Journal of X-Ray Science and Technology - Volume 12, issue 1
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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 feasibility of using a Kinestatic Charge Detector (KCD) for dual-energy chest radiography is investigated. A KCD is a gas ionization chamber used with a scanning slot-beam geometry. Dual-energy imaging involves acquisition of two images with different mean photon energies which can then be reconstructed using a suitable algorithm to form images of two basis materials, such as bone and soft-tissue. With a KCD, dual-energy imaging may be performed either by taking two separate exposures at…different kVp settings (the dual-kVp method) or by taking a single exposure with the KCD segmented into a front and back region (the split-detector method), as the higher energy photons will be preferentially absorbed in the back region. We have investigated the feasibility of a dual-energy KCD using computer simulations for both dual-kVp and split-detector systems. The theoretically determined contrast resolutions for aluminum and plexiglas were found to be sufficient for clinical diagnosis; however, electronic noise was found to be a major limiting factor. The dual-kVp method was found to yield significant improvements over the split-detector method at high material thicknesses.
Abstract: Traditionally magnetic resonance angiography (MRA) of the carotid arteries has been performed with time-of-flight (TOF) methods, which are limited by flow related artifacts. Contrast enhanced MRA using an intravenously administered gadolinium agent can overcome the limitations of TOF MRA. One contrast enhanced MRA method, projection magnetic resonance digital subtraction angiograph (MRDSA), generates time-resolved angiograms in a manner similar to conventional digital x-ray digital subtraction angiography. This 2D MRDSA method was evaluated on…15 patients suspected of carotid artery disease. The image quality and carotid lesion detection of 2D MRDSA were compared with that of the 2D and 3D TOF methods. It was found that 2D MRDSA was superior to both 2D and 3D TOF for diagnosing carotid arterial diseases.
Abstract: A generally applicable calibration algorithm is developed for dual energy material decomposition in digital x-ray based imaging. The following two facts are employed: 1) the constancy of the difference between the low and high energy intensities when there is no attenuation material and 2) the existence of boneless regions in field of view. Scatter correction is optimally incorporated into the calibration algorithm by requiring that the scatter correction on measured boneless data is consistent with the…scatter-free body matrix. Experiments in dual chest radiography demonstrated that the new calibration was feasible, the image scatter noise was reduced, and the automated 2D decomposition generated material selective images similar to previous manual decomposition.
Abstract: The aim of this study was to optimize CT scan protocol to minimize patient exposure to ionizing radiation while maintaining CT image quality for detecting pulmonary diseases. The absorbed dose and CT scan quality were determined using dose phantoms at various tube current settings (7.5–115 mAs). The relationship between the absorbed radiation dose and CT scan quality were examined. For both 8-mm and 3-mm scanned slice thickness, the homogeneity of CT scans was within the required…range (< 4 HU) at tested tube settings (> 7.5 mAs). However, the noise level of CT scans remained within the acceptance range (< 0.35%) only when the tube current was ≥ 25 mAs. The reduction of tube current from 115 mAs to 40, 25 or 7.5 mAs could decrease the CT Dose Index (CTDI) to 60, 70 or 85%, respectively. The evaluation of CT image quality suggested that there was an inflection point at 25 mAs. When the spiral chest CT scan was employed at a low tube current setting (i.e. 40 or 25 mAs), it maintained satisfactory image quality and reduced the absorbed dose of the patient, therefore protecting patients from ionizing radiation exposure.
Abstract: Current clinical x-ray imaging is based on the attenuation contrast. In order to better explore the phase-contrast inherent in tissue, we propose a dual detector approach for reconstruction of x-ray attenuation and phase images of an object. A new phase image reconstruction algorithm is derived for polychromatic x-ray source in a dual-detector configuration. With the dual detector approach investigated in this work, two images are acquired by one x-ray exposure. The 1st image is the attenuation…image of the object. The 2nd image is a phase-contrast image of the object and the 1st detector. Yet the 3rd image reconstructed by the algorithm developed in this work, is the object's phase image, a completely new type of image with a great potential for clinical applications. The analysis conducted in our research showed that the dual detector approach has advantages in reduction of radiation dose and alignment errors, and avoiding the problems with motion artifacts and x-ray exposure reproducibility. The design option for the critical 1st detector is analyzed as well.
Abstract: In micro computer tomography (μCT) and medical CT, X-ray sources are polychromatic. Because of this polychromaticity, Beer's law, which states that the ratio of the attenuated and incoming X-ray beam is exponential with the thickness of the material, is no longer valid. This leads to quantitative and visual errors in the reconstructed images, e.g. cupping and streak artefacts. This paper describes a correction scheme for these artefacts using a bimodal energy model for the source-detector energy…spectrum. In essence, this correction procedure is a linearization technique based on a physical model. Results are obtained for different test objects made of combinations of plexiglas, bone, water, and aluminium. They demonstrate the effectiveness of the bimodal model correcting for the beam hardening artefact in two-, and multi-component systems.
Keywords: microtomography, beam hardening correction, bimodal energy model