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A CT scan, also called X-ray computed tomography (X-ray CT) or computerized axial tomography scan (CAT scan),〔http://www.mayoclinic.org/tests-procedures/ct-scan/basics/definition/prc-20014610〕 makes use of computer-processed combinations of many X-ray images taken from different angles to produce cross-sectional (tomographic) images (virtual 'slices') of specific areas of a scanned object, allowing the user to see inside the object without cutting. Digital geometry processing is used to generate a three-dimensional image of the inside of the object from a large series of two-dimensional radiographic images taken around a single axis of rotation.〔Herman, G. T., Fundamentals of computerized tomography: Image reconstruction from projection, 2nd edition, Springer, 2009〕 Medical imaging is the most common application of X-ray CT. Its cross-sectional images are used for diagnostic and therapeutic purposes in various medical disciplines.〔(【引用サイトリンク】title=computed tomography – Definition from the Merriam-Webster Online Dictionary )〕 The rest of this article discusses medical-imaging X-ray CT; industrial applications of X-ray CT are discussed at ''industrial computed tomography scanning''. As X-ray CT is the most common form of CT in medicine and various other contexts, the term computed tomography alone (or CT) is often used to refer to X-ray CT, although other types exist (such as positron emission tomography () and single-photon emission computed tomography ()). Older and less preferred terms that also refer to X-ray CT are computed axial tomography (CAT scan) and computer-aided/assisted tomography. X-ray CT is a form of radiography, although the word "radiography" used alone usually refers, by wide convention, to non-tomographic radiography. CT produces a volume of data that can be manipulated in order to demonstrate various bodily structures based on their ability to block the X-ray beam. Although, historically, the images generated were in the axial or transverse plane, perpendicular to the long axis of the body, modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures. Although most common in medicine, CT is also used in other fields, such as nondestructive materials testing. Another example is archaeological uses such as imaging the contents of sarcophagi. Individuals responsible for performing CT exams are called radiographers or radiologic technologists〔(【引用サイトリンク】title=Patient Page | ARRT – The American Registry of Radiologic Technologists )〕〔(【引用サイトリンク】 title=Individual State Licensure Information )〕 Usage of CT has increased dramatically over the last two decades in many countries. An estimated 72 million scans were performed in the United States in 2007. One study estimated that as many as 0.4% of current cancers in the United States are due to CTs performed in the past and that this may increase to as high as 1.5 to 2% with 2007 rates of CT usage; however, this estimate is disputed, as there is not a consensus about the existence of damage from low levels of radiation. Kidney problems may occasionally occur following intravenous contrast agents used in some types of studies.〔 ==Medical use== Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography. It has more recently been used for preventive medicine or screening for disease, for example CT colonography for people with a high risk of colon cancer, or full-motion heart scans for people with high risk of heart disease. A number of institutions offer full-body scans for the general population although this practice goes against the advice and official position of many professional organizations in the field.〔(CT Screening )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CT scan」の詳細全文を読む スポンサード リンク
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