n. (in radiology) the conversion of an *analogue image to a *digital image. The image is broken down to pixels and numerical values assigned to each pixel for its position and to describe its shade on the *grey scale. This allows storage, electronic manipulation, and transfer via computer links of any images, including radiographs or CT, MRI, or ultrasound scans.
(in radiology) a scale representing the possible gradient of densities from black to white for each *pixel in an image. In an *analogue image this gradient is smooth. A *digital image has many discrete steps. The more steps allowed, the closer to representing the true analogue image it comes, although more steps require more computer memory. Images can be manipulated by *windowing. This concept is particularly valuable in *computerized tomography. See Hounsfield unit; digitization.... grey scale
(helical CT scanning) a development of conventional *computerized tomography (CT) scanning in which the X-ray tube rotates continuously around the patient as he or she passes through the scanner. This allows the acquisition of images throughout a specified volume of tissue much more quickly. Since these images are digitally acquired (see digitization), *post-processing can produce images in numerous planes, without further exposure of the patient to ionizing radiation. See also multidetector computerized tomography.... spiral ct scanning
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