Bone mineral density (BMD) is defined as the amount of mineral (calcium hydroxyapatite) per unit of bone and can be used as an indirect indicator of bone strength. The bone mineral density is used to determine if osteopenia or osteoporosis are present.
Radiographic features
Bone mineral density can be measured by various methods, with DEXA being the most prevalent in modern clinical practice.
Bone mineral density measurement
single-energy x-ray absorptiometry
digital x-ray radiogrammetry
Ultrasound
calcaneal ultrasonography: determines bone mineral density and bone strength
speed of sound (SOS): measures velocity in the bone
broadband ultrasound attenuation (BUA): measures the frequency in the bone
CT
advantageous for opportunistic screening but research not advanced enough yet for implementation into clinical practice 4
HU measurements vary on anatomic site including by individual vertebra 4
scanner variability is also a significant factor with HU threshold for diagnosis of osteoporosis varying between 99 and 136 HU 4
MRI
quantitative magnetic resonance imaging: depicts changes in the trabecular structures at several sites of the peripheral skeleton
Nuclear medicine
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gamma rays (gamma decay): replaced by radiographic methods
single-energy photon absorptiometry (SPA) was superseded by the introduction of single x-ray absorptiometry; both methods measure density at peripheral sites in the skeleton (e.g. distal radius, calcaneus), but the disadvantage is that it cannot measure trabecular and cortical bone separately
dual-energy photon absorptiometry (DPA) also has been replaced by dual-energy x-ray absorptiometry (DEXA)
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