Patent ID: 7252004

Claim:
An imaging method using shear waves for observing a diffusing viscoelastic medium containing particles that reflect ultrasound compression waves, said method comprising: a) an excitation step during which an elastic shear wave is generated in the viscoelastic medium; b) an observation step during which the propagation of the shear wave is observed simultaneously at a multitude of points in an observation field in the viscoelastic medium, this observation step comprising the following substeps: b1) causing an array of transducers that are controlled independently of one another to emit into the viscoelastic medium a succession of unfocused ultrasound compression wave shots at a rate of at least 500 shots per second; and b2) causing sound signals received from the viscoelastic medium to be detected and recorded in real time, said signals comprising the echoes generated by the unfocused ultrasound compression wave interacting with the reflecting particles in said viscoelastic medium; and c) at least one processing step during which: c1) the sound signals received successively from the viscoelastic medium during substep b2) are processed in order to determine successive propagation images of the shear wave; and c2) at least one movement parameter of the viscoelastic medium is determined at different points of the observation field; the method further comprising: during the excitation step a) the elastic shear wave is caused to be generated by causing at least one focused ultrasound wave to be emitted into the viscoelastic medium by said array of transducers, the focusing and the timing of said focused ultrasound wave, and the timing of said unfocused ultrasound wave being adapted so that at least some of said unfocused ultrasound waves penetrate into the observation field while the shear wave is propagating in the observation field, for at least some of the unfocused ultrasound wave emissions.