Directional Filtering for Multiple-Driver Magnetic Resonance Elastography Data

D. S. Lake, A. Manduca, Y. Mariappan, R. L. Ehman Mayo Clinic College of Medicine, Rochester, MN, United States Introduction Magnetic resonance elastography (MRE) is a phase contrast based MRI imaging technique that can directly visualize and quantitatively measure propagating acoustic strain waves in tissue-like materials subjected to harmonic mechanical excitation [1]. The data acquired allows the calculation of local quantitative values of shear modulus and the generation of images that depict tissue elasticity or stiffness. The shear waves are typically produced by an electromechanical, pneumatic or piezoelectric driver, applied to the surface of the object. In some applications, adequate displacement may not be present in regions of an object due to attenuation and shadowing effects. It has been shown that excitation with multiple, phased array drivers can provide more uniform illumination of an object [2]. However, the wave field from such a driving system can be very complex, with interference patterns yielding areas of low wave amplitude and hence low SNR. A spatio-temporal directional filter can in principle separate interfering waves traveling in different directions so they can be processed separately [3]. We investigate the effect of such filtering on multiple driver MRE data sets and on stiffness results derived from these with three different inversion techniques.