Analysis of wave patterns in MR elastography of skeletal muscle using coupled harmonic oscillator simulations

The ability to study muscle elasticity in vivo would be of great clinical interest. Magnetic resonance elastography (MRE) has the potential to quantify noninvasively the distribution of the shear modulus in muscle tissue. Elasticity information may be derived by extracting frequencies from the wave patterns of phase-contrast MRE images. In a new approach, MRE wave patterns were reconstructed using 3D coupled harmonic oscillator calculations (CHO). To analyze in vivo MRE measurements of the biceps brachii of healthy volunteers, different anisotropic fibrous structures for the couplings between the muscle elements have to be assumed. V-shaped wave patterns as observed when excitation was applied on the tendon were reproduced by a model, where in a central band of stiff fascicles wave propagation was about twice as fast as that in surrounding tissue. Planar waves were observed for excitation near the muscle surface. They could be reconstructed by assuming a simultaneous wave excitation of all muscle fibers, where fibers along the main muscle axis were coupled more strongly than those perpendicular to the axis. The results show that CHO calculations provide a fast and reliable method for incorporating anatomical information of the investigated tissue in the reconstruction of complex wave patterns.