8C-4 Active and Passive Muscle Properties Assessed by Ultrasound Techniques

The non invasive and in vivo assessment of the active and passive properties of the musculoskeletal system remains today a great challenge for the understanding of muscular diseases. In a previous paper, we showed that the transient contraction of a muscle fiber bundle triggered by electrostimulation can be followed in space and time by an ultrafast ultrasound system. On the one hand, this experiment is generalized to measure the three dimensional (3D) velocity fields allowing a much easier localization of the contracting fibers bundle. On the other hand, the supersonic shear imaging technique is applied to assess viscoelastic properties of the biceps brachii in different conditions. By combining in vivo imaging of both passive and active muscle activity, this study aims to provide new potential ultrasonic tools for muscle diseases diagnosis and monitoring. In order to image the contraction, which is a very quick phenomenon, an ultrasound scanner able to take up to 5000 frames/s was used. Tissue velocities were obtained from conventional speckle tracking techniques. The probe, positioned perpendicularly to the arm in a water tank, was moved with a linear motor. For each position, the imaging system was set to trigger an electrostimulation firing the contraction. A second experiment for the assessment of passive muscle elastic properties in different positions of the arm and contraction levels is then performed using the same probe in the supersonic shear imaging (SSI) mode. Generated by the radiation force induced by a focused ultrasound beam, shear waves propagate in the medium and are imaged by an ultrafast ultrasound scanner allowing the reconstruction of viscoelastic properties. The localization of the contracting fibers bundle and the resolution of its main temporal and spatial behavior are demonstrated. Paving the way to a clinical protocol on muscle diseases, viscoelastic parameters are measured in different conditions and reproducibility is discussed. These two complementary ultrasound techniques offer new perspectives for muscle diagnosis both as an active contractile tissue and as a passive tissue.