Hounsfield unit

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The numerical unit assigned electronically to each pixel in a computerized tomography (CT) image, according to its X-ray density. The fixed points on the scale are arbitrarily assigned as −1000 for air and 0 for water. The CT image is viewed in a ‘window’. The range of Hounsfield units displayed (window width) and the centre point of the range of interest (window level) can be varied by the radiologist in order to observe specific tissues (see windowing). The unit was named after Sir Godfrey Hounsfield (1919–2004), who developed CT scanning in the 1950s. Symbol: HU.

Subjects: Medicine and Health.

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