Computed ultrasound tomography in echo mode (CUTE) for imaging speed of sound using pulse-echo sonography

Patent metadata

Field	Value
Publication number	US-10271819-B2
Application number	US-201415104992-A
Country	US
Kind code	B2
Filing date	Dec 16, 2014
Priority date	Dec 16, 2013
Publication date	Apr 30, 2019
Grant date	Apr 30, 2019

Abstract

The invention relates to a method for determining and particularly imaging sound speed in an object by means of pulse-echo ultrasound, comprising the steps of: transmitting by means of an ultrasound probe ( 1 ) at least a first ultrasound pulse ( 10 ) in a first direction (φ 0 ) and a second ultrasound pulse ( 20 ) in a different second direction (φ) into an object (O) to be imaged, so that said first ultrasound pulse ( 10 ) is backscattered in said object towards said ultrasound probe in the form of first ultrasound pulse echoes ( 11 ), and so that said second ultrasound pulse ( 20 ) is backscattered in said object towards said ultrasound probe in the form of second ultrasound pulse echoes ( 21 ), detecting said backscattered first ultrasound pulse echoes ( 11 ) and said backscattered second ultrasound pulse echoes ( 21 ) with said ultrasound probe ( 1 ), reconstructing from said detected backscattered first ultrasound pulse echoes ( 11 ) a first image of first local echoes ( 5 ) and from said detected backscattered second ultrasound pulse echoes ( 21 ) a second image of second local echoes ( 7 ), wherein said images lie in an image plane spanned by said directions (φ 0 , φ), determining from said reconstructed images the respective resulting local echo phase shift Δτ(x, z, φ, φ 0 ) corresponding to the difference in echo time (t) between the respective first local echo and the corresponding second local echo relative to the case of an assumed constant sound speed, and determining the local sound speed c(x, z) in said object for at least a region of said image plane in said object from said local echo phase shift Δτ(x, z, φ, φ 0 ). Further, the invention relates to a corresponding computer program and a system.

First claim

The invention claimed is:

1. Method for determining sound speed in an object by means of ultrasound, comprising the steps of:
transmitting by means of an ultrasound probe ( 1 ) at least a first ultrasound pulse ( 10 ) in a first direction (φ 0 ) and a second ultrasound pulse ( 20 ) in a different second direction (φ) into an object (O) to be imaged, so that said first ultrasound pulse ( 10 ) is backscattered in said object towards said ultrasound probe ( 1 ) in the form of first ultrasound pulse echoes ( 11 ), and so that said second ultrasound pulse ( 20 ) is backscattered in said object towards said ultrasound probe ( 1 ) in the form of second ultrasound pulse echoes ( 21 ),
detecting said backscattered first ultrasound pulse echoes ( 11 ) and said backscattered second ultrasound pulse echoes ( 21 ) with said ultrasound probe ( 1 ),
reconstructing from said detected backscattered first ultrasound pulse echoes ( 11 ) a first image of first local echoes ( 5 ) and from said detected backscattered second ultrasound pulse echoes ( 21 ) a second image of second local echoes ( 7 ), wherein said images lie in an image plane spanned by said directions (φ 0 ,φ),
determining from said reconstructed images the respective resulting local echo phase shift Δτ(x,z,φ,φ 0 ) corresponding to the difference in echo time (t) between the respective first local echo and the corresponding second local echo compared to the case of an assumed constant sound speed in said object (O), and
determining the local sound speed c(x,z) in said object (O) for at least a region of said image plane in said object (O) from said local echo phase shift Δτ(x,z,φ,φ 0 ).

2. Method according to claim 1 , characterized in that a sound speed image is generated from the local sound speed c(x,z).

3. Method according to claim 1 , characterized in that said determining of the local sound speed c(x,z), said generating of said sound speed image from the local sound speed c(x,z), and/or said visualizing is conducted in real-time.

4. Method according to claim 1 , characterized in that the first local echoes ( 5 ) of each A-line of said reconstructed first image are modeled as first amplitude-modulated complex sinusoidal carriers, respectively, and that the second local echoes ( 7 ) of each A-line of said reconstructed second image are modeled as second amplitude-modulated complex sinusoidal carriers, respectively, wherein the respective local echo phase shift Δτ(x,z,φ,φ 0 ) is determined as the phase shift between the respective first carrier and the corresponding second carrier.

5. Method according to claim 1 , characterized in that the respective local echo phase shift Δτ(x,z,φ,φ 0 ) is determined by
calculating a first Hilbert transform of said first image of first local echoes ( 5 ) and a second Hilbert transform of said second image of second local echoes ( 7 ), respectively,
calculating a pointwise product between the first Hilbert transform and the complex conjugate of the second Hilbert transform,
calculating a convolution of the point-wise absolute magnitude of the pointwise product with a convolution kernel yielding a local average echo power,
determining a pointwise quotient between the point-wise product and its associated average local echo power,
calculating a complex local average of the point-wise quotient by calculating a convolution of the point-wise quotient with a convolution kernel, and
determining the respective local echo phase shift Δτ(x,z,φ,φ 0 ) as the argument of said complex local average of the pointwise quotient.

6. Method according to claim 1 , characterized in that the discrete Fourier Transform Δτ(k x ,k z ,φ,φ 0 ) of the local echo phase shift Δτ(x,z,φ,φ 0 ) is calculated for determining the local sound speed c(x,z).

7. Method according to claim 1 characterized in that the local sound speed c(x,z) in said object is determined from the Fourier transformed local echo phase shift Δτ(k x ,k z ,φ,φ 0 ) using the relation
σ( k x ,k z )= T inv ( k x ′,k z ′,k x ,k z ,φ,φ 0 )·Δτ( k x ′,k z ′,φ,φ 0 ),

or a relation equivalent hereto, wherein σ(k x ,k z ) is the discrete Fourier transform of the slowness σ(x,z), wherein the slowness σ(x,z) is the reciprocal of the sound speed c(x,z) minus an average slowness, and T inv is a matrix.

8. Method according to claim 7 , characterized in that said matrix T inv is an inverse matrix of the matrix
T ( k x ′,k′ z ,k x ,k z ,φ,φ 0 )= M ( k x ′,k z ′,k x ,k z ,φ)− M ( k x ′,k z ′,k x ,k z ,φ 0 ), M having the components M k′,k (φ)

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Assignees

• Univ Bern

Inventors

• Frenz Martin
• Jaeger Michael

Classifications

• G01S15/8977

  using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution · CPC title

• G01S7/52077

  with means for elimination of unwanted signals, e.g. noise or interference · CPC title

• G01S7/52071

  Multicolour displays; using colour coding; Optimising colour or information content in displays, e.g. parametric imaging · CPC title

• G01S7/52049

  using correction of medium-induced phase aberration · CPC title

• G01S7/52036

  using analysis of echo signal for target characterisation · CPC title