Hounsfield scale

The Hounsfield scale /ˈhaʊnzˌfiːld/, named after Sir Godfrey Hounsfield, is a quantitative scale for describing radiodensity. It is frequently used in CT scans, where its value is also termed CT number. The Hounsfield scale /ˈhaʊnzˌfiːld/, named after Sir Godfrey Hounsfield, is a quantitative scale for describing radiodensity. It is frequently used in CT scans, where its value is also termed CT number. 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 (STP) is defined as zero Hounsfield units (HU), while the radiodensity of air at STP is defined as -1000 HU. In a voxel with average linear attenuation coefficient μ {displaystyle mu } , the corresponding HU value is therefore given by: where μ water {displaystyle mu _{ extrm {water}}} and μ air {displaystyle mu _{ extrm {air}}} are respectively the linear attenuation coefficients of water and air.