What is the primary method used to assess bone mineral density?

• A. Ultrasound
• B. DXA
• C. CT
• D. MRI

Answer: (B)

Measuring bone mineral density with a validated imaging test is the key idea. Dual-energy X-ray absorptiometry (DXA) provides the most accurate, reproducible BMD measurements at the sites where fracture risk matters most, such as the lumbar spine and hip. It uses two X-ray beams at different energies to separate bone from soft tissue and yields a BMD value along with T-scores and Z-scores that guide osteoporosis diagnosis and fracture risk assessment. DXA is fast, has low radiation, and is widely standardized, with clear diagnostic thresholds (for example, a T-score ≤ -2.5 defines osteoporosis).

Other modalities exist but are not the primary method. Ultrasound can estimate bone density at peripheral sites (like the heel) but lacks the comprehensive, validated diagnostic thresholds for osteoporosis. CT-based methods can quantify BMD but involve higher radiation and cost, and MRI does not measure mineral density directly.