Which imaging modality is used to measure bone mineral density in osteoporosis?

• A. Isotop-scintigraphy
• B. MRI
• C. X-ray osteodensitometry (DEXA)
• D. CT

Answer: (C)

Bone mineral density is quantified to diagnose osteoporosis and guide fracture risk assessment. The imaging modality used to measure BMD is dual-energy X-ray absorptiometry, or DEXA. It uses two X-ray beams at different energies to estimate mineral content in bone while adjusting for surrounding soft tissue, providing precise measurements at key sites such as the lumbar spine and hip. DEXA is the standard because it is highly accurate, has very low radiation exposure, is quick, and yields reproducible results. The results are reported as T-scores and Z-scores, with osteoporosis defined by a T-score of -2.5 or lower, osteopenia between -1.0 and -2.5, and normal BMD above -1.0. The lumbar spine and hip are prioritized because fractures here strongly predict overall fracture risk. Other imaging modalities can assess bone structure, marrow, or metabolic activity but do not reliably measure bone mineral density for osteoporosis screening and diagnosis: isotop-scintigraphy tracks bone turnover/metabolic activity, MRI visualizes marrow and soft tissues, and CT can estimate volumetric BMD but involves higher radiation and is not the standard screening test.