Biomechanics and Motion Analysis

Magnetic Resonance Elastography

Principal Investigator: Kai-Nan An, Ph.D.
Project Coordinator: Frank Chen — chen.qingshan@mayo.edu

Magnetic Resonance Elastography (MRE) is a novel technique for non-invasively measuring the stiffness of biological tissues. The technique employs standard MRI equipment with a gradient-coupled vibration that causes shear waves in the test material. These shear wave are then used to calculate the material's stiffness based on the principle that a stiffer material has a longer wavelength. MRE has potential as a diagnostic tool in muscle disease such as stroke, hyperthyroidism, disuse atrophy, or paralysis.

Figure 33:     a) oblique plane through calf muscle, showing extensor digitorum longus (EDL), extensor hallucis longus (EHL), soleus (sol) and medial gastrocnemius (MG), b) line profile drawn through the MRE image of the extensor digitorum longus, c) sine wave from line profile drawn through the EDL.

A series of agarose gel phantom studies were completed to evaluate MRE. Dynamic mechanical analysis (DMA) is used to measure the dynamic shear modulus of the gel. We discovered that shear strain, strain rate, sample thickness and compressive clamping strains affecting the repeatability and accuracy of the DMA shear modulus measurement.

In addition to the phantom study, an extensive patient study is being conducted. The effect of (1) stroke, (2) disuse atrophy, (3) myofascial pain and hyperthyroidism on muscle stiffness is being investigated. This year we focused our efforts on improving data collection and analysis techniques while testing healthy, asymptomatic volunteers. An example of shear waves in an oblique plane through healthy calf muscle is shown in Figure 33.