Biomechanics and Motion Analysis

Skeletal Muscle Characterazation by Magnetic Resonanace Elastography

Project Coordinator: Qingshan Chen: — chen.qingshan@mayo.edu

Figure 58: Wave propagation through gastrocnemius

Magnetic Resonance Elastography (MRE) is a novel technique recently developed at Mayo Magnetic Resonance Research Laboratory for non-invasively measuring the stiffness of biological tissues. The technique employs standard MRI equipment with a few modifications and an electromechanical vibrator that applies vibration to the test material. This technique has been safely and successfully applied to in vivo tissues in humans, specifically to skeletal muscle. In collaboration with the magnetic Resonance Research Laboratory, MRE is applied to the study of skeletal muscle biomechanics. Skeletal muscle is of biomechanical interest since its stiffness changes reversibly and voluntarily during muscle contraction.

The stiffness modulus can be measured in multiple muscles simultaneously during a biomechanical task and these moduli are then used to calculate the tension in each muscle. MRE also has potential as a diagnostic tool inmuscle disease such as stroke, hyperthyroidism, disuse atrophy, or paralysis. MRE works by creating shear waves within tissues, which propagate away from the vibration source. The electromechanical vibrator, or “tapper”, is the wave source. The MRI scanner is sensitized to cyclic motion within the tissue so that the shear waves can be visualized. Muscle loading devices have been developed for the ankle, knee, and the neck. Material stiffness is determined from the MRE image by measuring the wavelength of the shear waves. Regional wavelength estimation method is being developed to measure the wavelength of the shear waves.

The MRE technique will be applied in vivo to provide elastographic images of abnormal muscle with known disorders. The patient groups chosen for study are each important in their own right, and furnish unique information across the spectrum of muscular disease and dysfunction. Groups to be studied include individuals with new onset of spasticity following an ischemic, hemispheric stroke, disuse atrophy as a result of immobilization, metabolic (hyperthyroid) myopathy and myofascial pain for trigger point identification.

The overall hypothesis of this work is that MRE is a novel and exciting technology that will bring benefits to both basic research and clinical care.