Measurement of the quadriceps muscle displacement and strain fields with ultrasound and Digital Image Correlation (DIC) techniques

Abstract

Objectives – In vivo characterization of muscle tissues is necessary to increase the understanding of musculoskeletal pathologies. Currently, few imaging techniques are able to characterize the in vivo mechanical properties of muscle. Thus, the purpose was to couple experimental and numerical tools to characterize the displacement and strain fields. This approach was validated on a phantom and then applied in vivo on thigh muscles.Materials and methods – An experimental compression device was developed in order to measure the displacement field from a phantom with inclusions, and from quadriceps muscle, using compressed and uncompressed ultrasound acquisitions (9 MHz). A diffuse approximation method was used to determine the optimal ZOI (Zone Of Interest) size (4, 8, 16 pixels) allowing for the realization of the DIC with a low noise and a high spatial resolution (about 100 μm). Then, the strain field was represented with a diffuse approximation radius, optimized from the theoretical noise.Results – The in vitro and in vivo displacement fields confirmed the qualitative ultrasound observations. The ZOI size was found optimal at 8 pixels. Then, the diffuse approximation radii were determined at 9 and 13 data points for the phantom and the quadriceps, respectively, providing the strain field cartographies. These cartographies validated the experimental protocol and the displacement field measurement.Conclusion – The present study revealed the feasibility of the Digital Image Correlation technique to assess the in vivo muscle mechanical behavior, and could be extended to different soft tissues.