Journal of X-Ray Science and Technology - Volume 17, issue 2
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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: Traditional reconstruction algorithm in computed tomography (CT) requires a square reconstruction matrix, regardless of the particular object shape. This becomes inefficient when reconstructing planar objects such as IC chips which have a large area-to-thickness ratio. This article presents a differential reconstruction algorithm for planar object CT scan. By automatically determining the scanning start orientation of the object and its tilting angle with respect to the rotation axis, a reconstruction matrix with different…dimensions and/or different reconstruction resolutions is employed to reconstruct the object area only. For demonstration, a low-temperature co-fire ceramic (LTCC) component is scanned and reconstructed. It shows that the new method requires much less computation time and storage, can achieve higher reconstruction resolution in the thickness dimension, and makes layer separation much easier for multilayer objects.
Abstract: High-energy X-ray computed tomography (CT) systems have been recently used to produce high-resolution images in various nondestructive testing and evaluation (NDT/NDE) applications. The accuracy of the dimensional information extracted from CT images is rapidly approaching the accuracy achieved with a coordinate measuring machine (CMM), the conventional approach to acquire the metrology information directly. On the other hand, CT systems generate the sinogram which is transformed mathematically to the pixel-based images. The dimensional…information of the scanned object is extracted later by performing edge detection on reconstructed CT images. The dimensional accuracy of this approach is limited by the grid size of the pixel-based representation of CT images since the edge detection is performed on the pixel grid. Moreover, reconstructed CT images usually display various artifacts due to the underlying physical process and resulting object boundaries from the edge detection fail to represent the true boundaries of the scanned object. In this paper, a novel algorithm to reconstruct the boundaries of an object with uniform material composition and uniform density is presented. There are three major benefits in the proposed approach. First, since the boundary parameters are reconstructed instead of image pixels, the complexity of the reconstruction algorithm is significantly reduced. The iterative approach, which can be computationally intensive, will be practical with the parametric boundary reconstruction. Second, the object of interest in metrology can be represented more directly and accurately by the boundary parameters instead of the image pixels. By eliminating the extra edge detection step, the overall dimensional accuracy and process time can be improved. Third, since the parametric reconstruction approach shares the boundary representation with other conventional metrology modalities such as CMM, boundary information from other modalities can be directly incorporated as prior knowledge to improve the convergence of an iterative approach. In this paper, the feasibility of parametric boundary reconstruction algorithm is demonstrated with both simple and complex simulated objects. Finally, the proposed algorithm is applied to the experimental industrial CT system data.
Abstract: This paper presents a novel data sufficiency condition that unique and stable ROI reconstruction can be achieved from a more flexible family of data sets. To the interior problem, it allows the ROI (Region-of-interest) can be reconstructed from the line integrals passing through this ROI and a small region B located anywhere as long as the image is known on B. Especially, ROI reconstruction can be achieved without any other a priori knowledge when region B…is placed outside the object support. We also develop a general reconstruction algorithm with the DBP-POCS (Differentiated backprojection-projection onto convex sets) method. Finally, both numerical and real experiments were done to illustrate the new data sufficiency condition and the good stability of the ROI reconstruction algorithm.
Abstract: This paper defines the exact conditions for the application of a previously proposed, general, non-astigmatic, imaging scheme, consisting of a matched pair of spherically bent crystals or reflectors, to x rays. These conditions lead to two specific experimental arrangements, of which one can provide large magnifications. Potential applications include the x-ray diagnosis of laser-produced plasmas and x-ray imaging of, e.g., biological samples, using the highly monochromatic radiation at synchrotron light sources. The…results obtained for x rays are, however, valid for a wide spectrum of the electromagnetic radiation so that, for instance, an application of one of the imaging schemes to lithography in the EUV wavelength range should also be possible, if the spherically bent crystals are replaced by appropriate spherical reflectors. Also described is the design of an x-ray crystal spectrometer, which meets the here defined, necessary requirements for the observation of the x-ray spectra of helium-like argon.
Keywords: Non-astigmatic imaging, large angles of incidence and uniform magnification, imaging of biological samples, EUV lithography, x-ray diagnosis of laser-produced plasmas, monochromatic radiation from synchrotron light sources
Abstract: Micro-CT imaging of objects at very high magnification runs into the problem of small geometric movements of the x-ray emission spot relative to the object, thermally induced or otherwise, causing magnified shifts in the projection images during scanning. This produces movement artefacts in the reconstructed images. Here a technique is described to correct such movements by adding a short reference scan at the end of a high magnification scan, with a very large rotation step. Where…geometry changes during a scan are slow, such movements can be considered minimal during this very short "post-scan". Registration of the post-scan images with corresponding images in the main scan allow X/Y pixel shifts in the projection images associated with the geometry movement to be calculated, and corrected during reconstruction. This post-scan correction method was applied here to scans of three small objects, all with a voxel size less than one micron, in a desktop micro-CT and a nano-CT scanner. The method substantially reduced movement artefacts from the reconstructed images, improving image quality and resolution. Where the geometry movement results largely from thermal movement of the x-ray micro-focus emission spot, the post-scan method allows the reconstruction of the spatio-temporal trajectory of this spot movement.
Abstract: In this paper, we present the preliminary experimental results on controlled cardiac computed tomography (CT), which aims to reduce the motion artifacts by means of controlling the x-ray source rotation speed. An innovative cardiac phantom enables us to perform this experiment without modifying the scanner. It is the first experiment on the cardiac CT with speed controlled x-ray source. Experimental results demonstrate that the proposed method successfully separates the phantom images at different phases (improve…the temporal resolution) through controlling the x-ray speed.