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Quantitative ultrasound parametric images of cancellous bone compared to X-ray computed tomography

Quantitative ultrasound is a radiation free technique able to assess skeletal properties that may not be reflected by other measurements like X-ray absorptiometry or quantitative computed tomography. We have previously shown that quantitative images of ultrasound velocity and attenuation is a precise method to characterize a heterogeneous medium such as the calcaneus. The present study compares the images of ultrasonic properties with the X-ray computed tomography (CT) images from 15 calcanei removed from cadavers (age ranging from 69 to 89). The values of velocity, attenuation and bone mineral density (BMD) were averaged over regions of interest (ROI) which were exactly matched for the three images. The correlation coefficient between attenuation and velocity was r=0.98, between attenuation and BMD r=0.43 and between velocity and BMD r=0.91. The observed correlation coefficients between ultrasound and QCT were highly significant (p<10 -4), but it leaves about 15% to 20% of the variability of ultrasound parameters unexplained by the BMD variation. The technique also yielded elasticity images of bone. Elasticity images were obtained by combining ultrasonic scanning measurement of the local velocity of sound in the sample with X-ray computed tomographic measurement of its local mass density. Elasticity mapping might be useful for modelling with finite elements the elastic behaviour of bone and to compute local stresses and overall deformations