Acoustic and ultrasonic tissue characterization--assessment of osteoporosis

Osteoporosis, often termed the 'silent epidemic', has been defined as 'a decrease in bone mass and architectural deterioration of bone tissue, leading to enhanced bone fragility and consequent increase in fracture risk'. In the United Kingdom alone, the annual health costs are in excess of 750 million Pounds, with 60,000 patients suffering a hip fracture each year. A quarter of these will die within 12 months of their fracture, half of the remainder will never regain independent living. The established procedure for assessing the risk of osteoporotic fracture is via bone mineral density (BMD) assessment using dual-energy X-ray absorptiometry (DXA). However, DXA is an expensive technique and is not widely available. Within the past 15 years, ultrasound assessment of bone has rapidly advanced in scientific understanding, technical development and clinical utility. Measurements of cancellous bone (particularly at the calcaneus) are generally performed in preference to those of cortical bone (tibial cortex). There are currently 15 commercial systems available and over 3500 systems are in use world-wide. The low cost and portability offered by ultrasound systems should enable an integrated community-based screening programme to be established in the near future. Ultrasound measurements of bone are generally obtained using transmission rather than pulse-echo techniques owing to its highly attenuating nature. Ultrasound velocity and attenuation measurements are utilized. For velocity, there are well-defined fundamental relationships describing the dependence upon the elasticity and density of bone.