Method and system for ultrasonic characterization of a medium

Patent metadata

Field	Value
Publication number	US-11768181-B2
Application number	US-202117473080-A
Country	US
Kind code	B2
Filing date	Sep 13, 2021
Priority date	Sep 15, 2020
Publication date	Sep 26, 2023
Grant date	Sep 26, 2023

Abstract

Method for ultrasonic characterization of a medium, comprising generating a series of incident ultrasonic waves, generating an experimental reflection matrix R ui (t) defined between the emission basis (i) as input and a reception basis (u) as output, and determining a focused reflection matrix RFoc(r in , r out , δt) of the medium between an input virtual transducer (TV in ) calculated based on a focusing as input to the experimental reflection matrix and an output virtual transducer (TV out ) calculated based on a focusing as output from the experimental reflection matrix, the responses of the output virtual transducer (TV out ) being obtained at a time instant that is shifted by an additional delay δt relative to a time instant of the responses of the input virtual transducer (TV in ).

First claim

The invention claimed is:

1. Method for ultrasonic characterization of a medium in order to locally determine a preferred direction of anisotropy of scatterers in the medium, the method comprising:
generating a series of incident ultrasonic waves (US in ) in an area of said medium, by means of an array of transducers , said series of incident ultrasonic waves being an emission basis (i);
generating an experimental reflection matrix R ui (t) defined between the emission basis (i) as input and a reception basis (u) as output;
determining a focused reflection matrix RFoc(r in , r out , δt) which comprises responses of the medium between an input virtual transducer (TV in ) of spatial position rill and an output virtual transducer (TV out ) of spatial position r out , the responses of the output virtual transducer (TV out ) being obtained at a time instant that is shifted by an additional delay δt relative to a time instant of the responses of the input virtual transducer (TV in ),
determining a wavefront image for the input virtual transducer (TV in ) and for an additional delay interval, said wavefront image being determined as a function of the speed of sound co in the medium, and said wavefront image being determined based on:
the focused reflection matrix RFoc(r in , r out , δt) and
a ballistic propagation relation of the type δt(Δr out )=−sign(Δz out )·|Δr out |/c 0 , which makes it possible to extract values from the focused reflection matrix in order to construct the wavefront image, and where:

δt is the additional delay,
|Δr out | is the modulus of the vector between the input virtual transducer (TV in ) and the output virtual transducer (TV out ), with Δr out =r out −r in ,
Δz out is the component along a depth axis Z of the spatial position vector Δr out ; and
determining a preferred direction of the focal spot in the wavefront image by image processing said wavefront image.

2. Method according to claim 1 , wherein the image processing comprises extracting the outline of the focal spot by a threshold at a level lower than the maximum value in the wavefront image, this outline serving to determine the preferred direction of the focal spot.

3. Method according to claim 1 , wherein:
the wavefront image U(r in , Δx out , Δz out ) is converted from a reference system in Cartesian coordinates to a reference system in polar coordinates U(r in , Δs out , Δϕ out ),
the values of said wavefront image in the reference system in polar coordinates are summed, over a plurality of radial distance deviation values Δs out , to obtain an angular sensitivity function f(r in , Δϕ out ) for a plurality of angular values Δϕ out ,
the optimum angular value Δϕ max out (r in ) corresponding to the maximum of the angular sensitivity function is determined, said optimum angular value Δϕ max out (r in ) corresponding to the preferred direction of the focal spot associated with the input virtual transducer (TV in ).

4. Method according to claim 1 , wherein the preferred direction is corrected by an angle of view of the point of spatial position r in of the input virtual transducer (TV in ) as viewed from the array of transducers.

5. Method according to claim 4 , wherein the preferred direction is corrected by the formula:
γ out ( r in )=−2(Δϕ out max ( r in )−{circumflex over (θ)} out ( r in ))

where:
Δϕ out max (r in ) is the value of the preferred direction,
{circumflex over (θ)} out (r in ) is the correction of the angle of view,
γ out (r in ) is the angular anisotropy value.

6. Method according to claim 5 , wherein the correction of the angle of view is:

θ
^

out

(

r
in

)

=

1

∑

u
out
-

u
out
+

cos
⁡
(

θ
out

(

r
in

)

)

⁢

∑

u
out
-

u
out
+

θ
out

(

r
in

)

⁢

cos
⁡
(

θ
out

(

r
in

)

)

⁢

with
⁢

θ
out

(

r
in

)

=

a
⁢

tan
⁡
(

u
out

-

x
in

z
in

)

where:
u out ± (r) are the maximum and minimum values of positions of transducers in the array.

7. Method according to claim 1 , wherein:
the roles of the input virtual transducer(s) and of the output virtual transducer(s) are reversed in order to determine a preferred direction with

Assignees

• Supersonic Imagine
• Centre National De La Rech Scientifique—Cnrs
• Ecole Superieure Physique & Chimie Ind Ville De Paris

Inventors

• Lambert William
• Aubry Alexandre
• Fink Mathias
• Frappart Thomas

Classifications

• G01N29/07 Primary

  by measuring propagation velocity or propagation time of acoustic waves · CPC title

• G01N29/043

  in the interior, e.g. by shear waves · CPC title

• A61B8/15

  Transmission-tomography · CPC title

• G01N2291/0422

  Shear waves, transverse waves, horizontally polarised waves · CPC title

• A61B8/4483 Primary

  characterised by features of the ultrasound transducer · CPC title