Characterization of Skeletal Muscle Mechanical Properties Using Magnetic Resonance Elastography (MRE)

Principal Investigator: Kai-Nan An, Ph.D.
Project Coordinator: Qingshan Chen, M.S. — chen.qingshan@mayo.edu
Funding Source: NIH EB00812

Figure 1. Top: Shear wave propagation in MRE image (II) superimposed to a regular MRI scout image. Bottom: MRE stiffness image (II) superimposed to a regular MRI scout image. Blue region indicates higher stiffness value.

In vivo mechanical characterization of skeletal muscle, such as muscle stiffness, has clinical significance because multiple pathologies can potentially alter, or are related to, the mechanical properties of the skeletal muscle. Examples of these pathologies are hyperthyroid myopathy, myositis, stroke, myofascial pain, and disuse atrophy. Therefore, objective quantification of the muscle stiffness (either active stiffness or passive stiffness) can aid the diagnosis and/or treatment outcome evaluation of these pathologies. Magnetic resonance elastography (MRE) is a non-invasive MR phase contrast imaging technique that is capable of measuring the stiffness of in vivo tissue. MRE utilizes an oscillating motion sensitizing gradient to detect vibratory shear displacements propagated in a tissue caused by an external source of shear vibration. Once the field of shear wave propagation is established, stiffness distribution in the tissue can be reversely calculated via stiffness inversion algorithms based on the partial derivative equations of wave propagation.

Great progress has been made in MRE stiffness measurements of skeletal muscles in our laboratory over the past decade. In vivo MRE imaging on myofascial pain patients (n=4) showed a band-like stiffer region in the upper trapezius having a significantly higher stiffness (p<0.01) value than the surrounding muscle tissues, while the healthy volunteer (n=8) showed a uniformly distributed stiffness over the upper trapezius. Consistently, MRE phase images on the myofascial pain patients showed V-shaped wave fronts in the region of the palpated myofascial taut band, a characteristic feature of shear waves propagating in taut bands (Fig 1). The in vivo MRE examination in hyperthyroid myopathy patients has shown significant differences in shear stiffness of thigh muscles before and after treatment. Recent studies have started to explore the relationship between the changes in muscle stiffness and the extracellular matrix compositional and structural changes.

Publications

• Chen Q, Bensamoun SF, Basford JR, Thompson JM, An KN. Identification and Quantification of Myofascial Taut Bands with Magnetic Resonance Elastography. Arch Phys Med Rehab. 2007, 88:1658-61.
• Chen Q, Basford JR, An KN. Identification of Myofascial Taut Band Using Magnetic Resonance Elastography. Clin Biomech. 2008, 23 :623-9.
• Bensamoun SF, Ringleb SI, Littrell L, Chen Q, Brennan M, Ehman RL, An KN. Thigh muscle stiffness assessed with magnetic resonance elastography in hypothyroid patients before and after medical treatment. J Magn Reson Imaging. 2007, 26:708-13.
• Bensamoun SF, Ringleb SI, Littrell L, Chen Q, Brennan M, Ehman RL, An KN. Determination of thigh muscle stiffness using magnetic resonance elastography. J Mag Reson Imaging. 2006. 23:242-7.
• Chen Q, Ringleb SI, Manduca A, Ehman RL., An KN. Differential effects of pre-tension on shear wave propagation in elastic media with different boundary conditions as measured by magnetic resonance elastography and finite element modeling. J Biomech. 2006, 39:1428-34.
• Ringleb SI, Chen Q, Lake DS, Manduca A, Ehman RL, An KN. Quantitative shear wave magnetic resonance elastography: comparison to a dynamic shear material test. Magn Reson Med. 2005, 53:1197-201.
• Chen Q, Ringleb SI, Manduca A, Ehman RL, An KN. A finite element model for analyzing shear wave propagation observed in magnetic resonance elastography. J Biomech. 2005, 38: 2198-203.