ULTRASOUND CHARACTERIZATION OF BONE DEMINERALIZATION

Quantitative ultrasound (QUS) assessment of bone may permit an assessm ent of bone properties currently not available by bone densitometry te chniques. To explore the effects of the quantity of bone mineral on ac oustic parameters, we carried out an in vitro study of the impact of d emineralization on attenuation of ultrasound in trabecular bone. Ten f resh cubes of trabecular bone obtained from bovine distal femurs were progressively demineralized using formic acid solution. The progressio n of demineralization was controlled by monitoring the specimen bone m ineral density (BMD) using dual x-ray absorptiometry (DXA). At five st ages of demineralization-0% (baseline), 25%, 50%, 75%, and 100% (all m ineral removed)-the US properties of the specimens were assessed (Walk er Sonix UBA 575+). The US parameters investigated were broadband ultr asound attenuation (BUA) and ultrasound attenuation in bone (UAB). Bot h DXA and QUS measurements were made along the three orthogonal axes o f each cube. Our results demonstrated significant variability in both BUA and UAB along the three principle axes of the cubes whereas BMD di d not differ in the different directions. A strong but nonlinear corre lation was found between BMD and US attenuation. A reduction in BMD to 50% of the baseline values resulted in BUA (UAB) reduction to 25% and 19%, respectively. A random effect model analysis supported a multipl icative relationship between BMD and the US parameters. US attenuation is a sensitive indicator of bone mineral changes with nonlinear depen dence on bone mineral loss. Bone collagen structure reinforced by hydr oxyapatite crystal accounts for fundamental US characteristics. Ultras ound attenuation associated with trabecular orientation is basically d ominated by the mineral spread in a collagen framework.