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Synchrotron radiation at the Photon Factory for non-invasive coronary angiography: experimental studies
Abstract
Synchrotron radiation available at the Photon Factory, National Laboratory for High Energy Physics, provides a new X-ray source which is highly suitable for K-edge subtraction. This is due to its high intensity, its parallelism and its monochromaticity, available in a monochromator system. Experiments were performed using wiggler synchrotron radiation. Since the beam size is relatively-small for in-vivo imaging, a phantom coupled with a detector was moved horizontally using a scanning table. K-edge subtraction was successfully applied both to the coronary artery phantom filled with barium sulphate, and to rat angiography using iodine contrast material. The potential use and value of energy subtraction was successfully demonstrated.
... For example, Chapman presented the idea of diffraction enhanced imaging (DEI) in 1996 [8], and Momose proposed X-ray interferometry-based CT in 1996 [9]. Several medical imaging centers were founded around the world such as the Photon Factory [10], Trieste Synchrotron [11], Grenoble Synchrotron [12], SPring-8 [13], Swiss Light Source [14], Canadian Light Source [15], Australian Synchrotron [16], and Shanghai Synchrotron [17]. Several synchrotron-based X-ray imaging centers were also formed outside synchrotron labs, such as Helsinki [18] and King's College [19]. ...
The basic idea of X-ray dark-field imaging (XDFI), first presented in 2000, was based on the concepts used in an X-ray interferometer. In this article, we review 20 years of developments in our theoretical understanding, scientific instrumentation, and experimental demonstration of XDFI and its applications to medical imaging. We first describe the concepts underlying XDFI that are responsible for imparting phase contrast information in projection X-ray images. We then review the algorithms that can convert these projection phase images into three-dimensional tomographic slices. Various implementations of computed tomography reconstructions algorithms for XDFI data are discussed. The next four sections describe and illustrate potential applications of XDFI in pathology, musculoskeletal imaging, oncologic imaging, and neuroimaging. The sample applications that are presented illustrate potential use scenarios for XDFI in histopathology and other clinical applications. Finally, the last section presents future perspectives and potential technical developments that can make XDFI an even more powerful tool.
... The drive for higher spatial and temporal resolution to capture rapid physiologic changes has led to the development of the micro power contrast injector described in this paper. Prior work in mice and rats [2,131415161718192021 has not fully optimized the methods for small animals. For example, previous images were acquired asynchronous with cardiac or ventilatory cycles, resulting in limited precision in measuring physiologic changes and significant subtraction artifacts. ...
The availability of genetically altered animal models of human disease for basic research has generated great interest in new imaging methodologies. Digital subtraction angiography (DSA) offers an appealing approach to functional imaging in small animals because of the high spatial and temporal resolution, and the ability to visualize and measure blood flow. The micro-injector described here meets crucial performance parameters to ensure optimal vessel enhancement without significantly increasing the total blood volume or producing overlap of enhanced structures. The micro-injector can inject small, reproducible volumes of contrast agent at high flow rates with computer-controlled timing synchronized to cardiopulmonary activity. Iterative bench-top and live animal experiments with both rat and mouse have been conducted to evaluate the performance of this computer-controlled micro-injector, a first demonstration of a new device designed explicitly for the unique requirements of DSA in small animals. Injection protocols were optimized and screened for potential physiological impact. For the optimized protocols, we found that changes in the time-density curves for representative regions of interest in the thorax were due primarily to physiological changes, independent of micro-injector parameters.
Two-dimensional synchrotron radiation (SR) coronary arteriography (CAG) with aortographic contrast injection was considered theoretically and animal experiments were performed to examine its diagnostic ability. This system consisted of a silicon monocrystal, fluorescent plate, avalanche-type pickup tube camera, and image acquisition system. The experiment was performed at synchrotron sources in the Photon Factory in Tsukuba. The x-ray energy was adjusted to just above the iodine K-edge. Theoretical calculation described that the coronary arteries would be demonstrated with a high signal-to-noise ratio by the aortographic CAG with SR. The canine coronary arteries were demonstrated with similar clarity as the selective CAG because coronary arteries with less than a 0.2 mm diameter could be imaged. Without overlap of the left atrium and left ventricle, almost all structures of the coronary arteries could be observed. In addition, the abnormal coronary flow and the coronary arteriovenous fistula of dog were revealed clearly. SR coronary arteriography with aortographic approach provides good visualization of the coronary arteries and detailed information of coronary flow.
K-Edge Subtraction (KES) utilizes the discontinuity in the X-ray absorption across the absorption edge of the selected contrast element and creates an image of the projected density of the contrast element from two images acquired just above and below the K-edge of the contrast element. KES has proved to be powerful in coronary angiography, micro-angiography, bronchography, and lymphatic imaging. X-ray fluorescence imaging is a successful technique for the detection of dilute quantities of elements in specimens. However, its application at high X-ray energies (e.g. at the iodine K-edge) is complicated by significant Compton background, which may enter the energy window set for the contrast material's fluorescent X-rays. Inspired by KES, Fluorescence Subtraction Imaging (FSI) is a technique for high-energy (420 keV) fluorescence imaging using two different incident beam energies just above and below the absorption edge of a contrast element (e.g. iodine). The below-edge image can be assumed as a ''background'' image, which includes Compton scatter and fluorescence from other elements. The above-edge image will contain nearly identical spectral content as the below-edge image but will contain the additional fluorescence of the contrast element. This imaging method is especially promising with thick objects with dilute contrast materials, significant Compton background, and/or competing fluorescence lines from other materials. A quality factor is developed to facilitate the comparison. The theoretical value of the quality factor sets the upper limit that an imaging method can achieve when the noise is Poisson limited. The measured value of this factor makes two or more imaging methods comparable. Using the Hard X-ray Micro-Analysis (HXMA) beamline at the Canadian Light Source (CLS), the techniques of FSI and KES were critically compared, with reference to radiation dose, image acquisition time, resolution, signal-to-noise ratios, and quality factor.
The diagnostic potential of two-dimensional aortographic coronary arteriography with synchrotron radiation was examined in dogs.
The experiment was performed at a wiggler beam line by using a silicon monocrystal, fluorescent plate, and avalanche-type camera. The x-ray energy was adjusted to just above the iodine K-edge to obtain the highest contrast. Quantitative densitometry was used to compare intravenous coronary arteriography with aortographic coronary arteriography.
Aortographic coronary arteriography clearly depicted the branches of the coronary arteries such as the left anterior descending coronary artery, circumferential coronary artery, and right coronary artery to sizes of less than 0.2 mm without major overlap of coronary arteries. Intravenous coronary arteriography depicted only the branches of the left anterior descending coronary artery and right coronary artery with poor image quality. The ratio of contrast material dilution was about 2.4 to 3.4 in aortographic procedures, whereas in intravenous procedures it ranged widely from 7.7 to 15.6.
These preliminary investigations indicate that two-dimensional aortographic coronary arteriography with synchrotron radiation promises to be a minimally invasive and easily repeatable method of clearly imaging the coronary arteries.
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