absorptiometry

Absorptiometry is a set of techniques for determining the amount of a substance by measuring the absorption of radiation or light as it passes through a sample. The basic principle relies on the attenuation of an incident beam according to Beer-Lambert law, with the degree of absorption related to concentration, path length, and the absorbing properties of the material. It is used in clinical, biochemical, and industrial settings to quantify mineral content, chemical composition, or tissue characteristics.

In clinical medicine, absorptiometry is most commonly associated with bone densitometry. Early methods included single-energy absorptiometry and radiographic absorptiometry, while modern practice mostly uses dual-energy X-ray absorptiometry (DEXA or DXA) to estimate bone mineral density. DEXA uses two X-ray energies to separate bone from soft tissue, enabling measurement of mineral content per unit area and assessment of osteoporosis risk and fracture likelihood. Additional forms, such as single-photon absorptiometry, have historical importance.

Outside bone assessment, absorptiometry is used to measure concentrations in liquids or tissues by optical or gamma-ray methods. Optical absorptiometry or photometry relies on light absorption to quantify solutes in solutions. Neutron or gamma-ray absorptiometry has been used in material analysis and in some research settings to determine elemental composition or to study body composition.

Limitations include sensitivity to tissue thickness and composition, calibration requirements, and device-specific variations. Results often depend on standardized calibration with phantoms and reference data. While highly informative in bone health, absorptiometry measurements should be interpreted in context with clinical risk factors and other imaging findings.