Journal of X-Ray Science and Technology - Volume 25, issue 4

Authors: Trampert, Patrick | Vogelgesang, Jonas | Schorr, Christian | Maisl, Michael | Bogachev, Sviatoslav | Marniok, Nico | Louis, Alfred | Dahmen, Tim | Slusallek, Philipp

Article Type: Research Article

Abstract: BACKGROUND: Laminography is a tomographic technique that allows three-dimensional imaging of flat, elongated objects that stretch beyond the extent of a reconstruction volume. Laminography datasets can be reconstructed using iterative algorithms based on the Kaczmarz method. OBJECTIVE: The goal of this study is to develop a reconstruction algorithm that provides superior reconstruction quality for a challenging class of problems. METHODS: Images are represented in computer memory using coefficients over basis functions, typically piecewise constant functions (voxels). By replacing voxels with spherically symmetric volume elements (blobs) based on generalized Kaiser-Bessel window functions, we obtained an adapted version …of the algebraic reconstruction technique. RESULTS: Band-limiting properties of blob functions are beneficial particular in the case of noisy projections and if only a limited number of projections is available. In this case, using blob basis functions improved the full-width-at-half-maximum resolution from 10.2±1.0 to 9.9±0.9 (p value = 2.3·10-4 ). For the same dataset, the signal-to-noise ratio improved from 16.1 to 31.0. The increased computational demand per iteration is compensated for by a faster convergence rate, such that the overall performance is approximately identical for blobs and voxels. CONCLUSIONS: Despite the higher complexity, tomographic reconstruction from computed laminography data should be implemented using blob basis functions, especially if noisy data is expected. Show more

Keywords: Computed laminography, blob basis function, simultaneous algebraic reconstruction technique, SART, Kaiser-Bessel window

DOI: 10.3233/XST-16230

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 533-546, 2017

Authors: Yang, Jiansheng | Yu, Hengyong | Wang, Ge

Article Type: Research Article

Abstract: The interior and exterior problems have been extensively studied in the field of reconstruction of computed tomography (CT) images, which lead to important theoretical and practical results. In this study, we formulate a middle problem of CT image reconstruction, which is more challenging than either the interior or exterior problems. In the middle problem of CT image reconstruction, projection data are measured through and only through the middle dough-like region, so that each projection profile misses data not only internally but also on both sides. For an object with a radially symmetric exterior, we proved that the middle problem could …be uniquely solved if the middle ring-shaped zone is piecewise constant or there is a known sub-region inside this middle region. Then, we designed and evaluated a POCS-based algorithm for middle tomography, which is to reconstruct a middle image only from the available data. Finally, the remaining issues are also discussed for further research. Show more

Keywords: Middle problem, middle tomography, data truncation, limited-angle tomography, image reconstruction, POCS

DOI: 10.3233/XST-16211

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 547-559, 2017

Authors: Cruz, Gloria | Nie, Sheng Dong

Article Type: Research Article

Abstract: In order to diagnose Parkinson disease (PD) at an early stage, it is important to develop a sensitive method for detecting structural changes in the substantia nigra (SN). Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) have become important tools in supporting diagnosis of PD, with findings based on increased apparent diffusion coefficients (ADCs) in basal ganglia and decreased fractional anisotropy (FA) in SN. Based on the hypothesis that a diffusion kurtosis imaging (DKI) theory is a valuable method for PD diagnosis based on the non-Gaussian diffusion of water in biologic systems, the purpose of this study is to …develop an image processing scheme (software) based on Image-J for the facilitating the application of DKI to assist PD diagnosis. Using the new DKI software enables to estimate the diffusional kurtosis and diffusion coefficients, which reflect the structural differences between regions of interest. The experimental results of applying the new software showed that diffusional kurtosis was highly sensitive to microstructural tissue changes, which were not noticeable in the diffusion coefficient values. Thus, the study results may suggest that applying the new image processing software can be useful for assessing tissue structural abnormalities, monitoring and following disease progression. Show more

Keywords: Parkinson’s disease, diffusional kurtosis imaging, substantia nigra

DOI: 10.3233/XST-16214

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 561-571, 2017

Authors: Ali, Imad | Alsbou, Nesreen | Taguenang, Jean-Michel | Ahmad, Salahuddin

Article Type: Research Article

Abstract: The objective of this study is to quantitatively evaluate variations of dose distributions deposited in mobile target by measurement and modeling. The effects of variation in dose distribution induced by motion on tumor dose coverage and sparing of normal tissues were investigated quantitatively. The dose distributions with motion artifacts were modeled considering different motion patterns that include (a) motion with constant speed and (b) sinusoidal motion. The model predictions of the dose distributions with motion artifacts were verified with measurement where the dose distributions from various plans that included three-dimensional conformal and intensity-modulated fields were measured with a multiple-diode-array detector …(MapCheck2), which was mounted on a mobile platform that moves with adjustable motion parameters. For each plan, the dose distributions were then measured with MapCHECK2 using different motion amplitudes from 0–25 mm. In addition, mathematical modeling was developed to predict the variations in the dose distributions and their dependence on the motion parameters that included amplitude, frequency and phase for sinusoidal motions. The dose distributions varied with motion and depended on the motion pattern particularly the sinusoidal motion, which spread out along the direction of motion. Study results showed that in the dose region between isocenter and the 50% isodose line, the dose profile decreased with increase of the motion amplitude. As the range of motion became larger than the field length along the direction of motion, the dose profiles changes overall including the central axis dose and 50% isodose line. If the total dose was delivered over a time much longer than the periodic time of motion, variations in motion frequency and phase do not affect the dose profiles. As a result, the motion dose modeling developed in this study provided quantitative characterization of variation in the dose distributions induced by motion, which can be employed in radiation therapy to quantitatively determine the margins needed for treatment planning considering dose spillage to normal tissue. Show more

Keywords: Motion dose model, motion artifacts, respiratory motion, spread-out, dose distribution

DOI: 10.3233/XST-16223

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 573-583, 2017

Authors: Ayzenshtat, Gennadiy | Prokopiev, Dmitriy | Baidali, Sergey | Tolbanov, Oleg

Article Type: Research Article

Abstract: PURPOSE: This study aims to analyse energy spectra formation in semiconductor X-ray pixel detectors using a simple experimental method. MATERIALS AND METHODS: The calculations were performed for the pixel detectors made of high-resistivity gallium arsenide compensated by chromium GaAs (Cr). A peculiar feature of these detectors is an extremely short lifetime of the holes. When using ordinary detectors with planar electrodes the spectra with high energy resolution could not be observed. In this study, the shape of amplitude spectra of gamma rays were calculated with energy W0  = 60 and 17 keV. The calculations were performed for the pixel detector …of GaAs (Cr) with the thickness of d  = 500μm and pixel pitch of 50μm. The mobility of electrons and holes were assumed to be μn  = 3000 cm2 /Vs, μp  = 300 cm2 /Vs, and the lifetimes were τ n  = 20 ns and τ p  = 1 ns, respectively. RESULTS: It was demonstrated that in the pixel detector, where there was practically no collection of holes and the amplitude spectra occurred with the energy resolution of 3.5 keV. CONCLUSION: The calculations show that energy spectra of the pixel detectors has a high energy resolution at an appropriate polarity applied bias voltage. The calculation results were conformed by the experimental data. Show more

Keywords: GaAs, carrier lifetime, X-ray pixel detectors, X-ray spectroscopy

DOI: 10.3233/XST-16136

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 585-595, 2017

Authors: Zhao, Yongxia | Suo, Hongna | Wu, Yanmin | Zuo, Ziwei | Zhao, Sisi | Cheng, Shujie

Article Type: Research Article

Abstract: OBJECTIVES: Since body mass index (BMI) affects medical imaging quality or noise due to penetration of the radiation through bodies with varying sizes, this study aims to investigate and determine the optimal BMI-adjusted noise index (NI) setting on the contrast-enhanced liver CT scans obtained using 3D Smart mA technology with adaptive statistical iterative reconstruction (ASIR 2.0) algorithm. MATERIALS AND METHODS: A total of 320 patients who had contrast-enhanced liver CT scans were divided into two equal-sized groups: A (18.5 kg/m2 ≤BMI<24.9 kg/m2 ) and B (24.9 kg/m2 ≤ BMI ≤34.9 kg/m2 ). The two groups were randomly divided into four subgroups …with an NI of 11, 13, 15, and 17. All images were reconstructed with 50% ASIR 2.0. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated after the late arterial, portal venous, and equilibrium phases were completed. Images were evaluated by two radiologists using a subjective 0 –5 scale. Mean CT dose index of volume, dose-length product, and effective dose (ED) were calculated and compared using one-way ANOVA. RESULTS: In group A, the best-quality images obtained at the lowest ED were scanned at an NI of 15 in the late arterial phase, and at an NI of 17 in the portal venous and equilibrium phases. In group B, the best results were obtained at an NI of 13 in the late arterial phase, and at an NI of 15 in the portal venous and equilibrium phases. CONCLUSION: Adjusting NI and iterative reconstruction algorithm based on body mass index can help improve image quality on contrast-enhanced liver CT scans, even at low radiation dose. Show more

Keywords: Body mass index, image quality, iterative reconstruction algorithm, noise index, radiation dose

DOI: 10.3233/XST-16222

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 597-611, 2017

Authors: Bhatia, Navnina | Tisseur, David | Létang, Jean Michel

Article Type: Research Article

Abstract: One of the well-recognized challenge of Cone-Beam Computed Tomography (CBCT) is scatter contamination within the projection images. Scatter degrades the image quality by decreasing the contrast, introducing cupping and shading artifacts and thus leading to inaccuracies in the reconstructed values. The higher scatter to primary ratio experienced in industrial applications leads to even more important artifacts. Various strategies have been investigated to manage the scatter signal in CBCT projection data. One of these strategies is to calculate the scatter intensity by deconvolution of primary intensity using Scatter Kernel Superposition (SKS). In this paper, we present an approach combining experimental measurements …and Monte Carlo simulations to estimate the scatter kernels for industrial applications based on the continuously thickness-adapted kernels strategy with a four-Gaussian modeling of kernels. We compare this approach with an experimental technique based on a two-Gaussian modeling of the kernels. The results obtained prove the superiority of a four-Gaussian model to effectively take into account both the contribution of object and detector scattering as compared to a two-Gaussian approach. We also present the parameterisation of the scatter kernels with respect to object to detector distance. This approach facilitates the use of a single geometry for calculation of scatter kernels over the whole magnification range of the acquisition setup. Show more

Keywords: CBCT, Scatter correction, CIVA, industrial NDT

DOI: 10.3233/XST-16185

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 613-628, 2017

Authors: Lifton, J.J.

Article Type: Research Article

Abstract: Beam hardening causes cupping and streaking artifacts in computed tomographic images, the presence of such artifacts can impair both qualitative and quantitative analysis of the reconstructed data. When the scanned object is composed of a single material, it is possible to correct beam hardening artifacts using the linearization method. However, for multi-material objects, an iterative segmentation-based correction algorithm is needed, which is not only computationally expensive, but may also fail if the initial segmentation result is poor. In this study, a new multi-material linearization beam hardening correction method was proposed and evaluated. The new method is fast and implemented in …the same manner as a mono-material linearization. The correction takes approximately 0.02 seconds per projection. Although facing a potential disadvantage of requiring attenuation measurements of one of the object’s constituent materials, applying the new method has demonstrated its capability for a multi-material workpiece with substantial reduction in both cupping and streaking artifacts. For example, the study showed that the absolute cupping artefacts in steel, titanium and aluminum spheres were reduced from 22%, 20% and 20% to 5%, 1% and 0%, respectively. Show more

Keywords: Beam hardening, computed tomography, multi-material, linearization

DOI: 10.3233/XST-16197

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 629-640, 2017

Authors: Li, Haocheng | Hong, Wei | Liu, Yu | Mou, Xuanqin

Article Type: Research Article

Abstract: The objective of this study is to develop and test the feasibility of applying a machine learning method for geometry calibration of angles in micro-tomography systems. Increasing importance of micro-tomography systems are manifested with escalating applications in various scenarios including but not limited to oral and maxillofacial surgery, vascular and intervention radiology, among other specific applications for purposes of diagnosis and treatments planning. There is possibility, however, actual pathology is confused by artifact of tissue structures after volume reconstruction as a result of CT construction errors. A Kernel Ridge Regression algorithm for micro-tomography geometry estimation and its corresponding phantom is …developed and tested in this study. Several projection images of a rotating Random Phantom of some steel ball bearings in an unknown geometry with gantry angle information were utilized to calibrate both in-plane and out-plane rotation of the detector. The described method can also be expanded to calibrate other parameters of CT construction effortlessly. Using computer simulation, the study results validated that geometry parameters of micro-tomography system were accurately calibrated. Show more

Keywords: Kernel ridge regression, cone beam, computed tomography, geometry calibration

DOI: 10.3233/XST-16178

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 641-652, 2017

Authors: Jamsranjav, Erdenetogtokh | Kuge, Kenichi | Ito, Atsushi | Kinjo, Yasuhito | Shiina, Tatsuo

Article Type: Research Article

Abstract: Soft X-ray microscopy has been developed for high resolution imaging of hydrated biological specimens due to the availability of water window region. In particular, a projection type microscopy has advantages in wide viewing area, easy zooming function and easy extensibility to computed tomography (CT). The blur of projection image due to the Fresnel diffraction of X-rays, which eventually reduces spatial resolution, could be corrected by an iteration procedure, i.e., repetition of Fresnel and inverse Fresnel transformations. However, it was found that the correction is not enough to be effective for all images, especially for images with low contrast. In order …to improve the effectiveness of image correction by computer processing, we in this study evaluated the influence of background noise in the iteration procedure through a simulation study. In the study, images of model specimen with known morphology were used as a substitute for the chromosome images, one of the targets of our microscope. Under the condition that artificial noise was distributed on the images randomly, we introduced two different parameters to evaluate noise effects according to each situation where the iteration procedure was not successful, and proposed an upper limit of the noise within which the effective iteration procedure for the chromosome images was possible. The study indicated that applying the new simulation and noise evaluation method was useful for image processing where background noises cannot be ignored compared with specimen images. Show more

Keywords: Soft X-ray, projection microscopy, iteration procedure, noise evaluation

DOI: 10.3233/XST-16201

Citation: Journal of X-Ray Science and Technology, vol. 25, no. 4, pp. 653-665, 2017