BiPlane ultrasound strain imaging during induced contraction of skeletal muscles

In this study, the feasibility of BiPlane strain imaging during controlled muscle contraction by means of electrical stimulation was examined. Two superficial muscles, the tibialis anterior and the biceps, were imaged using triggered BiPlane ultrasound. Raw frequency data were acquired at 100 Hz during induced muscle contraction. The responses, in terms of strain, to different electrical stimuli were assessed as well as the ability to track a tetanic response to an electrical pulse train of 10 and 20 Hz. An rf-based 2D strain algorithm was applied to the BiPlane data to measure strain in three orthogonal directions in the two simultaneously measured planes. Preliminary results in four volunteers revealed that BiPlane rf-based strain imaging in muscles during induced contraction is feasible. Vertical strains were measured between 10 and 30% as well as horizontal strains of -20 to -10%. A correlation was found between measured strain and electrical stimulus level, although the response could vary at lower excitation levels, since different (and fewer) motor units could be excited. The tetanic response in the muscle was tracked properly as well and individual contractions could be distinct at 10 Hz. In conclusion, BiPlane strain imaging in muscles can be used for semi-3D strain assessment in muscles. However, considering the out-of-plane motion in the images orthogonal to the fiber direction, full 3D strain imaging might be beneficial.