Patent ID: 6770033
Filing Date: 2004-08-03
Classification: A61B,G01N,G01S

Abstract:
A method of imaging using shear waves to observe a diffusing viscoelastic medium which contains particles reflecting ultrasonic compression waves, in which method an elastic shear wave is generated in the viscoelastic medium and the displacement of the viscoelastic medium subjected to said shear wave is observed by means of at least one ultrasonic compression wave,wherein the shear wave is generated by applying to the viscoelastic medium an excitation having the form of a low-frequency pulse which exhibits a central frequency f of between 20 and 5000 Hz, this low-frequency pulse exhibiting a duration of between 1/2f and 20/f, wherein said method comprises a propagation observation step in the course of which the propagation of the shear wave is observed simultaneously at a multitude of points in the observed medium, these points forming a substantially continuous observation field extending at least along a first axis, this shear wave propagation observation step consisting in: emitting into the observed medium a succession of at least 10 shots of ultrasonic compression waves at a rate of between 100 and 100 000 shots per second, detecting and recording in real time the echoes generated by the reflecting particles of the viscoelastic medium at each ultrasonic wave shot, these echoes corresponding to successive images of the observed medium, and wherein said method furthermore comprises a subsequent image processing step in the course of which the images thus obtained are processed at a later time at least by cross-correlation between successive images, so as to determine at each point of the observation field a motion parameter chosen between the displacement and the strain of the viscoelastic medium, in such a way as to thus obtain a succession of images showing the evolution of the motion parameter of the viscoelastic medium under the effect of the propagation of the shear wave.