Method and system for ultrasonic characterisation of a medium

A method for ultrasonic characterisation of a medium comprising:

• a step of generating a series of incident ultrasonic waves (USin) in a region of said medium, by means of an array (10) of transducers (11), said series of incident ultrasonic waves forming a transmission basis (i);
• and
• a step of generating an experimental reflection matrix Rui(t) defined between the transmission basis (i) at the input and a reception basis (u) at the output, the coefficients of this matrix corresponding to the signals received by the transducers induced by the reflected ultrasonic waves;
• a step of determining a de-scanned reflection matrix R′,
• which comprises, for a set of points of the medium of abscissa x and echo time t,
• responses of the medium calculated by beamforming according to a sound speed model c0 from the experimental reflection matrix Rui(t), between an input virtual transducer of spatial position rin=(x, zt) and an output virtual transducer of spatial position rout=(x+Δx, zt), both virtual transducers being at the same depth zt, zt being the depth of the isochronous volume expected for the sound speed c0, the isochronous volume being the set of points of the medium contributing to the signals received at time t,
• the responses of the de-scanned reflection matrix R′ being determined for a set of lateral offset values Δx including at least Δx=0 and for a set of sound speed models c0,
• said de-scanned reflection matrix being formed such that each row corresponds to an element of a pair {Δx, c0} which corresponds to a focal spot image, and each column corresponds to an element of a pair {x, t}, which is written as:
• R
• ′
• =
• [
• R
• ′
• (
• {
• Δ
• ⁢
• x
• ,
• c
• 0
• }
• ,
• {
• x
• ,
• t
• }
• )
• ]
• ,
• and
• an extraction step in which, from each focal spot image, an optimal lateral offset Δxopt and an optimal sound speed model copt, close to the maximum in said focal spot image, are determined.