SUMMARY

Noninvasive viscoelasticity imaging, or “dynamic elastography”, methods have recently been developed to objectively quantify the local viscoelastic properties of soft tissues by measuring the local propagation velocity of mechanical shear vibrations (e.g. faster velocity indicates stiffer material). But the existing elastography technologies require a (potentially uncomfortable) external mechanical stimulation (e.g. vibrations probe) to induce muscle vibrations and sophisticated and expensive imaging equipments (such as MRI and ultrafast ultrasound elastography), involving complex signal processing, to record and analyze these muscle vibrations. The long-term goal of this PhD thesis is to develop a simple and low-cost alternative to existing active elastography techniques for assisting medical management and rehabilitation of patients with musculoskeletal and neuromuscular disorders (MND).

During voluntary muscular contractions, low frequency vibrations (<100 Hz) are naturally generated along the muscle as a result of the muscle fiber. The overall objective of this proposal is to develop a passive (i.e. without external source) elastography technique for low-cost and rapid, non-invasive measurements of the viscoelastic properties of human skeletal muscles using only natural muscle vibration recordings from skin-mounted sensors. This passive elastography technique uses the coherent portion of these natural vibrations propagating along the muscle between sensor pairs to estimate the local velocity (and attenuation) of muscle soft tissues and ultimately the spatial distribution of viscoelastic properties using a bio-mechanical model. The frequency, origin and directionality, mechanical interpretation, and bio-mechanical modeling of the natural muscle vibrations will be investigated, using skin-mounted accelerometer arrays, in order to determine their suitability for passive elastography. Furthermore, the accuracy of passive elastography, for estimation of non-uniform stiffening of a contracting muscle and its alterations due to the details of its condition or task, will be validated using ultrafast ultrasound elastography measurements. Elastography could facilitate the development of quantitative scales for assessing therapeutic progress (thus enhancing the ability to justify treatment) as well as portable tele-monitoring systems (e.g. using portable miniature wireless accelerometers) for personalized care of patients with MNDs.