Quantitative computed tomography

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 at the lumbar spine and hip.

In general, solid phantoms placed in a pad under the patient during CT image acquisition are used for calibration. These phantoms contain materials that represent a number of different equivalent bone mineral densities. Usually either calcium hydroxyapatite (CaHAP) or potassium phosphate (K₂HPO₄) are used as the reference standard.^[2]