Hounsfieldasteikolla

The Hounsfieldasteikolla, known in English as the Hounsfield scale, is a quantitative measurement system used in computed tomography (CT) to express the radiodensity of tissues relative to water. Radiodensity is measured in Hounsfield units (HU). Water is defined as 0 HU, air approximately –1000 HU, and dense bone can reach values of +1000 HU or higher. The scale is centered on the attenuation coefficient of water at a given energy level, typically 70 keV for diagnostic CT.

The scale was introduced by Sir Sir Godfrey Hounsfield, one of the pioneers of computed tomography, in 1974. It provided a standardized way to compare CT images across different machines and patients, which was crucial for diagnostic accuracy and for quantitative imaging research. The Hounsfieldasteikolla allows clinicians to differentiate between types of tissues and pathological findings—for example, fat has negative HU values (–100 to –50), soft tissue such as muscle is around +30 to +40 HU, and calcifications or bone can exceed +1000 HU.

In clinical practice the scale is used for lesion detection, assessing tumor density, guiding biopsy, and monitoring treatment response. It also underpins automatic image segmentation algorithms in radiology informatics. Variations in CT scanner calibration or patient positioning can cause minor shifts in HU values, which radiologists account for when interpreting scans. The Hounsfieldasteikolla remains a foundational concept in medical imaging, enabling consistent, reproducible, and quantitative assessment of tissue characteristics.