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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.
The density is measured in Hounsfield units, and score of 1 for 130–199 HU, 2 for 200–299 HU, 3 for 300–399 HU, and 4 for 400 HU and greater. This weighted score is then multiplied by the area (in square millimeters) of the coronary calcification.
Quantitative computed tomography (QCT) is a medical technique that measures bone mineral density (BMD) using a standard X-ray computed tomography (CT) scanner with a calibration standard to convert Hounsfield units (HU) of the CT image to bone mineral density values. [1] Quantitative CT scans are primarily used to evaluate bone mineral density ...
Radiolucency or hypodensity indicates greater passage (greater transradiancy) to X-ray photons [1] and is the analogue of transparency and translucency with visible light. Materials that inhibit the passage of electromagnetic radiation are called radiodense or radiopaque , while those that allow radiation to pass more freely are referred to as ...
His name is immortalised in the Hounsfield scale, a quantitative measure of radiodensity used in evaluating CT scans. The scale is defined in Hounsfield units (symbol HU), running from air at −1000 HU, through water at 0 HU, and up to dense cortical bone at +1000 HU [12] [13] and more.
[162] [163] [164] One study estimated that as many as 0.4% of cancers in the United States resulted from CT scans, and that this may have increased to as much as 1.5 to 2% based on the rate of CT use in 2007. [148] Others dispute this estimate, [165] as there is no consensus that the low levels of radiation used in CT scans cause damage. Lower ...
One barn is equal to 1.0 × 10 −28 m 2. The name derives from the folk expressions "As big as a barn," and "Couldn't hit the broad side of a barn", used by particle accelerator physicists to refer to the probability of achieving a collision between particles. For nuclear purposes, 1.0 × 10 −28 m 2 is actually rather large. [25]
distance 2 is the distance between the sternal notch and vertebrae. More recent studies show that simple chest x-rays are just as effective as CT scans for calculating the Haller index and recommend replacing CT scans with CXR to reduce radiation exposure in all but gross deformities. [3] [4] [5] A normal Haller index should be about 2.5.