A fast ultrasonic plane wave imaging method based on phase shift

Abstract

The present invention discloses a phase-shift-based ultrasonic plane wave rapid imaging method for accurately and efficiently imaging multi-layer media. This method features reduced data storage and processing requirements, faster reconstruction speed, and deeper penetration depth. To obtain accurate and clear imaging results, two linear array transducers are used to obtain the sound velocity distribution of the imaging area. Based on the sound velocity distribution and the phase-shift algorithm, the sound field is accurately and efficiently extrapolated. Finally, the final images obtained by the two transducers are fused to obtain a high-quality reconstruction result. Under the same conditions, this method can achieve a deeper penetration depth than traditional phase-shift-based synthetic aperture ultrasonic imaging, and can achieve imaging of multi-layer media with five-layer structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of plane wave imaging, and in particular relates to a phase shift-based ultrasonic plane wave rapid imaging method. Background Art

[0002] Plane wave imaging requires only a small number of ultrasound beams to produce high-quality images, significantly improving the temporal resolution of image reconstruction, reaching thousands or even tens of thousands of frames per second. The principle is to transmit plane waves at different angles within the region of interest, receive them simultaneously across all array elements, and then perform coherent composite reconstruction of the image. Plane wave imaging based on delayed-and-stacking beamforming has been widely used in soft tissue imaging research, including transient elastography, Doppler imaging, contrast-enhanced imaging, brain functional imaging, and super-resolution imaging.

[0003] However, when two media have significantly different sound velocities, ultrasound waves can experience significant reflection and refraction at their interface. The existing conventional method is synthetic aperture ultrasound imaging based on phase shift. Each transducer element sequentially transmits ultrasound waves, which are then received by all elements. This requires enormous data storage and computational effort, resulting in low imaging efficiency. Therefore, a more efficient and rapid imaging method is needed for imaging multilayered regular media. Summary of the Invention

[0004] The purpose of the present invention is to provide a phase-shift-based ultrasonic plane wave rapid imaging method, which can achieve accurate and rapid reconstruction imaging of multi-layer media and can be used in medical imaging and non-destructive testing.

[0005] In order to solve the above problems, the technical solution of the present invention is:

[0006] A phase-shift-based ultrasonic plane wave rapid imaging method, comprising:

[0007] Two linear array transducers are placed opposite to each other, and the multi-layer medium to be imaged is placed between the two linear array transducers; each linear array transducer has N array elements, and all array elements transmit N p Ultrasonic pulse signals at various angles are received in a full matrix manner;

[0008] The following sound field signal processing is performed on the sound field collected by the linear array transducer:

[0009] Take the received sound field signal of the i-th emission angle, perform Fourier transform on t, and perform sound field alignment; i = 1, 2, ..., N p , t represents time;

[0010] Perform Fourier transform on the aligned sound field along the x direction;

[0011] The acoustic field is extrapolated using the sound velocity model and phase shift method until the maximum depth of the multilayer medium to be imaged is reached, and the reconstructed acoustic field at the i-th emission angle is obtained.

[0012] The reconstructed sound fields at each emission angle are added together to obtain the reconstructed image of the single-sided linear array transducer;

[0013] The above-mentioned sound field signal processing is performed on the sound field of the other linear array transducer to obtain a reconstructed image of the linear array transducer on the other side, and the images of the linear array transducers on both sides are fused to obtain a complete image.

[0014] According to an embodiment of the present invention, performing sound field alignment further includes:

[0015] The ultrasonic pulse echoes received at different x-axis positions and emission angles of the sound field after Fourier transformation of t are aligned at the arrival time, so that the arrival time of the received ultrasonic pulse echo is t=0.

[0016] According to an embodiment of the present invention, performing sound field extrapolation using a sound velocity model and a phase shift algorithm further includes:

[0017] The sound velocity model is: v = d / Δt;

[0018] Where d is the size of the object being measured, Δt is the difference between the time it takes for the ultrasonic pulse signal to pass through the object being measured and the time it takes for the ultrasonic pulse signal to pass through the reference object;

[0019] The phase shift algorithm is based on the explosion reflection model in geophysics. Under zero offset conditions, the acoustic field signal is received at z=0 and a two-dimensional Fourier transform is performed, where z is the depth of the acoustic field in the multi-layer medium to be imaged.

[0020] The transformed frequency beam domain sound field signal is multiplied by the phase shift factor to obtain the sound field signal at any depth. The sound field signal is then subjected to inverse Fourier transform, and the focusing condition t=0 of the explosion reflection model is substituted into the inverse transformed sound field signal to obtain the reconstructed time domain sound field signal.

[0021] According to an embodiment of the present invention, the sound field is extrapolated using the following extrapolation formula:

[0022]

[0023] in, is the frequency domain sound field signal, is the phase shift factor, Δz is the depth increment of each sound field extrapolation, f is the frequency, k x is the wave vector component in the x direction, Z l is the depth of the lth layer of medium;

[0024]

[0025] Among them, c l is the sound velocity of the lth layer of medium, θ l is the angle between the ultrasonic pulse signal and the horizontal plane in the lth layer of medium;

[0026] The frequency domain sound field signal at the depth increment Δz is continuously obtained through the above extrapolation formula, and then the inverse Fourier transform is performed, and t=0 is substituted into the inverse transformed sound field signal to obtain the reconstructed time domain sound field signal; until the maximum depth, the sound fields at each depth are spliced ​​to obtain the reconstructed image of the current emission angle.

[0027] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0028] In an embodiment of the present invention, the ultrasonic plane wave rapid imaging method based on phase shifting is implemented. Since all array elements transmit together, the signal strength is greater than that of the signal transmitted by a single array element. After the received sound field is aligned, the zero offset condition required by the phase shift algorithm is met. Therefore, there is no need to calculate the delay of each focal point, the reconstruction speed is significantly accelerated, and the imaging efficiency is effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart of a method for rapid ultrasonic plane wave imaging based on phase shift in one embodiment of the present invention;

[0030] Figure 2 Schematic diagram of signal transmission and acquisition of a dual-linear array transducer in one embodiment of the present invention;

[0031] Figure 3 is an imaging result in one embodiment of the present invention;

[0032] Figure 4 3 is a comparison diagram of ultrasonic plane wave rapid imaging based on phase shift using a single-sided transducer in an embodiment of the present invention compared with traditional synthetic aperture ultrasonic imaging. DETAILED DESCRIPTION

[0033] The following is a detailed description of the ultrasonic plane wave rapid imaging method based on phase shift proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0034] The traditional synthetic aperture ultrasound imaging algorithm based on phase shift has the following defects: each element of the transducer transmits sound waves in sequence, and all elements receive them each time, which results in large data storage and processing volume. t ×N e ×N e , where N e is the number of array elements, N tThe number of samples is 100,000. Furthermore, the single-element ultrasound emission results in low energy emission, making it difficult to penetrate media with high acoustic impedance, and the imaging depth is difficult to meet the requirements of thick media. At the same time, synthetic aperture ultrasound imaging based on phase shift requires convolution of the received sound field at each focal point with the simulated sound field to account for the time offset caused by the different transmission and reception paths (which does not meet the zero offset condition required by the phase shift algorithm). Therefore, during phase shift, both the simulated and received sound fields need to be Fourier transformed and inversely transformed, and the sound field extrapolated. Finally, the simulated sound field and the received sound field are convolved to obtain the final reconstruction result, which results in low imaging efficiency.

[0035] The ultrasonic plane wave fast imaging method based on phase shift of the present invention uses all array elements to transmit ultrasonic waves and all array elements to receive them. The data size is N t ×N e ×N p , where N p is the number of plane wave launches, much smaller than N e ; All array elements are emitted, the emission energy of the sound wave is stronger, it can penetrate deeper media to obtain echoes, and the penetration depth is deeper; compared with traditional synthetic aperture ultrasonic imaging based on phase shift, the present invention only needs to perform wave field alignment at the beginning, and then perform a Fourier transform and inverse transform, and the imaging efficiency is significantly improved.

[0036] The ultrasonic plane wave fast imaging method based on phase shift can be found in Figure 1 , including the following steps:

[0037] Step 1: Place two linear array transducers opposite to each other, and place the multi-layer medium to be imaged between the two linear array transducers; each linear array transducer has N array elements, and all array elements emit N p Ultrasonic pulse signals at various angles are received in a full matrix manner;

[0038] Step 2: Process the sound field signals collected by the array transducer as follows:

[0039] Take the received sound field signal of the i-th emission angle, perform Fourier transform on t, and perform sound field alignment; i = 1, 2, ..., N p , t represents time;

[0040] Step 3: Perform Fourier transform on the aligned sound field along the x-direction;

[0041] Step 4: Use the sound velocity model and phase shift method to extrapolate the sound field until the maximum depth of the multi-layer medium to be imaged, and obtain the reconstructed sound field at the i-th emission angle;

[0042] Step 5: Add the reconstructed sound fields of each emission angle to obtain a reconstructed image of the single-sided linear array transducer;

[0043] Step 6: Process the sound field signal of the other linear array transducer to obtain a reconstructed image of the linear array transducer on the other side, and fuse the images of the linear array transducers on both sides to obtain a complete image.

[0044] In step 1, two identical linear array ultrasonic transducers are placed in parallel and aligned, each having N array elements. The multilayer medium to be imaged is placed between the two ultrasonic transducers, and water is poured into the water tank to immerse the sample and the ultrasonic transducers.

[0045] Please see Figure 2 All array elements of the two ultrasonic transducers transmit ultrasonic pulse signals at a fixed center frequency and a certain delay, forming a plane wave front with an angle of θ with the horizontal plane, and receive ultrasonic pulse echo signals in a full matrix manner through all array elements, transmitting a total of N p angles. The center frequency of the ultrasonic transducer is 3.5MHz, the array element width is 0.2mm, the center distance between adjacent array elements is 0.3mm, and the effective aperture length is 38.4mm. The transmitting signal of each array element is a 2-cycle Gaussian envelope sine wave. 15 transmitting angles (evenly spaced) are selected to excite and generate plane waves. The sampling frequency is 25MHz. During the PSM migration process, the depth direction wave field extrapolation step size is 0.044mm. In this embodiment, N e =128, N p =15.

[0046] In step 2, for the sound field collected by the ultrasonic transducer on one side, the received sound field signal emitted at the i-th angle is Fourier transformed, and the sound field is aligned. That is, the echoes of the reflected objects received at different x-axis positions and emission angles after the Fourier transformation are aligned at the arrival time, so that That is, the arrival time of the echo received from the reflected object is always t=0.

[0047] In step three, the aligned sound field is Fourier transformed along the x-direction.

[0048] In step 4, the sound field is extrapolated using the sound velocity model and phase migration algorithm. The extrapolation starts from Z0 and uses the extrapolation formula Where f is the frequency, k x The wave vector component in the x direction is used to continuously obtain the frequency domain size of the sound field at the depth increment Δz, and then perform inverse Fourier transform and substitute t = 0 to obtain the reconstructed time domain sound field value until the maximum depth. The sound fields at each depth are spliced ​​to obtain the complete reconstructed image of the i-th emission angle. The sound velocity of the l-th layer related to the depth is c l ,

[0049] The sound velocity model of the object under test is measured using the simplest method: v = d / Δt, where d is the size of the object under test, measured with a vernier caliper (with an accuracy of 0.01 mm), and Δt is the difference in flight time between the ultrasonic signal passing through the object under test and a reference object. To minimize errors, four measurements are performed at different locations on the object under test and the average is taken. In this example, a cortical bone cube was used as the test object. The measured sound velocity of the cortical bone phantom was 3019 m / s, while the sound velocity of water was 1500 m / s.

[0050] Phase shift is based on the explosion reflection model in geophysics. In the case of zero offset, the received sound field at z = 0 is transformed into a two-dimensional Fourier transform, and the transformed sound field in the frequency beam domain is multiplied by the phase shift factor. The sound field at any depth is obtained, and then subjected to an inverse Fourier transform. The focusing condition t = 0 of the explosion reflection model is substituted into the sound field to obtain the reconstructed time-domain sound field value. Because the phase shift method extrapolates in the depth direction, it is particularly suitable for imaging media with varying sound velocity in the depth direction.

[0051] In step five, for the next emission angle, steps two to four are repeated until the last emission angle is reached, and the reconstructed sound fields of each emission angle are added together to obtain a reconstructed image of the single-sided transducer.

[0052] In step 6, repeat steps 2 to 5 for the other transducer and fuse the reconstructed images of both sides to obtain a complete imaging result. Figure 3 The inner and outer boundaries of the cortical bone are clearly and accurately reconstructed, and their shape and position are highly consistent with the real model. The location of the cortical bone is 5mm-7.5mm and 10mm-12.5mm.

[0053] The ultrasonic plane wave fast imaging method based on phase shift in this embodiment can achieve accurate and efficient imaging of multi-layer media. And compared with the traditional synthetic aperture method based on phase shift, it can be seen that the present invention obtains an imaging result with a deeper imaging depth through plane wave emission, which makes up for the shortcomings of the traditional synthetic aperture algorithm for imaging multi-layer media. Figure 4 , under the same dynamic range, the traditional synthetic aperture ultrasound imaging method based on phase shift ( Figure 4 (a)) can only see the upper surface of the upper cortical bone, while the method used in the present invention ( Figure 4 (b) shows the complete upper cortical bone and the upper surface of the lower cortical bone. It can be seen that the imaging depth of the ultrasonic plane wave fast imaging algorithm based on phase shift is much higher than that of the traditional synthetic aperture ultrasound imaging algorithm based on phase shift.

[0054] In summary, the phase-shift-based ultrasonic plane wave rapid imaging method in this embodiment accurately and efficiently images multi-layer media. This method has smaller data storage and processing volume, faster reconstruction speed, and deeper penetration depth. In order to obtain accurate and clear imaging results, two linear array transducers are used to obtain the sound velocity distribution of the imaging area, and the sound field is accurately and efficiently extrapolated based on the sound velocity distribution and phase shift algorithm. Finally, the final image obtained by the two transducers is fused to obtain a high-quality reconstruction result. Under the same conditions, it can achieve a deeper penetration depth than traditional phase-shift-based synthetic aperture ultrasonic imaging, and can achieve multi-layer media imaging with a five-layer structure.

[0055] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the scope of protection of the present invention.

Claims

1. A method for rapid ultrasonic plane wave imaging based on phase shift, characterized in that: include: Two linear array transducers are placed opposite to each other, and the multi-layer medium to be imaged is placed between the two linear array transducers; each linear array transducer has N array elements, and all array elements transmit N p Ultrasonic pulse signals at various angles are received in a full matrix manner; The following sound field signal processing is performed on the sound field collected by the linear array transducer: Take the received sound field signal of the i-th emission angle, perform Fourier transform on t, and perform sound field alignment; i = 1, 2, ..., N p , t represents time; Perform Fourier transform on the aligned sound field along the x direction; The acoustic field is extrapolated using the sound velocity model and phase shift method until the maximum depth of the multilayer medium to be imaged is reached, and the reconstructed acoustic field at the i-th emission angle is obtained. The reconstructed sound fields at each emission angle are added together to obtain the reconstructed image of the single-sided linear array transducer; The above-mentioned sound field signal processing is performed on the sound field of the other linear array transducer to obtain a reconstructed image of the linear array transducer on the other side, and the images of the linear array transducers on both sides are fused to obtain a complete image.

2. The ultrasonic plane wave rapid imaging method based on phase shift according to claim 1, wherein: Performing sound field alignment further includes: The ultrasonic pulse echoes received at different x-axis positions and emission angles of the sound field after Fourier transformation of t are aligned at the arrival time, so that the arrival time of the received ultrasonic pulse echo is t=0.

3. The ultrasonic plane wave rapid imaging method based on phase shift according to claim 1, wherein: The sound field extrapolation using the sound velocity model and phase shift algorithm further includes: The sound velocity model is: v = d / Δt; Where d is the size of the object being measured, Δt is the difference between the time it takes for the ultrasonic pulse signal to pass through the object being measured and the time it takes for the ultrasonic pulse signal to pass through the reference object; The phase shift algorithm is based on the explosion reflection model in geophysics. Under zero offset conditions, the acoustic field signal is received at z=0 and a two-dimensional Fourier transform is performed, where z is the depth of the acoustic field in the multi-layer medium to be imaged. The transformed frequency beam domain sound field signal is multiplied by the phase shift factor to obtain the sound field signal at any depth. The sound field signal is then subjected to inverse Fourier transform, and the focusing condition t=0 of the explosion reflection model is substituted into the inverse transformed sound field signal to obtain the reconstructed time domain sound field signal.

4. The method for rapid ultrasonic plane wave imaging based on phase shift according to claim 3, wherein: The sound field is extrapolated using the following extrapolation formula: in, is the frequency domain sound field signal, is the phase shift factor, Δz is the depth increment of each sound field extrapolation, f is the frequency, k x is the wave vector component in the x direction, Z l is the depth of the lth layer of medium; Among them, c l is the sound velocity of the lth layer of medium, θ l is the angle between the ultrasonic pulse signal and the horizontal plane in the lth layer of medium; The frequency domain sound field signal at the depth increment Δz is continuously obtained through the above extrapolation formula, and then the inverse Fourier transform is performed, and t=0 is substituted into the inverse transformed sound field signal to obtain the reconstructed time domain sound field signal; until the maximum depth, the sound fields at each depth are spliced ​​to obtain the reconstructed image of the current emission angle.

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