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The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement into one in which the radiodensity of distilled water at standard pressure and temperature is defined as 0 Hounsfield units (HU), while the radiodensity of air at STP is defined as −1000 HU.
This makes CT scan the most appropriate term, which is used by radiologists in common vernacular as well as in textbooks and scientific papers. [218] [219] [220] In Medical Subject Headings (MeSH), computed axial tomography was used from 1977 to 1979, but the current indexing explicitly includes X-ray in the title. [221]
On 1 October 1971, CT scanning was introduced into medical practice with a successful scan on a cerebral cyst patient at Atkinson Morley Hospital in Wimbledon, London, United Kingdom. [16] In 1975, Hounsfield built a whole-body scanner. The principles of computed tomography developed by Hounsfield remain in use today (2022).
On the Hounsfield scale, distilled water has a value of 0 Hounsfield units (HU), while air is specified as -1000 HU. In modern medicine, radiodense substances are those that will not allow X-rays or similar radiation to pass.
Contrast CT of a patient with brain metastases from breast cancer, before (left) and after (right) injection of iodinated contrast.. Iodinated contrast is a form of water-soluble, intravenous radiocontrast agent containing iodine, which enhances the visibility of vascular structures and organs during radiographic procedures.
A V/Q scan may still be recommended when a lower radiation dose is required. [4] On CTPA, acute emboli have been found at radiodensities ranging between about 5 and 65 Hounsfield units (HU), while chronic emboli have ranged between about 30 and 150. [5]
In medicine, the dense artery sign or hyperdense artery sign is an increased radiodensity of an artery as seen on computer tomography (CT) scans, and is a radiologic sign of early ischemic stroke. [1] In earlier studies of medical imaging in patients with strokes, it was the earliest sign of ischemic stroke in a significant minority of cases. [2]
Blood plasma aldosterone concentration and plasma renin activity, if hypertension is present; On CT scan, benign adenomas typically are of low radiodensity (due to fat content). A radiodensity equal to or below 10 Hounsfield units (HU) is considered diagnostic of an adenoma. [7]