MAGNETIC-RESONANCE-IMAGING OF TRANSVERSE ACOUSTIC STRAIN WAVES

We describe a phase contrast based MRI technique with high sensitivity to cyclic displacement that is capable of quantitatively imaging acou stic strain waves in tissue-like materials. A formalism for considerin g gradient waveforms as basis functions to measure arbitrary cyclic mo tion waveforms is introduced. Experiments with tissue-like agarose gel phantoms show that it is possible to measure small cyclic displacemen ts at a submicron level by an appropriate choice of the applied gradie nt basis function and to use this capability to observe the spatial an d temporal pattern of displacements caused by acoustic strain waves. T he propagation characteristics of strain waves are determined by the m echanical properties of the media. It is therefore possible to use thi s technique to noninvasively estimate material properties such as elas tic modulus.