Table. Comparison of different technologies for measuring bone mineral density.

Test	Radiation*	Sites	Advantages	Disadvantages	Clinical use
DXA	Minimal (4 microsievert)	Hip, spine, forearm	High precision, reproducible, correlates well with fracture risk	Affected by many artefacts, including previous fractures, spinal pathology, extrinsic artefacts, obesity	Hip bone mineral density best predictor for hip fracture. Lumbar spine bone mineral density best for monitoring treatment effect
QCT	High (200 microsievert at spine, 1200 microsievert at hip)	Hip, spine	Selective measurement of trabecular and cortical bone, true volumetric bone mineral density	Less reproducible, less standardisation, fewer analysis protocols	Sensitive for monitoring vertebral bone loss and treatment effect, especially in known spinal disease or artefacts
pQCT	Minimal (3–5 microsievert)	Distal bone (usually radius, tibia)	Compact and mobile machines	Small peripheral regions only, slow changes over time	Children
HR-pQCT	Minimal (5 microsievert)	Tibia, radius	Non-invasive measurement of microarchitecture, structure and mechanical strength	Small peripheral regions only, expensive machinery	Research tool for non-invasive determination of bone structure
QUS	None	Calcaneus, radius, tibia	Portable, no ionising radiation	Not standardised, operator dependent, poor reproducibility	May be able to predict fracture risk, but conflicting evidence for monitoring while on treatment

* Daily background radiation approximately 5 microsievert, standard chest X-ray 20–60 microsievert

DXA dual energy X-ray absorptiometry

HR-pQCT high-resolution peripheral quantitative CT

pQCT peripheral quantitative CT

QCT quantitative CT

QUS ultrasonography