DEXA

DEXA, short for dual-energy X-ray absorptiometry, is a medical imaging technique used to measure bone mineral density (BMD) and, in some devices, body composition. It operates by emitting two X-ray beams at different energy levels and analyzing their absorption by bone and soft tissue to estimate mineral content. The scan is quick and involves a low dose of ionizing radiation.

Most commonly, DEXA assesses BMD at the lumbar spine and hip, with additional regions such as the forearm or whole body being measured in certain cases. Results are reported as BMD values in g/cm^2 and interpreted using T-scores and Z-scores. The T-score compares an individual’s BMD with that of a healthy young adult of the same sex, while the Z-score compares with an age-, sex-, and size-matched reference population. Categories defined for diagnosis typically include normal, osteopenia, and osteoporosis, with severe osteoporosis indicated by fragility fractures in addition to a low T-score.

Applications include diagnosing osteoporosis and osteopenia, assessing fracture risk (often in conjunction with clinical risk assessment tools), and monitoring response to treatment. DEXA is also used in research and clinical settings to estimate body composition, including fat mass and lean mass, and regional fat distribution.

Safety and limitations: DEXA uses a low level of radiation, typically a few microSieverts per scan, and is generally considered safe for most adults; pregnancy is a precaution, and procedures are usually deferred in pregnant individuals. Limitations include potential inaccuracies from degenerative spine changes, osteoarthritis, aortic calcifications, obesity, or scoliosis. BMD is one measure of fracture risk, which also depends on other factors; results should be interpreted within the broader clinical context.