Measurement of shear waves in tissue

Abstract

The wavelength of a propagating pulse of shear wave within tissue is related to the local shear modulus and density through the speed of propagation. If the pulse does not produce standing waves, then the wavelength is a function of the tissue properties and not boundary conditions. Methods for imaging such waves using ultrasound and magnetic resonance imaging have recently been developed. The MRI method, termed Magnetic Resonance Elastography, can measure displacements in all three dimensions and is sensitive to motion of the order of 100 nanometers. The ultrasound method can measure in one plane very quickly and is sensitive to displacements of fractions of micrometers. Local wavelength of the propagating shear waves can be measured using specially modified filters. Shear modulus can then be estimated if density is known or assumed. Applications of this method reminiscent of palpation but in three dimensions and at any depth in the tissue are possibilities.