COMPARISON OF ULTRASOUND AND DUAL-ENERGY X-RAY ABSORPTIOMETRY MEASUREMENTS IN THE CALCANEUS

Ultrasound measurements have been proposed as a means of providing str uctural information on bone but have also been shown to correlate with density. High correlation coefficients have been obtained in vitro, b ut are lower for in vivo work. The aim of this study was to investigat e the relationship of broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness, to bone mineral density (BMD) measured in the calcaneus at a closely matched region of interest (ROI). Measureme nts were made in 55 post-menopausal and 20 young, normal women. Calcan eus BMD measurements were made using an ROI (fixed by reference to ext ernal axes) to represent the area and location of the ultrasound trans ducers and an ROI based on anatomical markers, positioned in the poste rior part of the calcaneus. BUA was significantly correlated with calc aneus BMD in the fixed ROI (r = 0.77, p < 0.0001) and the anatomical R OI (r = 0.78, p < 0.0001). Correlation of BUA with axial BMD was lower at r = 0.63, p < 0.0001 for the spine (L2-L4) and r = 0.59, p < 0.000 1 for the femoral neck. Results for SOS and stiffness were very simila r. From the calcaneus dual energy X-ray absorptiometry (DXA) scan imag es the region representing the ultrasound measurement area was found t o contain cortical bone edges in 60% of cases. In 16% of scans a small part (4.5 +/- 4.0%) of the ROI measurement area fell partially outsid e the heel. However, there was no obvious discrepancy in the ultrasoun d results in the individual cases where this occurred. The correlation between calcaneus BMD and BUA was improved from r = 0.72 to r = 0.86 when scans with a cortical edge in the measurement ROI were excluded. The values for SOS were similar. In summary, BMD of the calcaneus, whe n closely matched to the site of ultrasound measurement shows signific ant correlation with ultrasound measurements. By excluding scans in wh ich the ultrasound measurement appeared to include bone edges, correla tions of approximately r = 0.86 were obtained. However, the BMD result still does not explain all of the variance in the ultrasound results.