The advent of computed tomography (CT) has revolutionized diagnostic radiology. Since the inception of CT in the 1970s, its use has increased rapidly. It is estimated that more than 62 million CT scans per year are currently obtained in the United States, including at least 4 million for children. By its nature, CT involves larger radiation doses than the more common, conventional x-ray imaging procedures ( Table 1 Typical Organ Radiation Doses from Various Radiologic Studies. We briefly review the nature of CT scanning and its main clinical applications, both in symptomatic patients and, in a more recent development, in the screening of asymptomatic patients. We focus on the increasing number of CT scans being obtained, the associated radiation doses, and the consequent cancer risks in adults and particularly in children. Although the risks for any one person are not large, the increasing exposure to radiation in the population may be a public health issue in the future.

Mortal Kombat 5 Highly Compressed Free Download. CT and Its Use The basic principles of axial and helical (also known as spiral) CT scanning are illustrated in Figure 1 The Basics of CT. A motorized table moves the patient through the CT imaging system. At the same time, a source of x-rays rotates within the circular opening, and a set of x-ray detectors rotates in synchrony on the far side of the patient.

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The x-ray source produces a narrow, fan-shaped beam, with widths ranging from 1 to 20 mm. In axial CT, which is commonly used for head scans, the table is stationary during a rotation, after which it is moved along for the next slice. In helical CT, which is commonly used for body scans, the table moves continuously as the x-ray source and detectors rotate, producing a spiral or helical scan. The illustration shows a single row of detectors, but current machines typically have multiple rows of detectors operating side by side, so that many slices (currently up to 64) can be imaged simultaneously, reducing the overall scanning time. All the data are processed by computer to produce a series of image slices representing a three-dimensional view of the target organ or body region..

Download Manual Book Nikon D3100 Bahasa Indonesia. CT has transformed much of medical imaging by providing three-dimensional views of the organ or body region of interest. The use of CT has increased rapidly, both in the United States and elsewhere, notably in Japan; according to a survey conducted in 1996, the number of CT scanners per 1 million population was 26 in the United States and 64 in Japan. It is estimated that more than 62 million CT scans are currently obtained each year in the United States, as compared with about 3 million in 1980 ( Figure 2 Estimated Number of CT Scans Performed Annually in the United States. The most recent estimate of 62 million CT scans in 2006 is from an IMV CT Market Summary Report.

This sharp increase has been driven largely by advances in CT technology that make it extremely user-friendly, for both the patient and the physician. Common Types of CT Scans CT use can be categorized according to the population of patients (adult or pediatric) and the purpose of imaging (diagnosis in symptomatic patients or screening of asymptomatic patients).

CT-based diagnosis in adults is the largest of these categories. (About half of diagnostic CT examinations in adults are scans of the body, and about one third are scans of the head, with about 75% obtained in a hospital setting and 25% in a single-specialty practice setting. ) The largest increases in CT use, however, have been in the categories of pediatric diagnosis and adult screening, and these trends can be expected to continue for the next few years. The growth of CT use in children has been driven primarily by the decrease in the time needed to perform a scan — now less than 1 second — largely eliminating the need for anesthesia to prevent the child from moving during image acquisition. The major growth area in CT use for children has been presurgical diagnosis of appendicitis, for which CT appears to be both accurate and cost-effective — though arguably no more so than ultrasonography in most cases. Estimates of the proportion of CT studies that are currently performed in children range between 6% and 11%. A large part of the projected increase in CT scanning for adults will probably come from new CT-based screening programs for asymptomatic patients.

The four areas attracting the most interest are CT colonography (virtual colonoscopy ), CT lung screening for current and former smokers, CT cardiac screening, and CT whole-body screening. Quantitative Measures Various measures are used to describe the radiation dose delivered by CT scanning, the most relevant being absorbed dose, effective dose, and CT dose index (or CTDI). Autocad Blocks Of Playgrounds Surf. The absorbed dose is the energy absorbed per unit of mass and is measured in grays (Gy). One gray equals 1 joule of radiation energy absorbed per kilogram. The organ dose (or the distribution of dose in the organ) will largely determine the level of risk to that organ from the radiation.