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X-Ray Spectrometry - published by
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... is an international journal designed for the diverse community (biomedical, industrial and academic) of users and developers of novel x-ray imaging techniques
Aktuelle wissenschaftliche Fachartikel der
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Cone beam CT (CBCT) imaging technique has found many applications in medical imaging in recent years since it provides three-dimensional image reconstruction with low contrast detectability and high resolution. In CBCT systems, image noise caused by photon counting statistics plays an important role in image quality by affecting low contrast detection and patient dose. In this paper, we studied image noise caused by photon counting statistics with the Feldkamp's cone beam reconstruction algorithm. A noise model based on photon counting detector was developed to provide the noise distribution in 3D image space and the quantitative relationships between image noise level and various CT parameters, including the exposure level, the number of projections, the reconstruction filter and the detector pixel size. Computer simulations of a spherical water phantom were conducted to test the theoretical model. This work provides the noise spatial distribution in cone-beam CT and its relationship with CBCT parameters. It can also provide local noise information for adaptive de-noising in the future.
Content Type Journal Article
Authors
Yan Zhang, Department of Electrical & Computer Engineering, University of Rochester, Rochester, NY 14620, USA
Ruola Ning, Department of Imaging Sciences, University of Rochester, Rochester, NY 14620, USA
Chan-Su (CS), a traditional Chinese medicine, is one of the most potent Chinese medicines currently used in cancer chemoprevention and treatment. However, the molecular mechanism of CS-induced-apoptosis is still unclear. This study investigated the molecular mechanism of CS-induced apoptosis using fluorescence resonance energy transfer (FRET) and confocal fluorescence microscope techniques. CS dose-dependently inhibited cell viability cytotoxicity, which was assayed by Cell Counting Kit (CCK-8) and Hoechst33258 staining. Bax translocation to mitochondria was observed in single living cell transfected with GFP-Bax plasmid. The mitochondrial membrane potential (ΔΨ_{m}) loss was also measured in CS-treated cells. And ASTC-a-1 cell expressed stably with SCAT3 plasmid was used to examine if caspase-3 was activated by CS. z-VAD-fmk, a broad-caspase spectrum inhibitor, was found to significantly reduce the inhibition of CS on the cell viability. Overall, our data demonstrated that CS induced ASTC-a-1cells apoptosis in a dose-dependent manner, and Bax, caspase-3 and mitochondrial stress were involved in CS-induced apoptosis. Our findings extend the knowledge about the cellular signaling mechanisms mediating CS-induced apoptosis.
Content Type Journal Article
Authors
Lei Sun, MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, South China Normal University, Guangzhou 510631, China
Xiao-Ping Wang, Department of Anesthesiology, The First Affiliated Hospital of Jinan University, Guangzhou 510632, China
Tong-Sheng Chen, MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, South China Normal University, Guangzhou 510631, China
Long-Xiang Wang, MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, South China Normal University, Guangzhou 510631, China
A portable EDXRF equipment was employed to analyze pre-Columbian metals (gold, silver and copper objects) and to determine the thickness of gold in the case of gildings. To this aim, the EDXRF equipment was optimized to detect Cu, Au and Ag, and various methods were developed to determine from X-ray spectra (K-lines ratio) the thickness of the gildings. These methods were first tested to measure gilding compositions and thicknesses of pens and decorative objects. Then pre-Columbian metals were analyzed, such as gold, silver, copper, gilded copper and gilded silver objects from the Royal Tomb of Sipán and from the Museum of Sicán, in the north of Peru.
Content Type Journal Article
Authors
Roberto Cesareo, Dipartimento di Matematica e Fisica, Università di Sassari, Sassari, Italy
Antonio Brunetti, Dipartimento di Matematica e Fisica, Università di Sassari, Sassari, Italy
The polychromatic spectrum of photons emitted by an X-ray tube in medical diagnostic CT system brings beam hardening artifact. Although many correction methods have been developed, it is still the major artifact in clinical CT imaging. Motivated by CT reconstruction researches benefiting from mathematical phantoms, one so-called physical mathematical phantom and its projection simulation are presented in this paper, which are used in comprehensive evaluation of beam hardening corrections. Due to the inherent merits as compared to discrete and stochastic simulations, an analytic method is proposed to simulate the polychromatic projections of FORBILD head phantom. Firstly, CT-numbers are mapped to material compositions under the precondition sub-regions represent different human tissues. Second, boundary parameters of sub-regions are determined by the presented algorithms. Finally, projections are calculated according to X-ray energy spectrum. For validating the usefulness of our simulation, several typical correction methods are analyzed using simulated projections. The performance of every correction is exhibited distinctly. The analysis results show that there are still the spaces to improve those correction methods.
Content Type Journal Article
Authors
Shaojie Tang, Institute of Image Processing & Pattern Recognition, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, P.R. China
Xuanqin Mou, Institute of Image Processing & Pattern Recognition, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, P.R. China
Ying Yang, Institute of Image Processing & Pattern Recognition, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, P.R. China
Qiong Xu, Institute of Image Processing & Pattern Recognition, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, P.R. China
Hengyong Yu, Biomedical Imaging Division, VT-WFU School of Biomedical Engineering and Science, Virginia Tech., Blacksburg, VA 240601, USA
Coal is one of the most abundant energy resources and has the capability to meet future energy needs with high reliability. The basic knowledge of coal structure is crucial to an understanding of the physical properties of coal and chemistry of conversion processes such as gasification, liquefaction, combustion and carbonization. Coal samples from Makum coalfield, Assam, India were investigated by X-ray diffraction techniques. The highly diffuse X-ray diffraction profiles indicate that the coals have amorphous carbon in their structures. Some of the X-ray structural parameters were evaluated by a semi-quantitative method. The parameters determine were d_{002}, d_{10}, L_{a} and L_{c} of various carbon contents (wt%) of different collieries. Strong linear relationship of d_{002} with the wt% of carbon of the coals was observed. The present study reveals that the Assam coals consist of random layered structures with turbostratic carbons.
Content Type Journal Article
Authors
Binoy K. Saikia, Analytical Chemistry Division, North East Institute of Science & Technology (CSIR), Jorhat-785006, Assam, India
Rajani K. Boruah, Analytical Chemistry Division, North East Institute of Science & Technology (CSIR), Jorhat-785006, Assam, India
Quantitative imaging based on dual energy computed tomography (DECT) is useful in both medical and industrial areas. However, the dependence of the attenuation coefficient on X-ray energy and the polychromatic property of X-ray beams bring obstacles for dual energy image reconstruction. In this paper, attenuation coefficient function μ(E) is approximated with the basis material model. And X-ray spectra which govern the projection functions are estimated from transmission measurements. With these two foundations, we obtain a practical reconstruction method for DECT. The distribution of effective atomic number, electron density, and linear attenuation coefficient at any desirable energy can be reconstructed using the proposed method. Numerical simulations and practical experiments were conducted to evaluate the accuracy and practicability of the method.
Content Type Journal Article
Authors
Guowei Zhang, Lab of Particle Information Acquisition and Processing, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Jianping Cheng, Lab of Particle Information Acquisition and Processing, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Li Zhang, Lab of Particle Information Acquisition and Processing, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Zhiqiang Chen, Lab of Particle Information Acquisition and Processing, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Yuxiang Xing, Lab of Particle Information Acquisition and Processing, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Ling Fu, Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, P.R. China
Shaoqun Zeng, Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, P.R. China
Qingming Luo, Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, P.R. China
Laser Doppler perfusion monitors have been used to study blood flow in tissue. They are useful tools to understand and monitor vascular changes during the treatment of lesions. In addition, lasers have been used in the treatment of cancers through photothermal and photochemical interactions, and the effects of laser treatment in many cases depend on the vasculature of the tumors and their surrounding tissue. In this study, an 805-nm laser was used to non-invasively irradiate subcutaneous mammary and prostatic tumors in rats. The perfusions on the tumor surface, the overlying skin, and underlying muscle tissues were measured using laser Doppler flowmetry during the near-infrared laser treatment. The perfusion probe was fitted into a 16-gauge needle so that the probe could be inserted into the target tissue for the perfusion measurement. The perfusion on the surface of the tumor decreased at the beginning of the laser irradiation, followed by a significant increase. Then, the perfusion was decreased again to a pre-treatment level. The perfusion of the skin tissue and muscle tissue, however, remained relatively unchanged during laser irradiation. Our experimental results indicate that laser photothermal effects could be monitored by the laser Doppler flowmetry and that tumor vascular information could be used to improve the effectiveness of the laser treatment of cancer.
Content Type Journal Article
Authors
Abby Deans, Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73109, USA
Linda Hess, Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73105, USA
Michael Koss, Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73105, USA
Hong Liu, Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, OK 73019, USA
Wei R. Chen, Department of Engineering and Physics, College of Mathematics and Science, University of Central Oklahoma, 100 North University Drive, Edmond, OK 73034, USA
In this paper, we present an alternative derivation and description of Smith's data sufficiency condition for exact cone-beam reconstruction. Different from Smith's condition, our condition with new description can be considered as a bridge between the approximate and exact cone-beam reconstruction. When the data sufficiency condition is satisfied, a set of parallel-beam projections can be obtained for exact 3-D reconstruction. When it is not satisfied, some directional parallel-beam projections will be missed, and only approximate reconstruction is achieved. Although our data sufficiency condition is theoretically proved to be equivalent to Smith's condition, its derivation is totally different.
Content Type Journal Article
Authors
Liang Li, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Kejun Kang, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Zhiqiang Chen, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Li Zhang, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Yuxiang Xing, Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
Hengyong Yu, Biomedical Imaging Division, School of Biomedical Engineering and Science, Virginia Tech, Blacksburg, VA 24061, USA
Ge Wang, Biomedical Imaging Division, School of Biomedical Engineering and Science, Virginia Tech, Blacksburg, VA 24061, USA
Since the introduction of epiluminescence microscopy (ELM), image analysis tools have been extended to the field of dermatology, as an attempt to algorithmically reproduce clinical evaluation. Accurate image segmentation of skin lesions is one of the key steps for useful, early, and non-invasive diagnosis of coetaneous melanomas. This paper proposes an image segmentation algorithm to extract the true border that reveals the global structure irregularity (indentations and protrusions), which may suggest excessive cell growth or regression of a melanoma. The algorithm is applied to the blue channel of the RGB colour vectors to distinguish lesions from the skin and. Analysis of image background is applied by recursive measure of the median and standard deviation of background. This will facilitate automatic and recurring noise reduction and enhancement by image pre-processing. The algorithm also does not depend on the use of rigid threshold values, because an optimal thresholding algorithm "isodata algorithm" that is used determines an optimal threshold iteratively. Experiments are performed on diversity of synthetic skin images that model real hair and lesions of different border irregularities. The aim is to verify the capability of the segmentation algorithm in extracting and characterizing the true features of the processed skin lesions. The next phase of test applies the algorithm to real skin lesions representing high resolution ELM images. We demonstrate that we can enhance and delineate pigmented networks in skin lesions visually, and make them accessible for further analysis and classification.
Content Type Journal Article
Authors
Maher I. Rajab, Computer Engineering Department, University of Umm Al-Qura, P.O. Box 5555, Mecca, Kingdom of Saudi Arabia
The Digital X-ray Scanner System (DX-Scanner) using the Multichannel Ionization Chamber (MIC) has many advantages. On the other hand, the scanned medical image has distorted pixels because of unsuitable integration time at the nonlinear acceleration period and vibration of the AC servo motor during scanning a patient in the system.
This paper proposes a correction algorithm based on fuzzy modeling. The proposed correction algorithm can correct the distorted medical image during scanning. Fuzzy modeling uses a clustering method for the nonlinear motor velocity in the algorithm. The algorithm reconstructs the normal medical image lines by calculating the moving distance every integration time during acceleration period of AC servo motor. The algorithm analyzes by comparing the distance of the acceleration period with the distance of the uniform velocity period in every integration time. The velocity for the acceleration period is able to be compensated via this algorithm. In addition, several image processing procedures are also included in the algorithm.
When the proposed correction algorithm is applied to the test pattern for checking the image resolution, its effectiveness is verified at scanning of 3.5 cm/sec, 7 cm/sec, and 14 cm/sec. The corrected image is a better image.
Content Type Journal Article
Authors
Jaeho Baek, Department of Electrical and Electronic Engineering, Yonsei University, Korea
Mignon Park, Department of Electrical and Electronic Engineering, Yonsei University, Korea
In order to reduce contrast dose and radiation exposure involved in CT angiography, an automatic adaptive control scheme was proposed for bolus chasing, which offers substantial improvements over the conventional constant speed control scheme. In this paper, a manual control scheme is proposed to utilize the expert's knowledge optimally based on real-time imaging feedback. The technical objective is to synchronize the bolus dynamics and the imaging aperture. To test the proposed technique, a realistic simulator is designed, developed and evaluated. It is shown statistically that the manual control outperforms the traditional constant speed control.
Content Type Journal Article
Authors
Henri Bai, Electrical and Computer Engineering Department, Iowa State University, Ames, Lowa 50011, USA
Kai Zeng, Biomedical Engineering Department, University of Iowa, Ames, Lowa 50011, USA
Erwei Bai, Electrical and Computer Engineering Department, University of Iowa, Ames, Lowa 50011, USA
Ge Wang, School of Biomedical Engineering and Science, Virginia Tech, Virginia 24061, USA
In this work, a new contour detection method is studied for detecting brain tumor regions based on their gradient magnitude information. Gradient magnitude data, an edge detection method, is generated from the brain slice image intensity or perceived brightness information. Contour map of the brain tumor is generated by using the gradient magnitude differences of the template masks (cropped from brain slice tumor image) and the sample masks (traverses the image) raw pixel and perceived brightness (luminance) date. Then these differences are averaged and normalized to produce edge profiles of the brain tumor region contours. This data is used by the remote surgical devices for removing the tumor area.
Content Type Journal Article
Authors
Bahar Dirican, Radiation Oncology Department Gulhane Military Medical Academy, Ankara, Turkey
Kaan Oysul, Radiation Oncology Department Gulhane Military Medical Academy, Ankara, Turkey
Alper Pahsa, Radiation Oncology Department Gulhane Military Medical Academy, Ankara, Turkey
Murat Beyzadeoǧu, Radiation Oncology Department Gulhane Military Medical Academy, Ankara, Turkey
Since Katsevich's work on cone-beam CT in 2002, a series of new reconstruction formulae for cone-beam and fan-beam reconstruction have been published. To understand these new results in a unified way, two schemes were proposed in the literature: one is based on the Radon formula, while the other on the Tuy formula. In the paper, we present a general two-step scheme for parallel-, fan- and cone-beam CT based on the inverse Fourier transform. We first derive parallel-beam formulae and then translate them to the divergent-beam case via a standardized method. This complete framework not only provides a single mechanism for the deduction of most existing CT formulae but also generates new algorithms. Meanwhile, along the development of this new framework some minor flaws are identified and fixed in publications. Additionally, the traditional assumption that an object be compactly supported inside a scanning trajectory is no longer needed.
Content Type Journal Article
Authors
Yuchuan Wei, Biomedical Imaging Division, VT-WFU School of Biomedical Engineering and Science, Wake Forest University, Winston-Salem, NC 27157, USA
Hengyong Yu, Biomedical Imaging Division, VT-WFU School of Biomedical Engineering and Science, Virginia Tech, Blacksburg, VA 24061, USA
Jiang Hsieh, Laboratories of Applied Science, GE Healthcare Technologies, Milwaukee, WI 53201, USA
Wenxiang Cong, Biomedical Imaging Division, VT-WFU School of Biomedical Engineering and Science, Virginia Tech, Blacksburg, VA 24061, USA
Ge Wang, Biomedical Imaging Division, VT-WFU School of Biomedical Engineering and Science, Wake Forest University, Winston-Salem, NC 27157, USA
Diffuse optical tomography (DOT) is an emerging imaging modality for non-invasive brain functional mapping. The hemodynamic and metabolic images derived from optical properties are unique and complementary to those of magnetic resonance imaging (MRI) and positron emission tomography (PET). In this paper we present a procedure to optimize the number of sources and detectors as well as mesh size that can be used for image reconstruction in reflectance mode through a series of numerical simulations and tissue-like phantom experiments where both the absorption and scattering images are obtained. In these studies, we also tested the system ability to image a target with small size as well as with low contrast relative to the background medium. Image results were quantitatively analyzed and discussed.
Content Type Journal Article
Authors
Qiang Wang, J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA
Zhao Liu, Department of Pediatrics, Division of Pediatric Neurology, University of Florida, Gainesville, FL 32610, USA
Huabei Jiang, J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA
This paper describes a method for reconstructing 3D frontier points, contour generators and surfaces of anatomical objects or smooth surfaces from a small number, e.g. 10, of conventional 2D X-ray images. The X-ray images are taken at different viewing directions with full prior knowledge of the X-ray source and sensor configurations. Unlike previous works, we empirically demonstrate that if the viewing directions are uniformly distributed around the object's viewing sphere, then the reconstructed 3D points automatically cluster closely on a highly curved part of the surface and are widely spread on smooth or flat parts. The advantage of this property is that the reconstructed points along a surface or a contour generator are not under-sampled or under-represented because surfaces or contours should be sampled or represented with more densely points where their curvatures are high. The more complex the contour's shape, the greater is the number of points required, but the greater the number of points is automatically generated by the proposed method. Given that the number of viewing directions is fixed and the viewing directions are uniformly distributed, the number and distribution of the reconstructed points depend on the shape or the curvature of the surface regardless of the size of the surface or the size of the object. The technique may be used not only in medicine but also in industrial applications.
Content Type Journal Article
Authors
Simant Prakoonwit, School of Systems Engineering, University of Reading, Whiteknights, Reading RG6 6AY, UK
Ralph Benjamin, Visiting professor, concurrently at various UK universities
Bolus-chasing CT angiography is an important new imaging mode for imaging cardiovascular structures and peripheral vessels. The adaptive bolus-chasing method implies a variable pitch spiral cone-beam CT scan. In this paper, we extend 2D-weighted, 3D-weighted and tilted plane FDK algorithms for variable pitch spiral cone-beam CT. Numerical simulation tests with high pitches and large cone angles are performed. Our results demonstrate that the tilted plane Feldkamp-type reconstruction algorithm shows the highest tolerance to the data incompleteness, the 3D-weighted half-scan FDK algorithm is the best choice for the practical variable pitch cone-beam CT, and the exact reconstruction algorithms perform less satisfactorily when a dataset is incomplete. However, the exact algorithms can be used for high accuracy reconstruction offline if a dataset is complete. Our work may facilitate development of practical variable pitch helical cone-beam CT.
Content Type Journal Article
Authors
Jun Zhao, Department of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
Yang Lu, Department of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
Yannan Jin, Department of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
Erwei Bai, Department of Electrical and Computer Engineering, University of Iowa, Iowa City, IA 52242, USA
Ge Wang, Biomedical Imaging Division, VT-WFU School of Biomedical Engineering, Virginia Tech, Blacksburg, VA 24061, USA
Homeostasis in concentration of essential elements and its abnormality due to cancer have been observed for single hair samples by X-ray fluorescence analysis using synchrotron radiation. Ca, Br and K are associated with the cellular signal transduction and were found to have two levels of upper and lower concentrations in hair due to gating their ion channels of hair matrix cells where the channels opened by deficiency of the element. The analysis of patient hair from its root to tip revealed that breast cancer accompanied the characteristic long-period decrease from the upper to the lower level of hair [Ca] that had started 8 to 36 months before finding the cancer; the decreasing profiles were unique to cancer as a competitive process between parathyroid hormone PTH and cancer-induced PTH-related protein by comparison with those for non-cancer subjects. It is concluded that breast cancer originates in disturbance of the signal transduction by the high [Ca] in cells. The observed [Br] in hair gave signs for serious diseases such as renal failure. K deficiency was observed for a half of healthy subjects, similarly to the population of hypertension in Japan. Hair from hypertension patients showed K deficiency, unless taking depressor. Most of elements such as Fe, Cu and Zn in hair were indicators for the liver functions of their storage and excretion.
Content Type Journal Article
Authors
Jun-ichi Chikawa, Center for Advanced Science and Technology, Kouto 3-1-1, Kamigori, Ako, Hyogo, 678-1205, Japan
Kousaku Yamada, Center for Advanced Science and Technology, Kouto 3-1-1, Kamigori, Ako, Hyogo, 678-1205, Japan
Toshio Akimoto, Center for Advanced Science and Technology, Kouto 3-1-1, Kamigori, Ako, Hyogo, 678-1205, Japan
Hiromu Sakurai, Kyoto Pharmaceutical University, Department of Analytical and Bioinorganic Chemistry, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto, 607-8414, Japan
Hiroyuki Yasui, Kyoto Pharmaceutical University, Department of Analytical and Bioinorganic Chemistry, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto, 607-8414, Japan
Hitoshi Yamamoto, Minoh City Hospital, Kayano 5-7-1, Minoh-shi, Osaka, 562-8562, Japan
Shinichirou Okabe, Graduate School of Medicine, Chiba University, Inohana 1-8-1, Chuo-ku, Chiba, 260-8677, Japan
Masaaki Ebara, Graduate School of Medicine, Chiba University, Inohana 1-8-1, Chuo-ku, Chiba, 260-8677, Japan
Recently, the Palamodov algorithm, which was formulated for exact cone-beam reconstruction from data collected along a continuous locus, has been proven to be an excellent approximate algorithm for general cone beam reconstruction. The filtration-backprojection framework of the Palamodov algorithm is efficient for sequential and parallel implementation because its filtration step only involves a 1-D shift-invariant filtering along the tangent direction of the scanning trajectory. On the other hand, the generalized Feldkamp algorithm proposed by Wang et al.~also allows approximate general cone beam reconstruction. In this paper, we report a numerical study comparing these two approximate methods for the cases of helical and saddle curves. In this study, the image quality is evaluated in terms of mean square error (MSE), modulation transform function (MTF), etc. The results demonstrate that the Palamodov algorithm consistently performs similar or better than the generalized Feldkamp algorithm.
Content Type Journal Article
Authors
Kai Zeng, Biomedical Engineering Dept, University of Iowa, 132 Hawkeye court, Iowa city, IA 52246, USA
Hengyong Yu, Biomedical imaging Division, VT-WFU School of Biomedical Engineering & Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
Erwei Bai, Department of Electrical and Computer Engineering, University of Iowa, Iowa city, IA 52246, USA
Ge Wang, Biomedical imaging Division, VT-WFU School of Biomedical Engineering & Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
