Controlled motion strain measurement using lateral speckle tracking in Achilles tendons during healing

Ultrasound elastography imaging is being increasingly used to indicate the functional properties of musculoskeletal pathologies. Usually, this involves a real-time free-hand acquisition which has questionable consistency and does not provide a material deformation that is representative of the material function. This paper presents a novel method for acquiring quantitative ultrasound lateral strain images of in-vivo Achilles tendons in a controlled manner using a computer controlled foot articulation device and a novel 2D multiscale, multi-compression, sub-pixel precision block matching algorithm. The method has been applied to a longitudinal study of 21 patients with Achilles tendon rupture which have repeated data points taken over 24 weeks of therapy. The controlled lateral motion results are compared to the more conventional freehand axial-decompression method, and also against clinical measures. The results show that the controlled lateral motion strain images have a smaller standard deviation of average value than the freehand decompression motion (σ_lat = 0.77%, σ_comp =1.74%) and a tighter fitting to a strain improvement model which followed the same form as clinical measures of patient healing over the group (R_lat² = 0.78, R_comp² = 0.34).