![]() If you search PubMed on “Hounsfield units” you will get 1305 hits. However there are more sophisticated ways to use the Hounsfield units. This is probably the intended use when Hounsfield created the unit and its scale. Practical use of Hounsfield units įirst of all it is of everyday use to characterize what you see in a CT-image – “water”, air and blood are good examples of this. In the CT-image the rotating camera creates 3D-data and the corresponding unit will be a volume pixel a voxel. If you look at a computer screen “everybody” knows that there are a large number of square cells that make up the picture we see. When recreating the data from a computerized tomography you will have a large number of data for “each cell” in the 3D-image of the patient. Fluid filled spaces, for example cysts, could contain something close to water or have an attenuation corresponding to blood – of course of great importance to the physician. This makes it possible to evaluate things that do not have a specific structure – a rounded tumor could be made of fat or not – benign or malignant. Of importance is that fat is -100, muscle and blood around +40. Typical values for different elements and tissues range from -1000 to more than +1000, air versus bone. This has been the background for creating the linear Hounsfield scale where water (at STP) represents a value of 0 and air represents a value of -1000. Man is based on water and surrounded by air. It measures radiodensity and is a quantitative scale. The Hounsfield unit is a way to characterize radiation attenuation in different tissues and thus making it easier to define what a given finding may represent. It is important to realize that Hounsfield units are not based on SI-units or derived from such. CT-imaging has revolutionized medical imaging and made it possible to diagnose malignant disease in the brain and in the abdomen – regions where ordinary X-ray imaging has been of little use. The name of this unit is in honor of Sir Godfrey Hounsfield (1919-2004) – one of the pioneers of the computerized tomography (CT).
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