Journal of X-Ray Science and Technology - Volume 12, issue 4
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Journal of X-Ray Science and Technology is an international journal designed for the diverse community (biomedical, industrial and academic) of users and developers of novel x-ray imaging techniques. The purpose of the journal is to provide clear and full coverage of new developments and applications in the field.
Areas such as x-ray microlithography, x-ray astronomy and medical x-ray imaging as well as new technologies arising from fields traditionally considered unrelated to x rays (semiconductor processing, accelerator technology, ionizing and non-ionizing medical diagnostic and therapeutic modalities, etc.) present opportunities for research that can meet new challenges as they arise.
Abstract: The conventional implementation of Katsevich's inversion formula involves the computation of PI segment. This is done by solving a nonlinear equation with a numerical algorithm such as Newton's method. In this study, we develop an implementation of Katsevich's inversion formula without computing PI segment. Our implementation involves a new concept, cone beam cover, which is closely related to PI segment and Tam-Danielsson window. Unlike the implementation based on PI segment, the algorithm complexity of our…implementation can be estimated with several important imaging parameters. This result may be instructive for practical applications to choose scanning parameters and reduce the algorithm complexity. The proposed implementation is validated with satisfactory numerical experiments.
Abstract: Accurate simulation of X-ray transforms of representative objects plays an important role in the evaluation and improvement of CT reconstruction algorithms. In this paper, we formulate the X-ray transform and 3D Radon transform for ellipsoids and tetrahedra, and verify the resulting formulas by numerical simulation. Here the ellipsoids and tetrahedra may be arbitrarily positioned and rotated. Linearity of the first derivative of radon transform is observed. Our results serve as a benchmark for development of various…cone-beam algorithms that work through the Radon space, such as Grangeat-type algorithms.
Abstract: Iterative reconstruction algorithms are well-known to produce high quality images. In this paper, we describe how to make these computationally demanding algorithms feasible in connection with high-resolution, cone-beam x-ray computed tomography (micro-CT) for small animals. First we outline a cost-effective approach that supports distributing the computation across a cluster of inexpensive dual-processor PCs. To a great extent, the limit on the number of cluster nodes that can be used is determined by the overhead…associated with the increased number of interprocessor communications. We then introduce ordered-subsets to accelerate convergence of the reconstruction algorithm thereby reducing the number of required iterations. Finally, we use a method called focus of attention to automatically segment the projection and image data into object and background. By subsequently considering only the object data, we reduce the overall cost of the on-the-fly system matrix computation, the forward and backprojection data updates, and the global reduction operation that facilitates the interprocessor communication. We use the SIRT algorithm to illustrate our work but the methods and results presented apply to iterative reconstruction algorithms in general. The experimental data consists of the three-dimensional Shepp-Logan phantom as well as mouse data obtained from a MicroCAT™ scanner.
Abstract: The use of non-invasive imaging modalities, including micro X-ray computed tomography (micro-CT), is starting to be used extensively to investigate normal and pathological states in a variety of animal models. This increased use of in vivo imaging requires a better understanding of the radiation dose delivered during routine imaging. Our laboratory is equipped with a micro X-ray computer tomography unit (MicroCAT II®, ImTek Inc., Knoxville, TN) with a 60 kVp X-ray source and a reconstruction volume…resolution as low as 15 microns that is used for proton radiation therapy treatment planning. In order to determine the X-ray radiation dose delivered to skin and internal organs by our micro-CT we implanted new, calibrated Harshaw TLD-100 Lithium Fluoride thermo-luminescent detectors (TLDs), into five C57BL/6 male mice and ten Sprague-Dawley male rats. Implants were made into the brain, heart, right lung, liver, stomach, cecum, bladder, dorsal thoracal skin and ventral abdominal skin in each animal. Animals were each scanned once using 50 kVp at 800 μA with 360 projections per scan with each projection lasting 400 msec. Using the TLD readings, the radiation dose from each body location was measured with the dorsal thoracal skin receiving the highest average dose (4.5 cGy, mouse; 2.8 cGy, rat) and other internal organs receiving significantly lower average doses. Therefore, knowing the radiation doses delivered during routine imaging, care can be taken to avoid significant and potentially lethal doses of radiation.
Abstract: A state of the art X-ray micro-CT scanner takes about 20 seconds to acquire a full dataset, which is too slow to capture the rapidly beating heart of small animals. We have been working to develop the first electron-beam micro-CT (EBMCT) prototype for cardiac imaging of the mice and rats. In this paper, we describe the background on electron-beam CT (EBCT) and emphasize the needs for EBMCT. Then, we present a top-level design and a preliminary physical…analysis for the first EBMCT scanner. The proposed EBMCT prototype would allow 0.03–0.01 s temporal resolution (35–70 half-scans per second) with 0.2 mm spatial resolution and 10% contrast resolution. Finally, we discuss a few related issues to further highlight that this project is not only important for basic biomedical research but also feasible technically.
Keywords: electron-beam micro-CT (EBMCT), cone-beam, circular and spiral scanning loci, small animal imaging, cardiac imaging
Abstract: In high-energy transmission industry computed tomography (ICT), convolution back-projection (CBP) is widely used for image reconstruction. But high mass thickness and the requirement of short scanning time lead to high statistical noise. Statistical methods are developed from emission tomography and its potential in transmission tomography has been appreciated recently. Consequently, statistical methods, which model the Possion noise of X-ray photons, are expected to produce better images than transform methods. In order to…use those methods, such as maximum a posteriori (MAP), we need speed up the iterate algorithm and make use of the work-piece's prior information thoroughly. This paper presents a novel prior image model, which we refer to as genetic discrete Markov random filed (GDMRF) model. This model has two useful characters· discrete gray set and the genetic character of gray set. With the discrete gray set, the iterate algorithm is highly active. With the genetic character of GDMRF model, the reconstructed image quality benefits from using prior information thoroughly. Experiment has demonstrated that the GDMRF model is useful for image reconstruction from sinogram with low signal-to-noise ratio (SNR).
Abstract: In clinical x-ray phase imaging, the significant tissue attenuation cannot be ignored. In x-ray phase tomography, the presence of tissue attenuation requires acquisition of at least two images for the retrieval of tissue phase for a given tomographic view. This paper presents an important observation that the same map of the projected electron densities can determine both the phase and attenuation maps of soft tissues, provided that the dominance of incoherent scattering holds. Based on this…observation a new strategy to perform the phase retrieval was developed. A 3-D phase tomography reconstruction formula was derived, which combines the three-dimensional inverse Radon transform with the phase retrievals for soft tissues. This new formula alleviates all the technical difficulties associated with the requirement of acquiring two images per tomographic view for phase-retrievals in x-ray phase tomography.
Abstract: Efforts to improve the spatial resolution of CT scanners have focused mainly on reducing the source and detector element sizes, ignoring losses from the size of the secondary-ionization charge "clouds" created by the detected x-ray photons, i.e., the "physics limit." This paper focuses on implementing a technique called "projective compression," which allows further reduction in effective cell size while overcoming the physics limit as well. Projective compression signifies detector geometries in which the…apparent cell size is smaller than the physical cell size, allowing large resolution boosts. A realization of this technique has been developed with a dual-arm "variable-resolution x-ray" (VRX) detector. Accurate values of the geometrical parameters are needed to convert VRX outputs to formats ready for optimal image reconstruction by standard CT techniques. The required calibrating data are obtained by scanning a rotating pin and fitting a theoretical parametric curve (using a multi-parameter minimization algorithm) to the resulting pin sinogram. Excellent fits are obtained for both detector-arm sections with an average (maximum) fit deviation of ∼0.05 (0.1) detector cell width. Fit convergence and sensitivity to starting conditions are considered. Pre- and post-optimization reconstructions of the alignment pin and a biological subject reconstruction after calibration are shown.