Diffraction tomography for sound speed estimation and aberration correction in medical ultrasound pulse-echo imaging based on propagation velocity analysis

Abstract

An improved system for medical ultrasound pulse-echo imaging based on velocity of propagation analysis is disclosed, which uses diffraction tomography for sound speed estimation and aberration correction and includes a transmit subsystem, a data acquisition subsystem, an ultrasound probe, a signal processing component based on wave equation velocity of propagation analysis (WEMVA) that provides reflectivity images and sound speed maps, and an output device configured to receive the reflectivity images and sound speed maps.

Description

[Technical Field]

[0001] Cross-reference to related patent applications This application claims priority to U.S. Provisional Patent Application No. 63 / 419,040, filed October 25, 2022, by Ali et al., entitled "Diffraction Tomography For Sound Speed ​​Estimation And Aberration Correction In Medical Pulse-Echo Ultrasound Imaging Based On Migration Velocity Analysis," the disclosure of which is incorporated herein by reference in its entirety to the extent permitted by national or local law.

[0002] The present invention relates to diffraction tomography, and more particularly to diffraction tomography for sound speed estimation and aberration correction in ultrasonic pulse-echo medical imaging based on propagation velocity analysis. [Background technology]

[0003] Distributed aberration correction in medical pulse-echo ultrasound relies on sound speed estimation, which is currently limited to methods using estimated time-of-flight of light rays. In heterogeneous acoustic media, such as the human body, encountered during medical pulse-echo ultrasound imaging, the ability to estimate the true speed of sound is critical for optimizing aberration convergence or correction in ultrasound images. Sound speed estimation in ultrasound transmission tomography is often performed using waveform inversion, a form of diffraction tomography, in which the error between measured and simulated channel data is used to estimate the sound speed. However, because sound speed estimation in ultrasound pulse-echo ultrasound relies on ultrasound reflection rather than transmission through tissue, methods using estimated time-of-flight of light rays have been predominant. Unfortunately, ray-based techniques are often unreliable in vivo, where simple time-of-flight models cannot account for nonuniform backscattering and wavefront splitting. Wave equation velocity analysis, a form of diffraction tomography that uses the discrepancy between reflections imaged at different angles to estimate the speed of sound, has been shown to overcome the limitations of optical tomography in seismology. However, such techniques have not been refined, developed, or applied to medical pulse-echo ultrasound, particularly handheld ultrasound. Improving current speed-of-sound estimation could dramatically improve image quality. Therefore, there is a need for ultrasound imaging systems with improved speed-of-sound estimation and aberration correction. Summary of the Invention [Means for solving the problem]

[0004] In accordance with the present invention, an improved system for diagnostic ultrasound imaging is provided, the system including an ultrasound system having a transmit subsystem and a data acquisition subsystem, an ultrasound probe operatively connected to the ultrasound system, a signal processing component based on wave equation migration velocity analysis (WEMVA) that provides reflectivity images and sound speed maps, and an output device configured to receive the reflectivity images and sound speed maps.

[0005] In one embodiment of the present invention, the Wave Equation Velocity Analysis (WEMVA) based signal processing component comprises a shot profile migration algorithm, a Wave Equation Velocity Analysis (WEMVA) algorithm, and a sound speed map output from the Wave Equation Velocity Analysis (WEMVA) algorithm and input to the shot profile migration algorithm.

[0006] In one embodiment of the present invention, the Wave Equation Velocity Analysis (WEMVA) based signal processing component further comprises a coherent combining algorithm configured to receive the reconstructed image from the shot profile migration algorithm and generate a reflectance image.

[0007] In one embodiment of the present invention, the Wave Equation Velocity Analysis (WEMVA) uses rays.

[0008] In one embodiment of the present invention, the output device may be a display device, a digital storage device, or a printer.

[0009] In one embodiment of the present invention, the improved system for diagnostic ultrasound imaging further comprises a network interface operatively connected to the output device.

[0010] In one embodiment of the invention, the Wave Equation Velocity Analysis (WEMVA) based signal processing component is configured to receive and process received data and transmitted metadata from the ultrasound system.

[0011] In one embodiment of the present invention, a wave equation velocity analysis (WEMVA) based signal processing system is disclosed, the system comprising a shot profile migration algorithm, a wave equation velocity analysis (WEMVA) algorithm, and a sound speed map output from the wave equation velocity analysis (WEMVA) algorithm and input to the shot profile migration algorithm.

[0012] In one embodiment of the present invention, the Wave Equation Velocity Analysis (WEMVA) based signal processing system further comprises a coherent synthesis algorithm configured to receive the reconstructed image from the shot profile migration algorithm and generate a reflectance image.

[0013] In one embodiment of the present invention, the Wave Equation Velocity Analysis (WEMVA) based signal processing system uses light rays.

[0014] A method for iterative image refinement and tissue characterization by sound speed is disclosed, the method comprising the steps of acquiring medical ultrasound pulse-echo data from an ultrasound data acquisition system, applying a shot profile migration algorithm to reconstruct an image from the acquired data, applying a wave equation velocity analysis (WEMVA) algorithm to the reconstructed image to update a sound speed map, and providing the updated sound speed map data to the shot profile migration algorithm.

[0015] In one embodiment of the invention, the method further comprises providing the updated sound speed map to an output device.

[0016] In one embodiment of the invention, the method further comprises providing a reconstructed image from the shot profile migration algorithm to a coherent combining algorithm, and generating a reflectance image from the reconstructed image provided to the shot profile migration algorithm.

[0017] In one embodiment of the invention, the method further comprises providing the reflectance image to an output device.

[0018] In one embodiment of the invention, the method further comprises providing the updated sound speed map and the reflectance image to an output device.

[0019] In one embodiment of the invention, the output device is connected to a network interface.

[0020] In one embodiment of the present invention, the output device may be a display device, a digital storage device, or a printer.

[0021] In one embodiment of the invention, the medical ultrasound pulse-echo data comprises received data and transmitted metadata.

[0022] In one embodiment of the invention, the method further comprises providing the updated sound speed map and the reflectivity image to a network.

[0023] In one embodiment of the present invention, the Wave Equation Velocity Analysis (WEMVA) algorithm uses rays.

[0024] The foregoing has been provided by way of introduction and is not intended to limit the scope of the invention as described by this specification and the accompanying drawings. [Brief explanation of the drawings]

[0025] The present invention is described with reference to the following drawings, in which like numerals refer to like elements. [Figure 1] FIG. 1 shows a block diagram of an improved system for diagnostic ultrasound imaging, according to one embodiment of the present invention. [Figure 2] FIG. 2 is a flow diagram illustrating the method of the present invention. [Figure 3] FIG. 3 is a flow diagram illustrating a method for iterative image refinement and tissue characterization by speed of sound, according to one embodiment of the present invention. [Figure 4] FIG. 4 illustrates the angular spectrum method in polar coordinates for a curvilinear array, according to one embodiment of the present invention. [Figure 5] FIG. 5 illustrates ultrasound pulse-echo imaging based on the time-domain cross-correlation of transmitted and received wave fields. [Figure 6] Figure 6 shows the application of sound speed estimation and phase aberration correction based on wave equation velocity analysis (WEMVA) to the reconstructed image. [Figure 7] FIG. 7 is a schematic diagram of the time of flight from the transmitter to the image point and back to the receiver. [Figure 8] FIG. 8 shows the delay gradient of the pulse-echo reconstruction of the target point. [Figure 9] Figures 9 and 10 show two different cases of simulated abdominal imaging before and after aberration correction. [Figure 10] Figures 9 and 10 show two different cases of simulated abdominal imaging before and after aberration correction.

[0026] While the present invention will be described in connection with preferred embodiments, it should be understood that it is not intended to limit the invention to such embodiments. Rather, the intention is to cover all alternatives, modifications, and equivalents that may be included within the spirit and scope of the invention as defined by the specification, drawings, and appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0027] Phase aberration is one of the major causes of image degradation in handheld B-mode ultrasound imaging. Nonuniform sound speed induces tissue-dependent delay and diffraction effects that are not accounted for in conventional beamforming, resulting in phase aberrations in images. Therefore, in this invention, we use the Fourier split-step angular spectrum method to simulate the pressure field in a spatially variable sound speed medium. A seismic imaging technique known as shot-profile migration is then used to generate B-mode ultrasound images. Our split-step angular spectrum method can be implemented for either linear or curvilinear arrays.

[0028] In shot profile migration, ultrasound images are reconstructed by correlating the transmitted signal with the counter-propagating received signal. Shot profile migration is parameterized by the sound speed in the medium via the angular spectrum method using split-step Fourier techniques, so that the image reconstructed by shot profile migration is optimized with respect to the sound speed, allowing for simultaneous estimation of the sound speed profile in the medium and correction of aberrations in the image. This technique represents a form of diffraction tomography known in seismic imaging as wave equation migration velocity analysis (WEMVA).

[0029] For a more complete understanding of the present invention and the various embodiments described and contemplated herein, reference is now made to the following drawings and description of the drawings.

[0030] FIG. 1 shows a block diagram of an improved system for diagnostic ultrasound imaging according to one embodiment of the present invention. An ultrasound probe 101 is connected to an ultrasound system 103. The ultrasound system includes a transmit subsystem 105 that provides acoustic waves and a data acquisition subsystem 107 that receives reflected acoustic waves. The data acquisition subsystem 107 includes a processor, memory, and access to computer-readable media. The transmit subsystem also includes a processor, memory, and access to computer-readable media. The ultrasound system 103 provides both received data 109 and transmitted metadata 111 to a Wave Equation Velocity Analysis (WEMVA) signal processing component 113. The Wave Equation Velocity Analysis (WEMVA) signal processing component includes software (the mathematical details of which are described herein below), the output of which includes a reflectivity image 115 that is provided to a display device for visual inspection, another computer or data storage device, a printer, a network interface, etc. The Wave Equation Velocity Analysis (WEMVA) signal processing component 113 also includes a processor, memory, and has access to computer-readable media to provide the reflectance images 115 and sound speed map 117 to an output device such as a display device 119, digital storage device, printer, etc. for interpretation by a medical professional. The display device 119 can also provide the reflectance images 115 and sound speed map 117 to a network, computer program, database, etc. In some embodiments of the present invention, the reflectance images 115 and sound speed map 117 are provided to downstream systems for further processing, analysis, etc.

[0031] The Wave Equation Velocity Analysis (WEMVA) based signal processing component 113 includes a processor, memory, and access to a computer-readable medium, and further includes a shot profile migration algorithm, a Wave Equation Velocity Analysis (WEMVA) algorithm, and a sound speed map output from the Wave Equation Velocity Analysis (WEMVA) algorithm and input to the shot profile migration algorithm.

[0032] In some embodiments, the wave equation propagation velocity analysis based signal processing component further comprises a coherent combining algorithm configured to receive the reconstructed image from the shot profile migration algorithm and generate a reflectance image.

[0033] In some embodiments, a signal processing component based on wave equation velocity of propagation analysis is configured to receive and process received data and transmitted metadata from the ultrasound system.

[0034] 2 is a flow diagram illustrating the method of the present invention. In step 201, a reflectivity image based on a sound speed profile is created using shot profile migration. Next, in step 205, the reconstructed image 203 is sent to a wave equation propagation velocity analysis (WEMVA), which updates the sound speed map 207 and provides an output of the sound speed map 207. The reconstructed image 203 is also sent to a coherent synthesis step 209, which uses the coherent synthesis step 209 to create a reflectivity image 211 and provide an associated output 215. The created and updated sound speed map 207 is then used as the basis for further shot profile migration steps 201.

[0035] 3 is a flow diagram illustrating a method for iterative image refinement and tissue characterization by speed of sound according to one embodiment of the present invention. The method described is executed on a computer comprising a processor, a memory, and having access to a computer-readable medium.

[0036] The method includes acquiring medical ultrasound pulse-echo data from an ultrasound data acquisition system in step 301 (see FIG. 3 ), applying a shot profile migration algorithm to reconstruct an image from the acquired data in step 303, applying a wave equation velocity analysis (WEMVA) algorithm to the reconstructed image in step 305 to update a sound speed map in step 307, providing updated sound speed map data to the shot profile migration algorithm in step 309, and creating or updating sound speed map and reflectivity image outputs in step 311.

[0037] The method may also include providing the updated sound speed map to an output device.

[0038] The method may also include providing images reconstructed by the shot profile migration algorithm to a coherent combining algorithm, and generating a reflectance image from the reconstructed images provided to the shot profile migration algorithm.

[0039] The method may also include providing the reflectance image to an output device.

[0040] The method may also include providing the updated sound speed map and the reflectivity image to an output device.

[0041] The output device may be a display device, a digital storage device, a printer, a network or a network interface, or the like.

[0042] The medical ultrasound pulse-echo data includes received data and transmitted metadata.

[0043] The method may also include providing the updated sound speed map and the reflectivity image to a network.

[0044] Various methods of the present invention are described below.

[0045] A. Angular Spectrum Method Using Split-Step Fourier Method for Linear Arrays The ultrasonic wave field p(x,z,f) as a function of position (x,z) and frequency f can be propagated from depth z to z+Δz using the angular spectrum method with split-step Fourier analysis.

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[0053] B. Fourier Split-Step Polar-Coordinate Angular Spectrum Method for Curvilinear Arrays The ultrasonic wave field p(θ,r,f) as a function of position (θ,r) and frequency f can be propagated in the radial range r=r1 to r=r2 using the angular spectrum method in polar coordinate form (Figure 1) [2].

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[0061] FIG. 4 shows the angular spectrum method in polar coordinates for a curvilinear array, as described by Equations 1 and 2 above.

[0062] FIG. 5 illustrates ultrasound pulse-echo imaging based on the time-domain cross-correlation of transmitted and received wave fields.

[0063] C. Shot Profile Migration: Imaging based on correlation of transmitted and received wave fields The ultrasonic pulse-echo image is generated by transmitting elements i=1,...,N tx The transmitted wave field is calculated based on the transmitted sequence and received channel data collected from

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[0072] We show the sound speed estimation and phase aberration correction when applying wave equation velocity analysis (WEMVA) to the reconstructed image.

[0073] D. Wave Equation Velocity Analysis (WEMVA) The following vectorized notation for shot profile migration applies to all forms of the angular spectrum method, regardless of the coordinate system used.

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[0092] The objective function of the wave equation velocity analysis (WEMVA) and its gradient are expressed as follows:

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[0095] The conjugate gradient algorithm, based on the gradient of the objective function, calculates the sound speed profile before coherent synthesis.

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[0098] In some embodiments of the present invention, the Wave Equation Velocity Analysis (WEMVA) method described herein may be modified using a ray-based approach to reduce computational costs related to memory, computational limitations, etc. Such ray-based Wave Equation Velocity Analysis (WEMVA) is further described below.

[0099] A. Delay-and-Sum Beamforming Model First, a multistatic synthetic aperture dataset indexed by single-element transmitter m and receiver n

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[0111] B. Gradient with respect to delay The gradient of the objective function of the wave equation propagation velocity analysis (WEMVA) with respect to delay is expressed as follows:

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[0122] In conventional travel-time tomography, each transmitted image from a single element is assumed to contain an identical receive path back to the transducer. Therefore, the receive paths should all cancel out, so the image

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[0125] However, in this method, which uses rays for wave equation propagation velocity analysis (WEMVA),

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[0129] C. Grouping terms by ray path For m=1,...,N-1 and n=1,...,N, the auxiliary variables

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[0142] Figure 8 shows the delay gradient for the pulse-echo reconstruction of a target point. The image in Figure 8 shows the image of the target point and the induced wavepath between each transmit element and the target point when the image is aligned to the speed of sound cbfm, which is equal to the true speed of sound in the medium ctrue = 1540 m / s.

[0143] Figures 9 and 10 show the WEMVA ray-based wave equation velocity analysis (WEMVA) for two different cases simulating abdominal imaging. Each case shows a B-mode image before aberration correction, an idealized B-mode image using the true sound speed profile, and a corrected B-mode image using sound speeds reconstructed by WEMVA ray-based wave equation velocity analysis (WEMVA). Regularization is used to promote layered structure in the corresponding sound speed reconstructions.

[0144] As known to those skilled in the art, the above mathematical description can be implemented in software resident on a computing device or system having a processor, memory, and access to a computer-readable medium, such a system being described hereinabove and capable of providing improved ultrasound images not previously possible.

[0145] It is therefore apparent that there has been provided, in accordance with various objects of the present invention, a diffraction tomography system for sound speed estimation and aberration correction in medical ultrasound pulse-echo imaging based on propagation velocity analysis.

[0146] While various objects of the present invention have been described in conjunction with preferred embodiments, it is believed that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the specification, drawings, and claims appended hereto.

Claims

1. 1. An improved system for diagnostic ultrasound imaging, comprising: an ultrasound system having a transmit subsystem and a data acquisition subsystem; an ultrasound probe operably connected to the ultrasound system; a signal processing component based on Wave Equation Velocity Analysis (WEMVA) that provides reflectivity images and sound speed maps; an output device configured to receive the reflectance image and the sound speed map; A system having:

2. 10. The system of claim 1, wherein the Wave Equation Velocity Analysis (WEMVA) based signal processing component comprises: a shot profile migration algorithm; Wave Equation Velocity Analysis (WEMVA) algorithm; a sound speed map output from the wave equation velocity analysis (WEMVA) algorithm and input to the shot profile migration algorithm; The system has:

3. 3. The system of claim 2, wherein the Wave Equation Velocity Analysis (WEMVA) based signal processing component further comprises: The system further comprises a coherent combining algorithm configured to receive the reconstructed image from the shot profile migration algorithm and generate a reflectance image.

4. 4. The system according to claim 1, wherein the wave equation velocity analysis (WEMVA) uses rays.

5. 5. The system according to claim 1, wherein the output device is selected from the group consisting of a display device, a digital storage device, or a printer.

6. The system according to any one of claims 1 to 5, further comprising: The system further comprises a network interface operatively connected to the output device.

7. 10. The system of claim 1, wherein the Wave Equation Velocity Analysis (WEMVA) based signal processing component is configured to receive and process received data and transmitted metadata from the ultrasound system.

8. 1. A signal processing system based on wave equation velocity analysis (WEMVA), comprising: a shot profile migration algorithm; Wave Equation Velocity Analysis (WEMVA) algorithm; a sound speed map output from the wave equation velocity analysis (WEMVA) algorithm and input to the shot profile migration algorithm; A signal processing system based on wave equation propagation velocity analysis (WEMVA), comprising:

9. 9. The signal processing system based on wave equation velocity analysis (WEMVA) of claim 8, further comprising: A signal processing system based on wave equation velocity analysis (WEMVA), comprising a coherent combining algorithm configured to receive the reconstructed image from the shot profile migration algorithm and generate a reflectance image.

10. 10. A signal processing system based on Wave Equation Velocity Analysis (WEMVA), wherein the Wave Equation Velocity Analysis (WEMVA) according to claim 8 or 9 uses light rays.

11. 1. A method for iterative image refinement and tissue characterization by speed of sound, comprising: acquiring medical ultrasound pulse-echo data from an ultrasound data acquisition system; applying a shot profile migration algorithm to reconstruct an image from the acquired data; applying a wave equation velocity analysis (WEMVA) algorithm to the reconstructed image to update a sound speed map; providing updated sound speed map data to the shot profile migration algorithm; A method comprising:

12. 12. The method of claim 11, further comprising: providing the updated sound speed map to an output device.

13. 12. The method of claim 11, further comprising: providing a reconstructed image from the shot profile migration algorithm to a coherent combining algorithm; generating a reflectance image from the reconstructed image, which is provided to the shot profile migration algorithm; A method comprising:

14. 14. The method of claim 13, further comprising: providing the reflectance image to an output device.

15. 15. The method of claim 14, further comprising providing the updated sound speed map and the reflectance image to an output device.

16. 16. The method of claim 15, wherein the output device is connected to a network interface.

17. 16. The method of claim 15, wherein the output device is selected from the group consisting of a display device, a digital storage device, or a printer.

18. 12. The method of claim 11, wherein the medical ultrasound pulse-echo data comprises received data and transmitted metadata.

19. 12. The method of claim 11, further comprising: providing the updated sound speed map and the reflectivity image to a network.

20. The method of claim 11 , wherein the Wave Equation Velocity Analysis (WEMVA) algorithm is ray-based.

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