Method and system for characterising a medium using ultrasound

Patent metadata

Field	Value
Publication number	US-12551189-B2
Application number	US-202418979787-A
Country	US
Kind code	B2
Filing date	Dec 13, 2024
Priority date	Dec 13, 2023
Publication date	Feb 17, 2026
Grant date	Feb 17, 2026

Abstract

An ultrasound characterisation method of a medium comprising the steps of generating a series of incident ultrasound waves, measuring a canonical reflection matrix defined between the input emission base and an output reception base, determining a set of responses of the medium obtained from the canonical reflection matrix, at a plurality of frequencies and for several points in a region around a reference point, determination of a frequency correction law from the responses of the medium at the various points, the frequency correction law being adapted to the reference point and being determined at frequencies, determination of the corrected responses of the medium by applying the frequency correction law to the responses of the medium around the reference point and for the plurality of frequencies.

First claim

The invention claimed is:

1 . An ultrasound characterisation method of a medium, comprising:
generating a series of incident ultrasound waves in a zone of interest of said medium, by means of an array of transducers, said series of incident ultrasound waves being an emission base; and measuring a canonical reflection matrix R ui (t) defined between the input emission base (i) and an output reception base (u), the coefficients of this canonical reflection matrix corresponding to the signals received by the transducers and induced by the ultrasound waves reflected in the medium; said method further comprising a correction process comprising: determining a set of responses R of the medium which are obtained by a focusing process for several frequencies f of the signals received from the reflected ultrasound waves and for several points of spatial position r=(x,z) of a region around a reference point of spatial position r p =(x p ,z p ) from the canonical reflection matrix R ui (t) for a sound speed model c 0 , determining a frequency correction law Φ by averaging or correlating the responses of the medium at different spatial position points (x,z) around the reference point, the frequency correction law being adapted to the reference point and being determined at frequencies f, and determining the corrected responses R′ of the medium by applying the frequency correction law Φ to the responses R of the medium around the reference point and for the plurality of frequencies f.

2 . A method according to claim 1 , further comprising:
determining an intensity I c of an echographic image point corresponding to the reference point of spatial position by combining the corrected responses at several frequencies f of that reference point.

3 . A method according to claim 1 , wherein:
the determining the set of responses R of the medium includes determining responses which are obtained by the focusing process between a first point of spatial position r in =(x in ,z) corresponding to an input virtual transducer and a second point of spatial position r out =(x out ,z) corresponding to an output virtual transducer, the first point and the second point being identical (r in =r out ), and all the responses R being recorded in a confocal reflection matrix R the coefficients of which can be written as follows R=[R(x,z,f)], the determining the frequency correction law Φ is carried out by correlating the responses of the medium at different spatial positions (x,z) around the reference point, and the coefficients of which are written as follows Φ=[ϕ(f,r p )] the determining the corrected responses R′ around the reference point is carried out by applying the frequency correction law at each frequency f, by carrying out the term product between the confocal reflection matrix R and the phase conjugate of the frequency correction law Φ; i.e. by:
R′=RºΦ*
 where all the corrected responses R′ are recorded in a corrected confocal reflection matrix R′ the coefficients of which can be written as follows R′=[R′(x,z,f)] the symbol º is the Hadamard product, such that:
R ′( x,z,f )= R ( x,z,f )Φ*( f,r p ).

4 . A method according to claim 3 , further comprising:
determining an intensity I c of an echographic image point of spatial position (x,z) by combining the corrected responses R′ of that point at a plurality of frequencies f, i.e. by:

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5 . A method according to claim 3 , wherein determining a frequency correction law includes:
constructing a correlation matrix C from the confocal reflection matrix R(z,f), and analyzing the correlation matrix C to determine the frequency correction law Q.

6 . A method according to claim 5 , wherein
the correlation matrix C is determined in the frequency domain by:
C ( f,f ′)=Σ x,z R ( x,z,f ) R *( x,z,f ′)

where R is the confocal reflection matrix, x, z are the coordinates of the points of the region around the reference point, and * is the conjugation operator.

7 . A method according to claim 5 , wherein
the correlation matrix C is determined in a base of image points of spatial position (x,z), by:
C ({ x,z},{x′,z ′})=Σ f R ( x,z,f ) R *( x′,z′,f )

where R is the confocal reflection matrix, x, z are the coordinates of the image points in the region around the reference point, and * is the conjugation operator.

8 . A method according to claim 5 , wherein:
analyzing the correlation matrix C comprises performing an eigenvalue decomposition of the correlation matrix C, and the frequency correction law Φ is the first eigenvector U 1 of the correlation matrix C.

9 . A method according to claim 5 , wherein:
analyzing the correlation matrix C comprises resolving an equation involving the correlation matrix C and the frequency correction law Φ,this equation resolution corresponding to an iterative time reversal or an iterative phase reversal.

10 . A method according to claim 3 , wherein:
determining the frequency correction law is carried out by an optimisation algorithm maximising the confocal intensity of an ultrasound image in the region around the reference point.

11 . A method according to claim 3 , wherein:
the steps of the correction processing are iterated several times, and at each iteration, the corrected confocal reflection matrix R′(z,f) obtained at the previous iteration is used instead of the confocal reflection matrix R(z,f).

12 . A method according to claim 11 , wherein:
at each iteration, the size of the region around the spatial position reference point r p is reduced.

13 . A method according to claim 3 , wherein:
determining the confocal reflection matrix R(z,f) includes compensating for the time attenuation of the signals.

14 . A method according to claim 1 , wherein:
determining the set of responses R of the medium includes determining responses which are obtained by the focusing process between a first point of spatial position r in =(x in ,z) corresponding to an input virtual transducer and a second point of spatial position r out =(x out ,z) corresponding to an output virtual transducer, the first point and the second point being located in the region at the same depth z, the transverse positions x in and x out of the first and second points forming a focused base (x) at each depth z, and all the responses R being re

Assignees

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

Inventors

• Bureau Flavien
• Giraudat Elsa
• Lambert William
• Etaix Nicolas
• Fink Mathias
• Aubry Alexandre
• Le Ber Arthur

Classifications

• G01S7/52057

  Cathode ray tube displays · CPC title

• G01N2291/105

  two or more emitters, two or more receivers · CPC title

• G01N29/221

  Arrangements for directing or focusing the acoustical waves (electronic orientation or focusing G01N29/262; sound directing or focusing G10K11/26; mechanical steering of sound transducers or their beams G10K11/35) · CPC title

• G01N29/4463

  Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering · CPC title

• G01N29/12

  by measuring frequency or resonance of acoustic waves {(measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00)} · CPC title