard of practice) for comparing physician practice with their peers. Odds ratio was calculated to determine odds of a group of patients receiving dose above threshold when compared to another group.

RESULTS: Median DLP among ten physicians was 1194 mGy-cm. There was a significant difference (p< 0.01) between reported DLPs doses when physicians used dose saving feature vs. when feature not used (539.8 ± 169.4 mGy-cm vs. 1269.7 ± 659.0 mGy-cm). In general, physicians who used dose saving feature had lower relative PDIs (< 1) compared to the PDIs (> 1) without the dose feature. Odds ratio estimate of 7.7 at 95% confidence level indicates that the odds of a group receiving a high dose depends on practitioner.

CONCLUSION: Adjustments of practice habits, use of dose saving features or both may be needed to improve patient care for CT biopsy.
Theoretical modeling of mobile target broadening in helical and	axial computed tomographic imaging
Authors: Ali Imad , Jackson Steven , Alsbou Nesreen , Ahmad Salahuddin
Published: December 2019

PURPOSE: To investigate variations in mobile target length induced by sinusoidal motion in helical (HCT) and axial CT (ACT) imaging. A mathematical model was derived that predicts the measured broadening of the apparent lengths of mobile targets and its dependence on motion parameters, target size, and imaging couch speed in CT images.

MATERIALS AND METHODS: Three mobile targets of differing lengths and sizes were constructed of tissue-equivalent gel material and embedded into artificial lung phantom. Respiratory motion was mimicked with a mobile phantom that moves in one-dimension along the superior-inferior direction with sinusoidal motion patterns. A mathematical model was derived to predict quantitatively the variations of apparent lengths for mobile targets and its dependence on phantom and imaging couch motion parameters in HCT and ACT. The model predictions were verified by length measurements of the mobile phantom targets that were imaged with the different motion patterns using CT imaging.

RESULTS: The measured lengths of mobile targets enlarged or shrunk depending on the phantom motion parameters that include phantom speed, amplitude, frequency, phase and speed of the imaging couch. The target length variations were significant where some targets doubled lengths or shrunk to less than half of their actual length. The apparent lengths of mobile targets decreased if the target was moving in the same direction as the imaging couch motion and increased if the mobile target was moving opposed to imaging couch in both HCT and ACT. The model predicts well the variations in the mobile target apparent lengths and their dependence on the motion parameters.

CONCLUSION: The measured and model variations of apparent lengths of mobile targets are considerable and may affect the accuracy of tumor volumes obtained from HCT and ACT. This mathematical model provides a method to quantitatively assess the length variations of mobile targets and their dependence on motion parameters of the phantom and imaging system which may have potential applications in the fields of diagnostic imaging and radiotherapy.
Study on image processing of panoramic X-ray using deviation	improvement software
Authors: Kim Tae-Gon , Lee Yang-Sun , Kim Young-Pyo , Park Yong-Pil , Cheon Min-Woo
Published: December 2019

Utilization of panoramic X-ray device is getting wider. Panoramic X-ray has low resolution than general X-ray device and it occurs to distortion by deviation of image synthesis. Due to structural problems, it has been used restrictively to identify of tooth structure, not for whole head. Therefore, it designed and produced panoramic X-ray device which is possible to diagnostic coverage can be extended and had to be adjusted interval control between X-ray generator and image processing for whole of Maxillofacia's diagnosis. Produced panoramic X-ray device is composed basically of short image synthesis. In addition, it was confirmed the results by used the device which was applied deviation of the brightness of the image, filter to improve the location of the deviation and interpolation method.

In this study, it was used 13 images including the front. It occurs to brightness deviation, position deviation, and geometric correction when synthesis of image, but it had been solved by deviation improvement software and a change of CCD camera's scan line which is used for image acquisition. Therefore, it confirmed expansion possibility of utilization range to commonly used panoramic X-ray device.
Combined multi-kernel head computed tomography images optimized	for depicting both brain parenchyma and bone
Authors: Takagi Satoshi , Nagase Hiroyuki , Hayashi Tatsuya , Kita Tamotsu , Hayashi Katsumi , Sanada Shigeru , Koike Masayuki
Published: December 2019

BACKGROUND: The hybrid convolution kernel technique for computed tomography (CT) is known to enable the depiction of an image set using different window settings.

OBJECTIVE: Our purpose was to decrease the number of artifacts in the hybrid convolution kernel technique for head CT and to determine whether our improved combined multi-kernel head CT images enabled diagnosis as a substitute for both brain (low-pass kernel-reconstructed) and bone (high-pass kernel-reconstructed) images.

METHODS: Forty-four patients with nondisplaced skull fractures were included. Our improved multi-kernel images were generated so that pixels of >100 Hounsfield unit in both brain and bone images were composed of CT values of bone images and other pixels were composed of CT values of brain images. Three radiologists compared the improved multi-kernel images with bone images.

RESULTS: The improved multi-kernel images and brain images were identically displayed on the brain window settings. All three radiologists agreed that the improved multi-kernel images on the bone window settings were sufficient for diagnosing skull fractures in all patients.

CONCLUSIONS: This improved multi-kernel technique has a simple algorithm and is practical for clinical use. Thus, simplified head CT examinations and fewer images that need to be stored can be expected.
Optimization of X-ray microplanar beam radiation therapy for	deep-seated tumors by a simulation study
Authors: Shinohara Kunio , Kondoh Takeshi , Nariyama Nobuteru , Fujita Hajime , Washio Masakazu , Aoki Yukimasa
Published: December 2019

A Monte Carlo simulation was applied to study the energy dependence on the transverse dose distribution of microplanar beam radiation therapy (MRT) for deep-seated tumors. The distribution was found to be the peak (in-beam) dose and the decay from the edge of the beam down to the valley. The area below the same valley dose level (valley region) was decreased with the increase in the energy of X-rays at the same beam separation. To optimize the MRT, we made the following two assumptions: the therapeutic gain may be attributed to the efficient recovery of normal tissue caused by the beam separation; and a key factor for the efficient recovery of normal tissue depends on the area size of the valley region. Based on these assumptions and the results of the simulated dose distribution, we concluded that the optimum X-ray energy was in the range of 100–300 keV depending on the effective peak dose to the target tumors and/or tolerable surface dose. In addition, we proposed parameters to be studied for the optimization of MRT to deep-seated tumors.
Low-mAs X-ray CT image reconstruction by adaptive-weighted	TV-constrained penalized re-weighted least-squares
Authors: Liu Yan , Ma Jianhua , Zhang Hao , Wang Jing , Liang Zhengrong
Published: December 2019

BACKGROUND: The negative effects of X-ray exposure, such as inducing genetic and cancerous diseases, has arisen more attentions.

OBJECTIVE: This paper aims to investigate a penalized re-weighted least-square (PRWLS) strategy for low-mAs X-ray computed tomography image reconstruction by incorporating an adaptive weighted total variation (AwTV) penalty term and a noise variance model of projection data.

METHODS: An AwTV penalty is introduced in the objective function by considering both piecewise constant property and local nearby intensity similarity of the desired image. Furthermore, the weight of data fidelity term in the objective function is determined by our recent study on modeling variance estimation of projection data in the presence of electronic background noise.

RESULTS: The presented AwTV-PRWLS algorithm can achieve the highest full-width-at-half-maximum (FWHM) measurement, for data conditions of (1) full-view 10 mA acquisition and (2) sparse-view 80 mA acquisition. In comparison between the AwTV/TV-PRWLS strategies and the previous reported AwTV/TV-projection onto convex sets (AwTV/TV-POCS) approaches, the former can gain in terms of FWHM for data condition (1), but cannot gain for the data condition (2).

CONCLUSIONS: In the case of full-view 10 mA projection data, the presented AwTV-PRWLS shows potential improvement. However, in the case of sparse-view 80 mA projection data, the AwTV/TV-POCS shows advantage over the PRWLS strategies.
Impact of rare earth element added filters on the X-ray beam	spectra: A Monte Carlo approach
Authors: Eskandarlou Amir , Jafari Amir Abbas , Mohammadi Mohammad , Zehtabian Mehdi , Faghihi Reza , Shokri Abbas , Pourolajal Jalal
Published: December 2019

The effectiveness of added filters including conventional and rare earth materials for dental radiography tasks was investigated using a simulation approach. Current study focuses on the combination of a range of various filters to investigate the reduction of radiation absorbed dose and improving the quality of a radiography image.

To simulate the X-ray beam spectrum, a MCNP5 code was applied. Relative intensity, beam quality, and mean energy were investigated for a typical dental radiography machine. The impact of different rare-earth materials with different thicknesses and tube voltages on the X-ray spectrum was investigated.

For Aluminum as a conventional filter, the modeled X-ray spectra and HVL values were in a good agreement with those reported by IPEM. The results showed that for a 70 kVp voltage, with an increase of the thickness and atomic number of a given added filters, an increase of HVL values were observed. However, with the increase of the attenuator thickness, X-ray beam intensity decreases. For mean energy, different results were observed. It was also found that rare earth made filters reduce high energy X-ray radiation due to k-edge absorption.

This leads to an ideal beam for intra-oral radiography tasks. However, as a disadvantage of rare earth added filters, the reduction of the tube output levels should also be considered.
Voltage-Thickness-Gray imaging physical model in X-ray energy	auto-modulation
Authors: Chen Ping , Han Yan , Pan Jinxiao
Published: December 2019

Energy auto-modulation is an important tool in X-ray imaging, as it can improve the quality and longevity of an x-ray imaging system. Because of the complex nature of imaged objects, X-ray energy auto-modulation may be difficult. If there is a physical model about imaging mechanism, one can forecast the best imaging parameters using a pre-scan that can be fed into this model. This paper offers a physical model, which is called the Voltage-Thickness-Gray (VTG) model. Based on equivalent single-energy, this paper uses the empirical formula of X-ray attenuation and X-ray photon intensity to build this VTG model. Then use linear regression to estimate the model's parameters, by multi-voltage imaging about the steel wedge block. At last, by the experiment of the steel step block, verify this model and forecast the imaging tube voltage. The result shows this model can better reflect X-ray attenuation imaging properties, and can be used to forecast the imaging voltage. Also the forecast precision can achieve 90% or so.
Detection of uric acid depositing in tophaceous gout using a new	dual energy spectral CT technology
Authors: Li Xiaohu , Wang Xu , Yu Yonqqiang , Liu Bin , Cai Jing , Xia Li , Luo Li , Wang Wanqin , Ding Qianyun , Zhang Chao , Wang Jie
Published: December 2019

OBJECTIVE: To assess the feasibility and diagnostic value of detecting uric acid depositing among patients with tophaceous gout using a dual energy CT based Gemstone spectral imaging (GSI) technology for qualitative analysis of uric acid.

METHODS: Thirty one patients with clinically detectable tophaceous gout and 10 healthy volunteers underwent Discovery CT 750 HD scan with GSI mode. We selected four case groups of tophi, muscles, cortical bone, and cancellous bone. Each has a region of interest (ROI) of 10 mm diameter. We then analyzed and compared the difference of CT imaging spectroscopy quantitative parameters including concentration of uric acid, calcium, and water levels. The univariate analysis of variance and independent samples t-test were applied in data analyses.

RESULTS: In case group of tophi base substance, the concentration levels were 1268.8 ± 32.2 mg/cm $^3$ for uric acid (Ca), 19.4 ± 9.5 mg/cm $^3$ for calcium (uric acid), 10.8 ± 9.5 mg/cm $^3$ for calcium (water), and 1171.0 ± 26.8 mg/cm $^3$ for water (calcium), respectively. In cortical bone case group, the four base substance concentration levels changed to 1333.6 ± 83.8 mg/cm $^3$ , 271.1 ± 85.0 mg/cm $^3$ , 262.6 ± 85.4 mg/cm $^3$ , and 1230.8 ± 77.0 mg/cm $^3$ . In muscles case group, the four base substance concentration levels were 1143.5 ± 15.7 mg/cm $^3$ , 12.3 ± 5.0 mg/cm $^3$ , 4.4 ± 1.9 mg/cm $^3$ , and 1054.1 ± 14.6 mg/cm $^3$ . Finally, in cancellous bone case group, the corresponding base substance concentration became 1070.9 ± 26.4 mg/cm $^3$ , 85.1 ± 46.9 mg/cm $^3$ , 77.4 ± 46.7 mg/cm $^3$ , and 988.0 ± 23.4 mg/cm^3. Except tophi and muscle differences between Calcium (uric acid) concentration and differences in Calcium (water) concentration, which were not significantly different (p> 0.29), the remaining group pairwise comparisons of the parameters were significantly different (p < 0.05).

CONCLUSION: Dual-energy spectral CT can detect gout tophi within the peripheral joints of the patients. The quantitative measurement of the tophi concentration provides a new imaging method for quantitatively monitoring clinical outcomes of tophi.
A geometric-sensitivity-difference method improves object	depth-localization for continuous-wave fluorescence diffuse optical tomography:	An in silico study in an axial outward-imaging geometry
Authors: Tokala Krishna T. , Piao Daqing , Xu Guan
Published: December 2019

A geometric-sensitivity-difference (GSD) based reconstruction method is demonstrated in fluorescence diffuse optical tomography (FDOT) for improving the depth-localization of objects. The GSD method optimizes the data-model fit based on paired-measurements between source-detector pairs sharing either the source or the detector channel, as comparing to conventional methods that optimize the data-model fit based on un-paired measurements of individual source-detector pairs. This in silico study is limited to continuous-wave and 2-dimension, for a circular-array outward-imaging geometry of which the native sensitivity of measurement varies strongly with respect to the depth of the object. The outcomes of GSD method are compared to that of two conventional methods: one is the baseline method which does not involve any scheme to compensate the variation of native sensitivity; the other applies a depth-adapted weight to counteract the depth-variance of the native sensitivity. These three methods were evaluated using synthetic data corresponding to the following conditions of the object: (1) Single object with a 3-folds of positive contrast of fluorescence over the background was set at edge-depths of 0.5 mm, 5 mm and 10 mm; (2) Two objects with identical 3-folds of positive or 1/3-folds of negative contrast of fluorescence over the background were set at a fixed edge-depth of 10 mm and different azimuthal separations of 45 degree, 135 degree, and 180 degree; (3) Two objects with identical 3-folds of positive or 1/3-folds of negative contrast of fluorescence over the background were set at a fixed azimuthal separation of 90° and at edge-depths of 0.5 mm, 5 mm and 10 mm. The GSD method outperforms the other two methods in localizing a single anomaly and resolving two anomalies, for the anomaly possessing either the 3 folds positive or 1/3-folds negative contrast of fluorescence over the background. The case of objects with negative contrast over the background has specific implications to imaging zinc-specific fluorophore uptake in prostate.
Fast analytical scatter estimation using graphics processing	units
Authors: Ingleby Harry , Lippuner Jonas , Rickey Daniel W. , Li Yue , Elbakri Idris
Published: December 2019

PURPOSE: To develop a fast patient-specific analytical estimator of first-order Compton and Rayleigh scatter in cone-beam computed tomography, implemented using graphics processing units.

METHODS: The authors developed an analytical estimator for first-order Compton and Rayleigh scatter in a cone-beam computed tomography geometry. The estimator was coded using NVIDIA's CUDA environment for execution on an NVIDIA graphics processing unit. Performance of the analytical estimator was validated by comparison with high-count Monte Carlo simulations for two different numerical phantoms. Monoenergetic analytical simulations were compared with monoenergetic and polyenergetic Monte Carlo simulations. Analytical and Monte Carlo scatter estimates were compared both qualitatively, from visual inspection of images and profiles, and quantitatively, using a scaled root-mean-square difference metric. Reconstruction of simulated cone-beam projection data of an anthropomorphic breast phantom illustrated the potential of this method as a component of a scatter correction algorithm.

RESULTS: The monoenergetic analytical and Monte Carlo scatter estimates showed very good agreement. The monoenergetic analytical estimates showed good agreement for Compton single scatter and reasonable agreement for Rayleigh single scatter when compared with polyenergetic Monte Carlo estimates. For a voxelized phantom with dimensions 128 × 128 × 128 voxels and a detector with 256 × 256 pixels, the analytical estimator required 669 seconds for a single projection, using a single NVIDIA 9800 GX2 video card. Accounting for first order scatter in cone-beam image reconstruction improves the contrast to noise ratio of the reconstructed images.

CONCLUSION: The analytical scatter estimator, implemented using graphics processing units, provides rapid and accurate estimates of single scatter and with further acceleration and a method to account for multiple scatter may be useful for practical scatter correction schemes.
A prior-based metal artifact reduction algorithm for x-ray	CT
Authors: Li Ming , Zheng Jian , Zhang Tao , Guan Yihui , Xu Pin , Sun Mingshan
Published: December 2019

In computed tomography (CT), metal objects in the scanning filed are accompanied by physical phenomenon that causes projections to be inconsistent. These inconsistencies produce bright and dark shadows or streaks in analytically reconstructed images. Interpolation-based metal artifact reduction (MAR) algorithms usually replace the inconsistent projection data by estimating surrogate data based on the surrounding uncorrupted projections. In such cases, secondary artifacts will be generated when the data estimates are inaccurate. Therefore, better projection estimation is critical. This paper proposes an image post-processing strategy to create an intermediate image, named the prior image and better estimates of the surrogate data by forward projecting this prior image. The proposed method consists of three steps based on the forward projection MAR framework. First, metallic implants in the uncorrected images are segmented using a Markov random field model (MRF). Then a prior image is generated via an edge-preserving filter and a recovery procedure of the adjacent anatomical structures. Finally, the projection is completed via forward projecting this prior image and the corrected image is reconstructed by the filtered backprojection (FBP) method. Studies on both phantom and clinical data are carried out to verify the performance of the proposed method. The comparisons with other previous MAR algorithms demonstrate that the proposed MAR method performs better in metal artifact suppression and anatomical structure preservation.
Measurement of X-Ray Spectral Line Wavelengths by Using Two Bragg Reflections
Authors: Rodé A. V. , Maksimchuk A. M. , Sklizkov G. V. , Ridgeley A. , Danson C. , Rizvi N. , Bann R. , Forster E. , Goetz K. , Uschmann I.
Published: December 2019

A novel method of measuring absolute x-ray wavelengths using simultaneous Bragg reflections at two parallel crystal plates of equal atomic spacing is presented. The accuracy of wavelength determination Δλ/λ for this method is discussed and a value of 5 × 10−5is achieved. Absolute wavelengths of L-shell laser-produced spectra of Cu, Ge, As, and Se and M-shell spectra of Gd and Tb have been measured in the wavelength region 7.5–8.5 Å using a quartz (10T0) quasimonolithic crystal blank.
X-Ray Standing Wave Analysis of Highly Perfect Cu Crystals and Electrodeposited Submonolayers of Cd and Tl on Cu Surfaces
Authors: Zegenhagen J. , Materlik G. , Uelhofff W.
Published: December 2019

Experimental requirements for measuring the structure and coverage of adsorbates in the monolayer regime on single crystals with x-ray standing wavefields are discussed in detail along with a thorough description of the theory. The near-surface region of Cu crystals was probed depth selectively by detecting K as well as L fluorescence as a function of fluorescence escape angle. The effects of crystalline imperfections and of dispersive crystal arrangements on the spatial resolution of standing wave measurements are described. Copper crystals with (111) and (100) surface orientation were used as substrates for electrodeposition of Cd and Tl from an aqueous electrolyte using cyclic voltammetry. Submonolayer amounts of Cd and Tl deposited in the underpotential range were investigated on the emerged electrodes with x-ray standing waves keeping the samples under atmospheric pressure, in air, or in inert atmosphere.
Normal-Incidence Multilayer Mirrors for the 120–450 Å Wavelength Region
Authors: Gaponov S. V. , Gusev S. A. , Dubrov V. V. , Kuzmichev A. I. , Luskin B. M. , Salashchenko N. N. , Shevelko A. P. , Slemzin V. A. , Sobelman I. I. , Zabrodin I. G.
Published: December 2019

An electron-beam deposition method is used to fabricate spherical and flat mirrors with a peak reflectivity of 20% for wavelengths between 120 and 450 Å. It is experimentally shown that the fabricated mirrors can be employed to form an image with a resolution of 1 μm for ultrasoft x rays. The possibility of producing intense directional high-temperature plasma radiation by spherical multilayer mirrors is demonstrated. A radiation intensity of 107 W/cm2 around 182 Å has been experimentally obtained in the laser plasma image plane.
Effective Area of the AXAF X-Ray Telescope: Dependence upon Dielectric Constants of Coating Materials
Authors: Elsner R. F. , O'Dell S. L. , Weisskopf M. C.
Published: December 2019

This study examines the dependence of the effective area of the AXAF x-ray telescope, upon the complex dielectric constants of possible mirror coatings, over the energy range 0.1–10 keV. At energies near and above the astrophysically important iron-line complex near 6.7 keV, the effective area is very sensitive to the coating density on the three innermost of the telescope's six mirror pairs. Thus, it is desirable to achieve as high a density as feasible. The telescope's spectral response exhibits sharp features at absorption edges of the coating materials. In view of the exceptional energy resolution of the AXAF spectrometers and uncertainties in reflectivities (especially near absorption edges), the AXAF goal of 1% accuracy requires both precise x-ray calibration of the telescope and improved modeling of the telescope and calibration sources. Presented here in the form of plots, the results are also available (on floppy disks) in tabular form.
Microfocus X-Ray Spectra Measurement
Authors: Rheinländer Jørgen , Gerward Leif , Lindegaard-Andersen Asger , Larsen Jens
Published: December 2019

The applied equipment, the experimental procedures, and the results obtained in the experimental measurement of x-ray spectra from a microfocus x-ray unit are described. The measured spectra of x rays passing through different absorbers are compared to calculated spectra, based on calculation of the linear absorption coefficient, μ, and the spectrum of the incident radiation. The nice fit between the measured and the calculated spectra testifies to the applicability of the presented method for determination of the linear attenuation coefficient. Such calculations form the basis for a more accurate experimental determination of the contrast reducing build-up factor in industrial radiography.
Dynamic X-Ray Diffraction by a Multilayer Mirror Modulated with a Transverse Acoustic Wave
Authors: Aristov V. V. , Erko A. I. , Martynov V. V.
Published: December 2019

Dynamic diffraction of an x-ray plane wave by a multilayer mirror modulated with a transverse acoustic wave is analyzed on the basis of rigorous multiwave mode theory. Particular attention is given to the case when λs > τ. where λs is the acoustic wavelength and τ is the extinction length. It has been derived that with increasing sound amplitude, splitting arises in every point of the kinematic branch interaction for both λs < τ and λs > τ. Accordingly the rocking curve takes the form of separate rows of peaks of Bragg diffraction into separate orders, the widths of the peaks being smaller than the width of the Bragg mirror image without modulation. The widths decrease with increasing modulation amplitude.
Raman Spectroscopic Analysis of Mo/Si Multilayers
Authors: Allred David D. , Cai Ming , Wang Qi , Hatch Dorian M. , Reyes-Mena A.
Published: December 2019

Raman spectra are reported from MoSi2 polycrystalline powder and soft x-ray Mo/Si multilayers. The sharp lines at 323 and 438 cm−1 are all due to crystalline MoSi2. These lines in the powder sample intensify with annealing. The Raman spectra of as-deposited multilayers shows a broad asymmetric peak, highest at about 480 cm−1. We attribute this to α-Si which is highly disordered. In contrast to α-Si in semiconductor/semiconductor and semiconductor/dielectric multilayers, in the Mo/Si samples the Raman signal can vanish after modest heating. This provides evidence that the composition of the silicon component of the multilayer changes even with 200°C annealing. Further annealing also produces the signature for crystalline MoSi2 in the multilayer samples. This is the first report of the characterization of Mo/Si soft x-ray multilayers by Raman spectroscopy, and it indicates that Raman spectroscopy may be an effective technique for characterizing these soft x-ray multilayers and may be useful in studying their interfaces.
Interference Suppression of X-Ray Scattering under Total External Reflection from Rough Surfaces
Authors: Yu. Karabekov A. , Kozhevnikov I. V. , Fedyukovich V. E.
Published: December 2019

Destructive interference of waves scattered from both interfaces of a thin film deposited onto a rough substrate is theoretically shown to lead to considerable suppression (up to some orders) of x-ray scattering intensity. The conditions that are necessary for the suppression of scattering are discussed.
Power Loading Limitations in Soft X-Ray Projection Lithography
Authors: Hawryluk A. M. , Ceglio N. M.
Published: December 2019

Soft x-ray projection lithography (SXPL) is an attractive technique for the fabrication of high-speed, high-density integrated circuits. In an SXPL stepper, the x-ray imaging mirrors consist of multilayer coatings deposited onto high precision substrates. The stepper is intended to fabricate ultra-high spatial-resolution structures with a minimum feature size of <0.1 μm. To achieve this resolution, the imaging mirrors must maintain a very precise surface figure while being exposed to x radiation. Failure to achieve and maintain the mirror surface figure will distort the wavefront propagating through the imaging system and will degrade system resolution. The required surface figure accuracy for each imaging mirror depends upon the required resolution, the wavelength, and the optical design. For conventional SXPL stepper designs, the total (peak-to-valley) surface figure error budget per mirror is approximately ±1 nm. Due to material properties at soft x-ray wavelengths and practical fabrication considerations, x-ray multilayer mirrors have limited reflectivities. A fraction of the incident x radiation is absorbed in the multilayer coating. This absorbed radiation constitutes a thermal load on the mirror, thereby distorting its shape and compromising the accuracy of its surface figure. In this paper, we analyze the thermally induced distortion on the imaging optics and conclude that the maximum allowable thermal distortion limits the maximum allowable x-ray power transported to the wafer and limits the minimum acceptable multilayer mirror reflectivity. The penalty for either insensitive x-ray resists or inefficient mirror reflectivity is a decrease in system throughput which cannot be compensated with increased source power either collected by condenser optics or generated by the source.
Application of Scanning Microradiography and X-Ray Microtomography to Studies of Bones and Teeth
Authors: Elliott J. C. , Anderson P. , Gao X. J. , Wong F. S. L. , Davis G. R. , Dowker S. E. P.
Published: December 2019

In scanning microradiography (SMR), a thin section is stepped across a 15-μm diameter X-ray beam and the transmitted intensity measured at each point. This technique has permitted more accurate measurements of the spatial variation of the mineral concentration in sections of dentin and enamel than conventional photographic microradiography. Moreover, because the section is not in close contact with an emulsion, SMR allows continuous study while the specimen is bathed in a reaction solution. The present studies have been particularly directed to gaining an understanding of the formation and repair of carious lesions in teeth: one particular puzzle is subsurface demineralization, in which the initial loss of mineral appears to take place some 20 to 50 μm below the tooth surface. SMR studies are reported here on the demineralization in dilute acids and the subsequent partial remineralization in supersaturated calcium phosphate solutions in model systems for dental caries. In order to develop a theoretical model for de- and remineralization of carious lesions, it is necessary to quantify transport processes within the tooth. To this end, we are developing a method of measuring effective diffusion coefficients of strongly X-ray-absorbing ions in water within permeable solids in which the diffusion coefficient varies with position. The method uses sequential concentration/distance profiles determined by SMR. As a test, diffusion coefficients of potassium iodide in water within a permeable glass frit have been measured. X-ray microtomography (XMT) can be carried out by adding an axis of rotation to the SMR apparatus. Using this method, linear absorption coefficients, and hence mineral concentrations, can be measured in 15 X 15 X 15-μm3 voxels. This has advantages over SMR in that superposition within the depth of the section and errors in determining its thickness are avoided. XMT studies of de- and remineralization similar to those described above for SMR, and also XMT studies of the variation in mineral concentration in the cortical bone of a rat femur along its length, are reported.
Diffraction-Limited Large X-Ray Optics
Authors: Spiller Eberhard
Published: December 2019

It is shown that the technologies required to produce large normal-incidence multilayer x-ray mirrors with diffraction-limited resolution are now available. Applications of these mirrors in x-ray astronomy and x-ray lithography are discussed.
Ultrashort Ultraviolet Free-Electron Lasers
Authors: Umstadter D. , Yu L. H. , Johnson E. , Li D.
Published: December 2019

In this work we combine elements of chirped pulse amplification (CPA) techniques, now familiar in solid-state lasers, with an amplifier based upon a seeded free-electron laser (FEL). The resulting device would produce amplified pulses of unprecedented brevity at wavelengths shorter than can be currently obtained by any tunable laser system. We use a subharmonically seeded FEL to illustrate the concept. Radiation from a Ti:sapphire laser is frequency-tripled and stretched optically to provide a coherent seed pulse for the FEL. When coupled to an electron beam inside a magnetic wiggler, the seed radiation introduces an additional energy modulation on the electron bunch, which has been prepared with an energy chirp to match the chirp in the optical pulse. The energy modulated electrons are then spatially bunched in a dispersion magnet and introduced to a wiggler configured to be resonant to a harmonic of the seed laser, providing additional frequency multiplication. The coherent radiation produced by these electrons is amplified as it traverses the wiggler and recompressed optically. The preservation of phase coherence provided by this scheme results in a device which can yield 4-fs pulses with 0.3 mJ at a central wavelength of ca. 88 nm, easily the shortest duration amplified pulses produced by any laser. In this paper, we discuss various aspects of the concept, including the generation of short pulses, temporal stretching and compression, and potential applications of the device. The phase distortion during the wide bandwidth FEL amplification is discussed in detail, and is shown to be within the bounds required to produce a 4-fs pulse upon compression.
Application of Graphite Mosaic Monochromator Crystals for X-Ray Transport
Authors: Tompkins Perry A.
Published: December 2019

The Vanderbilt University Free-Electron Laser Program is developing the capability to create near-monochromatic x rays for medical imaging and other purposes. For this experiment we feed back the normal infrared FEL light to collide with the electron beam. This causes Compton backscattering of the incident photons which creates x rays. This paper is particularly focused on the x-ray beam transport to be used with this experiment. This transport must redirect the x-ray beam to match a beam chase located in the accelerator vault ceiling at a 40° angle to the x-ray creation axis. It has been determined that the most efficient way to form this transport is by using multiple reflections from mosaic graphite crystals. Samples of these crystals have been obtained and reflection characteristics are being measured. Flat crystals have been investigated at this point. Curved crystals have also been obtained and these will be measured soon. All of these results will dictate the final form of the beam transport.
Entrance Window Design Parameters for High-Pressure Gas X-Ray Imaging Detectors
Authors: Jordan Lawrence M. , Dibianca Frank A.
Published: December 2019

Gas ionization x-ray detectors operating at pressures up to 100 atm offer inherently high spatial and contrast resolution. However, incorporating the detector x-ray entrance window in a conventional pressure vessel designed for such pressures can result in high primary beam loss in the window and a much reduced overall detective quantum efficiency. The design of a gas chamber cover plate for a strip beam detector which mechanically isolates the x-ray entrance window from the lateral tensile stresses in the chamber body is described. A number of test windows of this design, varying in three geometric parameters—thickness, window curvature, and fillet radius—were fabricated from wrought aluminum [6061-T651 ] and subjected to pressures of up to 400 atm for the purpose of selecting an optimum window for a prototype digital x-ray imaging detector. The experimental data indicate that windows can be designed for a detector admitting a 1.0 cm wide x-ray beam that have rupture pressures exceeding 500 atm while maintaining x-ray transmittances of as much as 93.4% for a 120 kVp tungsten anode spectrum.