Radiation Risks from Exposure to Chest Computed Tomography
Department of Radiology, Walter Reed Army Medical Center, Washington, DC, USA.Seminars in Ultrasound CT and MRI (Impact Factor: 1.2). 02/2010; 31(1):14-28. DOI: 10.1053/j.sult.2009.09.003
Since 1972, when the first clinical computed tomography (CT) scanner was installed, amazing advances in CT technology have spurned its rapid growth and increasing utilization. Although CT scans are often performed for clinically valid indications that enable proper medical decision-making, the introduction of some protocols has outpaced the scientific data supporting their appropriateness. Considering the growing volume of CT scans performed and the appurtenant risks of radiation exposure, any exposure of patients to radiation for unnecessary or undocumented indications is worrisome. In this paper, the radiation risks associated with chest CT in 3 specific scenarios are discussed: (1) lung cancer screening, for which scientific data demonstrating a reduction in lung cancer mortality is lacking; (2) CT coronary artery angiography, for which the peer reviewed scientific literature is in evolution as its clinical utility is defined and expanded; and (3) CT pulmonary angiography, which is now widely utilized as the imaging modality of choice in the diagnosis of pulmonary emboli. The risks and benefits of these studies will be reviewed in light of the population radiation burden and the appropriateness of each examination.
Article: Computed tomography: an overview.[Show abstract] [Hide abstract]
ABSTRACT: Instrumentation for computed tomography (CT) can be put into three categories that are defined in this article. The basis for this categorization depends on the number of detectors and the type of scanning mode used by each. The goal of each generation scanner is to provide a measurement of x-ray absorption coefficients of cross-sectional portions of the anatomy. The technology of each generation is also presented.Radiologic technology 49(4):491-6.
Conference Paper: Obstacle avoidance and positioning control of autonomous mobilerobots[Show abstract] [Hide abstract]
ABSTRACT: Summary form only given. This paper analyzes the motion and control of differential-type mobile robots for autonomous position control and obstacle avoidance. Two control methods are proposed so that the robot autonomously controls its motion and achieves a desired position without colliding with obstacles that could be present in arbitrary positions inside the working area. For both methods the robot is able to avoid obstacles and achieve the desired position, but the trajectories described by the robot are different for both control methods. Considering that the position of the obstacles are not known in advance, trajectory planning is not possible. Therefore a trajectory pruning technique is proposed and implemented after the first run of the robot, to shorten the trajectory of the robot. This pruning technique eliminates those parts of the original trajectory through which the robot passes two or more times. The effectiveness and generalizability of the control methods and trajectory pruning technique are verified experimentally and by computer simulation for different initial positions, different desired positions and different number and locations of obstaclesAdvanced Intelligent Mechatronics '97. Final Program and Abstracts., IEEE/ASME International Conference on; 07/1997
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ABSTRACT: The paper presents control strategies for abnormal operating conditions of AC motor drive systems. These improve the total performance as well as the ruggedness of the system. Two methods to start a rotating motor through state recognition are described. Two cases are distinguished according to whether the back EMF exists or not. In either case, normal operation can be reestablished as fast as possible on return of the power supply following a power interruption. Discussions and experimental results are presented for both failure conditions, based on V/f control and on sensorless field oriented controlPower Conversion Conference - Nagaoka 1997., Proceedings of the; 09/1997
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