High-resolution monitoring of the velocity of ultrasound in contracted and relaxed human muscle

A differential detection scheme has been developed to monitor the variations of the velocity of longitudinal polarised ultrasound waves travelling in contracted and relaxed human muscle, compensating for variations of the path length by referencing to a frame. This allows to monitor in vivo changes of the velocity of ultrasound travelling in human muscle with so far not reported resolution. To achieve this, the monitored muscle is placed into a rigid enclosure to minimise deformations under contraction. Detected is a maximum increase in the speed of ultrasound from 1 to 3.7 MHz of only (0.6 ± 0.05)% under contraction. Results are compared to modelling based on well-established rather elementary assumptions for idealised liquids and soft mater and to features derived from related published observations and assumptions. Knowledge on variations of the velocity of ultrasonic waves as demonstrated here is important for image reconstruction in ultrasonic imaging and for modelling of the mechanical properties of muscles, since Young's modulus and the shear modulus, both determining furthermore Poisson's number, representing together the mechanical properties of homogeneous matter can all be derived from the measured data.