Non-invasive monitoring of Achille's tendon stiffness variations in-vivo using mechanical vibrations

Abstract

A non-invasive monitoring technique of laser Doppler vibrometer (LDV) is used to find the stiffness of Achilles tendon. It is difficult for an ultrasound to collect the elastographic images of high stiffness areas such as Achilles tendon. Magnetic resonance images (MRI) technique is expensive and requires extensive training of the clinicians for elastographic image processing. This non-invasive technique needs short setup time and a simple physical structure for the data collection. A shaker is used as an excitation source, which generates waves on the tendon surface. This dynamic elastography technique measure wave velocities by an LDV. Achilles tendon is excited from 10 Hz to 1000 Hz using shaker and sensed by the LDV at four positions, which are one cm apart. Cross correlation signal processing is used for finding the time delays of the waves approaching each sensor location. It is found that as the contraction level increases, tendon stiffness increases. A comparison of average and varied stiffness values is shown in Achilles tendon. This technique may assist clinicians in characterizing muscle tone changes due to sport injuries in tendon.