4D ultrasonic imaging system and method based on partitioned electrodes and compressive sensing

Abstract

The invention discloses a four-dimensional (4D) ultrasonic imaging system and method based on partitioned electrodes and compressive sensing. The backing, the piezoelectric ceramic and the matching layer are sequentially installed in the shell, the positive electrode of the piezoelectric ceramic serves as a sound radiation surface and faces a target area through the matching layer, the backing used for absorbing reflected waves is placed on the negative electrode of the piezoelectric ceramic, and the piezoelectric ceramic is electrically connected with the control circuit through a cable penetrating out of the shell. The space phase mask is installed outside the shell, makes contact with the face, away from the piezoelectric ceramic, of the matching layer and is used for modulating space phase distribution of transmission sound waves. The acoustic radiation surface of the piezoelectric ceramic is divided into a plurality of electrode areas, each electrode area is electrically connected with the control circuit, the control circuit is used for controlling independent excitation and receiving of each electrode area, and the negative electrode of the piezoelectric ceramic is grounded. Compared with a traditional phased array device, the complexity and the operation cost of the device are greatly reduced, and the problem that in the prior art, it is difficult to rotate or move a mask to increase additional signal measurement values is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic non-destructive testing, and in particular to a 4D ultrasonic imaging system and method based on partitioned electrodes and compressed sensing. Background Art

[0002] Ultrasound imaging is widely used in industrial inspection and biomedicine. By moving an ultrasonic probe, images of the inspected cross-section can be acquired. The principle is that the ultrasonic probe emits an ultrasonic pulse signal (typically with a frequency of 1 to 20 MHz) and simultaneously receives the reflected echo from the target area. By analyzing the time between pulse emission and echo, the location of the imaging target can be inferred. Common ultrasonic phased array probes are primarily made of piezoelectric ceramics arranged in an array. When voltage is applied to the material, the piezoelectric crystals vibrate and generate short ultrasonic pulses of several cycles. When the relevant array elements are activated with an appropriate delay, the transmitted sound waves propagate in a narrow beam, focusing on the point of interest. These focused beams can be used to scan an entire volume. When receiving the signal, similar delays can be used to selectively enhance the signal from scatterers in the beam of interest. This focusing method, which uses delayed signals during transmission and / or reception, is called beamforming and has been widely researched and applied for many years.

[0003] 4D imaging technology (real-time three-dimensional dynamic imaging), an innovative achievement of interdisciplinary integration, has become a cutting-edge research direction. In the field of industrial nondestructive testing, 4D ultrasound has been applied to the real-time three-dimensional localization of internal defects in materials. In the biomedical field, 4D ultrasound combined with Doppler hemodynamic analysis enables the analysis of heart valve kinematics and the quantitative evaluation of tumor angiogenesis. However, current real-time three-dimensional dynamic imaging technologies rely on beamforming optimization of phased array ultrasound probes and iterations of parallel computing architectures (post-processing of the individual signals received by each array element after analog-to-digital conversion). This often requires dozens of sensor elements, complex hardware, and cumbersome signal processing logic. Recent discoveries in compressed sensing suggest that signal structure can be exploited to alleviate the burden imposed by traditional phased array ultrasound imaging requirements.

[0004] The core of compressed sensing is to destroy the phase uniformity of the sound wave during transmission and reception, thereby projecting the 3D object information onto a set of incoherent basis functions. This involves placing a phase-encoding mask in front of the ultrasound probe to change the time it takes for the ultrasound wave to propagate into the target medium. This destroys the phase uniformity of the sound wave, producing a complex spatiotemporal interference pattern. Therefore, for each position (each pixel) in 3D space, there is a unique ultrasound signal from that position. The echo signals of all pixels are collected by the ultrasound probe after passing through the mask, resulting in a compressed measurement value. At this point, the actual scene signal can be reconstructed by inversely analyzing the compressed measurement value. However, due to the limitations of the temporal bandwidth and the specific phase distribution of the mask, it cannot be guaranteed that the echo signals of all pixels are uncorrelated. To this end, researchers currently rotate or move the mask to add additional signal measurements, but this is difficult to operate and implement in actual detection. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a 4D ultrasonic imaging system and method based on partitioned electrodes and compressed sensing.

[0006] The technical solution adopted in the present invention is:

[0007] The present invention includes a housing, a cable, a backing, a piezoelectric ceramic, a matching layer, a spatial phase mask, and a control circuit. The backing, piezoelectric ceramic, and matching layer are sequentially installed in the housing. The positive surface of the piezoelectric ceramic serves as the sound radiation surface and faces the target area. The negative surface of the piezoelectric ceramic is placed with a backing for absorbing reflected waves. The piezoelectric ceramic is electrically connected to the control circuit via a cable passing through the housing. The spatial phase mask is installed outside the housing and contacts a surface of the matching layer away from the piezoelectric ceramic, and is used to modulate the spatial phase distribution of the transmitted sound wave.

[0008] The sound radiation surface of the piezoelectric ceramic is divided into L×L electrode areas, each electrode area is electrically connected to a control circuit, and the control circuit is used to control the independent excitation and reception of each electrode area. The negative electrode of the piezoelectric ceramic is grounded.

[0009] Also included is a compressed sensing linear module, the compressed sensing linear module being electrically connected to the control circuit and configured to reconstruct a 4D ultrasound image of the target area;

[0010] It also includes a locking knob, which is arranged on the upper end surface of the shell and is used to fix the cable passing through the shell.

[0011] The size of the spatial phase mask is the same as that of the piezoelectric ceramic and the spatial phase mask is divided into L×L mask areas. The thickness of each mask area is different and the thickness relationship between the mask areas is set to satisfy the spatial phase difference between the transmitted waves of any two mask areas in the spatial phase mask is greater than or equal to 0 and less than or equal to π. The spatial phase difference between the transmitted waves of the two mask areas is set according to the following formula:

[0012] φ=arg(P1-P2)

[0013] Wherein, φ represents the spatial phase difference of the transmitted wave, arg() represents the complex argument, and P1 and P2 are the complex representations of the transmitted waves of the two mask areas respectively.

[0014] The backing and matching layer are both made of epoxy resin mixed with tungsten powder, the mass ratio of tungsten powder to epoxy resin in the backing is (2-4):1, the mass ratio of tungsten powder to epoxy resin in the matching layer is 1:(3-5), and the thickness of the matching layer is equal to one-quarter of the wavelength of the center frequency of the piezoelectric ceramic.

[0015] The sound radiation surface of the piezoelectric ceramic is divided into a plurality of electrode areas in any of the following ways: laser cutting, dicing cutting or sputtering deposition of a metal electrode layer on the piezoelectric ceramic.

[0016] The sound radiation surface of the piezoelectric ceramic is provided with a multi-electrode flexible circuit board or a needle-shaped electrode.

[0017] The 4D ultrasound imaging method includes the following steps:

[0018] S1. Scan the target area with wave fields to obtain the system matrix, and then establish a linear system model based on the system matrix;

[0019] S2, randomly controlling the electrode area of the piezoelectric ceramic so that the piezoelectric ceramic emits ultrasonic waves, which are modulated by a spatial phase mask and reflected by the target area to obtain an echo signal;

[0020] S3, the echo signal passes through the spatial phase mask and is received by the piezoelectric ceramic to form a compression signal, which is then recorded by the control circuit and transmitted to the linear system model;

[0021] S4. Repeat steps S2 and S3 multiple times and randomly control the electrode area of the piezoelectric ceramic each time until the linear system model receives S compression signals. The linear system model reconstructs the 4D ultrasound image of the target area based on the S compression signals.

[0022] The wavefield scanning is performed according to the following method:

[0023] A hydrophone is used to collect ultrasonic waves modulated by a spatial phase mask in a plane perpendicular to the propagation direction of the ultrasonic wave. The ultrasonic waves modulated by the spatial phase mask are then processed to obtain wavefield data. Subsequently, the angular spectrum method is used to propagate the wavefield data to planes with different propagation distances to obtain wavefield data of different propagation distances. The system matrix is then constructed based on the wavefield data of different propagation distances.

[0024] The linear system model reconstructs the 4D ultrasound image of the target area according to the following formula:

[0025] u=Hv+n

[0026] Where u represents the compressed signal, v represents the reconstructed 4D ultrasound image signal, n represents the noise signal, and H is the system matrix.

[0027] The beneficial effects of the present invention are:

[0028] The present invention uses a single ultrasonic transducer with only electrode partitions in combination with a phase mask to achieve dynamic three-dimensional imaging. Compared with complex and expensive phased array systems and other signal acquisition methods, it significantly reduces equipment costs and greatly increases the operational portability of the equipment. By randomly activating different areas each time to collect multiple groups of "multiple transmit and one receive" signals, it effectively solves the problem of the existing technology that it is difficult to rotate or move the mask to increase additional signal measurement values. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 4D ultrasonic imaging system assembly diagram.

[0030] Figure 2 4D ultrasonic imaging system is an exploded view.

[0031] Figure 3 4D ultrasonic imaging system electrode wiring diagram.

[0032] Figure 4 4D ultrasonic imaging system spatial phase mask structure schematic diagram.

[0033] Figure 5 Schematic diagram of a compressed sensing linear module of the 4D ultrasound imaging method.

[0034] Figure 6 It is a flow chart of the working process of the 4D ultrasound imaging method.

[0035] Figure 7 1 is a schematic diagram of a simulated defect in Example 1 of the 4D ultrasonic imaging method.

[0036] Figure 8 This is an imaging result diagram of Example 1 of the 4D ultrasound imaging method.

[0037] Figure 9 This is a schematic diagram of a simulated defect in Example 2 of the 4D ultrasonic imaging method.

[0038] Figure 10 This is an imaging result diagram of Example 2 of the 4D ultrasound imaging method.

[0039] Reference numerals: 1 housing, 2 locking knob, 3 cable, 4 backing, 5 piezoelectric ceramic, 6 matching layer, 7 spatial phase mask. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the accompanying drawings and examples. The embodiments of the present invention include but are not limited to the following examples.

[0041] In the description of the present invention, it should be understood that the terms "hollow", "top", "bottom", "inside", "outside" and the like indicating orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0042] like Figure 1 and Figure 2 As shown, the 4D ultrasonic imaging system includes a housing 1, a cable 3, a backing 4, a piezoelectric ceramic 5, a matching layer 6, a spatial phase mask 7 and a control circuit. The backing 4, the piezoelectric ceramic 5 and the matching layer 6 are sequentially arranged in the housing 1. The positive surface of the piezoelectric ceramic 5 serves as an acoustic radiation surface and emits ultrasonic waves toward the target area. The negative surface of the piezoelectric ceramic 5 is provided with the backing 4 for absorbing reflected waves. The piezoelectric ceramic 5 is electrically connected to the control circuit via the cable 3 passing through the housing 1. The spatial phase mask 7 is installed on the outside of the housing 1 and contacts a surface of the matching layer 6 away from the piezoelectric ceramic 5 to modulate the spatial phase distribution of the transmitted acoustic wave.

[0043] The sound radiation surface of the piezoelectric ceramic 5 is divided into L×L electrode areas, each of which is electrically connected to a control circuit. The control circuit is used to control the independent excitation and reception of ultrasonic waves in each electrode area. Therefore, the control circuit can realize simultaneous excitation of a single electrode area or multiple electrode areas. The surface where the negative electrode of the piezoelectric ceramic 5 is located is grounded.

[0044] The reflected waves absorbed by the backing 4 are the reflected waves when the ultrasonic waves emitted from the piezoelectric ceramic 5 hit the backing 4 , and the backing 4 prevents the ultrasonic waves from returning to the piezoelectric ceramic 5 again.

[0045] Electrode layers are provided on both sides of the piezoelectric ceramic 5, and the electrode layers are electrically connected to the drive output terminal of the control circuit through the cable 3. The control circuit can be connected to an oscilloscope to observe and analyze the compression signal.

[0046] The sound radiation surface of the piezoelectric ceramic 5 and its control circuit are different from those of the phased array ultrasonic transducer. They do not have complex logic circuits and do not control the excitation timing of each array element through electronic delay. Instead, the electrode area uses the control circuit to achieve multi-element coordinated control such as one-shot all-receive and multiple-shot all-receive. The structure is simpler than the existing 4D ultrasonic imaging system.

[0047] The cable 3 includes several lines. Each electrode area is connected to the control circuit using a separate line. The negative electrode of the piezoelectric ceramic 5 is connected to the ground terminal in the control circuit using a line. Therefore, the number of lines in the cable 3 is equal to the number of electrode areas plus one.

[0048] The 4D ultrasonic imaging system further includes a compressed sensing linear module, which is electrically connected to the control circuit and is configured to receive a compressed signal transmitted by the control circuit and thereby reconstruct a 4D ultrasonic image of the target area;

[0049] It also includes a locking knob 2 , which is arranged on the upper end surface of the housing 1 and is used to fix the cable 3 passing through the housing 1 .

[0050] The spatial phase mask needs to be divided into regions according to the number of electrode partitions. For one region of the mask, the transmitted acoustic field after the modulated incident plane wave with a frequency of f can be expressed as v a is the sound velocity of the mask material, k a represents the wave velocity of the mask material, where k a =2πf / v a is the wave number of the material, and the transmitted sound field at units of different thickness h is different.

[0051] like Figure 4 As shown, the spatial phase mask 7 is the same size as the piezoelectric ceramic 5 and is divided into L×L mask areas in the same manner as the acoustic radiation surface electrode area of the piezoelectric ceramic 5. The thickness of each mask area is different and the thickness relationship between the mask areas is set to satisfy the spatial phase difference between the transmitted waves of any two mask areas in the spatial phase mask 7 is greater than or equal to 0 and less than or equal to π. The spatial phase difference of the transmitted wave is set according to the following formula:

[0052] φ=arg(P1-P2)

[0053] Wherein, φ represents the spatial phase difference of the transmitted wave, arg() represents the complex argument, and P1 and P2 represent the complex representations of the transmitted waves of the two mask areas, respectively.

[0054] z=r(cosθ+isinθ), where r is the modulus of z, r=|z|; θ is the complex argument of z, θ=arg(z).

[0055] The transmitted wave is a wave modulated by the spatial phase mask 7, and the spatial phase difference of the transmitted waves is the phase difference between the two transmitted waves.

[0056] Once fabricated, the spatial phase mask 7 can be directly mounted in front of the single, zoned electrode probe. The spatial phase of the mask can be randomly distributed. Spatial phase mask 7 can be manufactured, but is not limited to, by subtractive manufacturing, 3D printing, or using phase-change polymer materials with varying acoustic velocity on a single flat surface. This disrupts the phase uniformity of the propagating wave, resulting in a random, deterministic interference pattern in the medium. Generally, additive or subtractive manufacturing methods, such as 3D printing and zone drilling, are used to prepare spatial phase milling with randomized height regions. It is important to note that to ensure optimal acoustic wave transmission efficiency, the selected material must have a low acoustic attenuation coefficient and an acoustic impedance that closely matches that of water.

[0057] Specifically, the spatial phase mask 7 is divided into several mask areas in the same way as the electrode area of the sound radiation surface of the piezoelectric ceramic 5, that is, the mask areas divided by the spatial phase mask 7 are the same in number and size as the electrode areas divided by the sound radiation surface of the piezoelectric ceramic 5, and the mask areas divided by the spatial phase mask 7 correspond one-to-one to the electrode areas divided by the sound radiation surface of the piezoelectric ceramic 5.

[0058] Both the backing 4 and the matching layer 6 are made of epoxy resin mixed with tungsten powder. The mass ratio of tungsten powder to epoxy resin in the backing 4 is (2-4):1, and the mass ratio of tungsten powder to epoxy resin in the matching layer 6 is 1:(3-5). The thickness of the matching layer 6 is equal to one-quarter of the center frequency wavelength of the piezoelectric ceramic 5.

[0059] Use spin coating to evenly apply a matching layer with uniform thickness. Generally, the thickness of the matching layer is preferably one-quarter of the wavelength of the center frequency of the piezoelectric chip in water.

[0060] The sound radiation surface of the piezoelectric ceramic 5 is divided into several electrode areas in any of the following ways: laser cutting, dicing cutting or sputtering deposition of a metal electrode layer on the piezoelectric ceramic 5 , that is, adding a partition mask when sputtering the original electrode metal coating.

[0061] The piezoelectric ceramic 5 requires a laser or other scribing device to divide one side of the electrode into sections. The sectioned electrodes must be connected using separate circuits, while the electrodes on the other side of the wafer can share a common circuit. Generally, the positive electrode of the piezoelectric ceramic 5 is preferably used as the electrode section, and the negative electrode can be connected to the common ground circuit. It should be noted that to ensure that a single area within a section can be excited independently, the surface electrode of the piezoelectric ceramic 5 can be divided while increasing the division depth.

[0062] like Figure 3Figure 2 shows a schematic diagram of the control circuitry for a single probe with zoned electrodes. This example uses a single-probe transducer with 64 zones as an example. The positive lead of each zone is individually connected to an analog electronic switch on the controller, while the negative lead is connected to a common ground. The controller's analog switch independently switches signals at high speed. Furthermore, this allows for simultaneous excitation of a single probe zone or multiple zones. A BNC port is also provided for connecting a signal generator to receive and transmit echo signals.

[0063] The sound radiation surface of the piezoelectric ceramic 5 is provided with a multi-electrode flexible circuit board or a needle-shaped electrode, and the negative electrode of the piezoelectric ceramic 5 is welded to the ground.

[0064] The 4D ultrasound imaging system follows the core concept of compressive imaging: projecting object / image information onto a single measurement value via a set of incoherent functions, and then decoding the retrieved measurement value to form an image. Based on this, the solution comprises a single probe with partitioned electrodes, which transmits acoustic waves modulated by a random mask, thereby perturbing the phase of the wavefield. The phase-delay mask ensures that each region in the image is uniquely identifiable during the compressive measurement. By randomly activating different regions each time, multiple sets of "multiple transmit and one receive" signals are collected. Through real-time signal post-processing, dynamic 3D imaging is achieved.

[0065] like Figure 6 As shown, the 4D ultrasound imaging method includes the following steps:

[0066] S1. Use a hydrophone to scan the wave field of the target area to obtain the system matrix H, and then establish a linear system model based on the system matrix H;

[0067] The 4D ultrasonic imaging system can be applied to fields such as underwater ultrasonic detection and medical ultrasound. The target area refers to the spatial area where 4D imaging is required, which can be an underwater detection object or human tissue.

[0068] Since the acoustic impedance of the human body and water is similar, the system matrix obtained in water can still be used when the application scenario is medical ultrasound.

[0069] S2. Randomly control the electrode area of the piezoelectric ceramic 5 so that the piezoelectric ceramic 5 emits ultrasonic waves, which are modulated by the spatial phase mask 7 and then reflected by the target area to obtain an echo signal;

[0070] S3. Due to the phase modulation effect of the mask, the reflected signals at different spatial positions are superimposed in an incoherent manner. The echo signal passes through the spatial phase mask 7 and is received by the piezoelectric ceramic 5 to form a compressed signal, which is then recorded by the control circuit and transmitted to the linear system model.

[0071] S4. Repeat steps S2 and S3 multiple times and randomly control the electrode area of the piezoelectric ceramic 5 each time until the linear system model receives S compression signals, so that the linear system model obtains sufficient information for reconstruction. The linear system model reconstructs the 4D ultrasound image of the target area based on the S compression signals.

[0072] Wavefield scanning is performed as follows:

[0073] A small hydrophone is used to collect ultrasonic waves modulated by the spatial phase mask 7 in a plane close to the surface of the spatial phase mask 7 and perpendicular to the propagation direction of the ultrasonic waves. The ultrasonic waves modulated by the spatial phase mask 7 are then processed to obtain wave field data. Subsequently, the angular spectrum method is used to propagate the wave field data to planes with different propagation distances to obtain wave field data of different propagation distances. Then, a system matrix is constructed based on the wave field data of different propagation distances.

[0074] The planes in the wave field scan are all perpendicular to the ultrasonic wave propagation direction.

[0075] Before imaging, the block matrix H must be acquired in advance to understand the entire spatiotemporal wavefield. Furthermore, a small hydrophone can be used to collect the pulse signal in a plane close to the mask surface and perpendicular to the ultrasonic propagation axis. The recorded wavefield can then be propagated to any plane parallel to the recording plane using the angular spectrum method.

[0076] Specifically, the transmitted sound field collected by the hydrophone is:

[0077] p0(x,y,z=0)=e (iφ0)

[0078] Among them, p0(x, y, z=0) represents the initial transmitted sound field distribution on the plane z=0, indicating the state of the sound field at the plane z=0.

[0079] Then, the frequency spectrum of the plane at this time can be calculated by Fourier transform:

[0080] P0(k x ,k y ,z=0)=∫∫p0(x,y,z=0)dxdy

[0081] Among them, P0(k x ,k y ,z=0) is the spectrum of the transmitted sound field, which is expressed in the frequency domain on the z=0 plane, k x , k y is the spatial wave number of the spectrum in the x and y directions.

[0082] Then, the transmitted sound field propagates forward along the z-axis, and the spectrum is multiplied by the phase conversion factor:

[0083] H(kx ,k y ,z=l)=e (ikzl)

[0084] Then the spectrum distribution on any plane z=l can be obtained:

[0085] P ’ (k x ,k y ,z=l)=P0(k x ,k y ,z=0)*H(k x ,k y ,z=l)

[0086] At this time, the sound field distribution on the plane can be obtained by inverse Fourier transform:

[0087] p ’ (x,y,z=l)=∫∫P ’ (k x ,k y ,z=l)dk x dk y

[0088] Where p0 is the initial sound field collected by the hydrophone at z = 0, φ0 is the initial sound field phase collected by the hydrophone at z = 0, and H is the phase conversion factor used to adjust the spectrum after propagation.

[0089] According to the reciprocity theorem, the pulse-echo signal is obtained by self-convolution of the propagating hydrophone signal. Therefore, the pulse-echo ultrasonic signal of each point in 3D space can be calculated. After multiple random switching, the H column can be filled with data collected and calculated.

[0090] The linear system model reconstructs the 4D ultrasound image of the target area according to the following formula:

[0091] u=Hv+n

[0092] Where u represents the compressed signal, i.e., the actual detection signal; v represents the reconstructed 4D ultrasound image signal, i.e., the unknown true image; n represents the noise signal; and H is the system matrix, i.e., the pulse echo ultrasound signal of each point in the original space-time wave field.

[0093] Specifically, the system matrix H in the linear system model needs to be obtained in advance. After the linear system model is established, the image reconstruction can be completed by inverting the vector v according to the compressed signal u. Multiple sets of "multi-transmit and all-receive" signals are collected by randomly activating different areas each time. Multiple random excitations can eliminate the ambiguity of the reconstructed image and greatly improve the signal-to-noise ratio of the detection target, thereby realizing efficient three-dimensional imaging of the detection target. Based on the rapid switching characteristics of several electrode areas on the sound radiation surface, multiple continuous random acquisitions and processing can be performed within a certain period of time, and dynamic three-dimensional imaging can be achieved by coordinating the probe movement and acquisition.

[0094] Different from the standard beamforming technology in traditional phased array ultrasound, random excitation of several areas of a single probe can achieve incoherent wavefront emission. Correspondingly, the echo is also modulated by the mask and received by the piezoelectric ceramic 5. Therefore, the received compressed signal is regarded as a linear combination of the echo signal of the point scatterer, so as to establish a linear imaging model. The 3D scene contains N pixels in total, u is the actual detection signal, that is, the received compressed signal, and v represents the reconstructed 4D ultrasound image signal, that is, the unknown real image. Figure 5 As shown, the linear imaging model is given by the following formula: u = Hv + n, where u is an M-dimensional column vector, H is an M×N-dimensional block matrix determined by the target area medium, v is an N-dimensional column vector, and n is an M-dimensional column vector whose samples represent zero-mean additive white Gaussian noise with a noise variance of σ e 2 .

[0095] Due to the limitations of time bandwidth and mask thickness distribution, it is not possible to guarantee that the echo signals in all regions are uncorrelated. To introduce more diversity between regions, we choose to collect S groups of different random excitation echoes to obtain additional measurements containing new information. The structure of the block matrix H is as follows:

[0096] H=[H1,H2,H3…H S ] T

[0097] H r =[h r,1 ,h r,2 …,h r,N ]

[0098] Among them H r is a K×N matrix, r∈{1,…,S}, representing the time series of pulse-echo responses of length K at pixel n∈{1…N} in the image, each time a different array element is randomly switched. Therefore, M=KS, and u is also a column vector combination of S K-dimensional column vectors.

[0099] After establishing the linear imaging model, image reconstruction requires solving the inverse vector v. Comparing the measured value M with the number of pixels N to be reconstructed, the linear system is underdetermined (M < N) at this time, and there are infinitely many possible solutions Satisfy Here we choose to use the minimization cost function to find The optimal solution of: Matrix inversion can be implemented and calculated by the preconditioned conjugate gradient method (PCG), and finally we can solve To characterize the accuracy of image reconstruction, the peak signal-to-noise ratio is defined as:

[0100]

[0101] The mean square error is:

[0102]

[0103] Among them, PSNR represents the peak signal-to-noise ratio, and MSE represents the mean square error.

[0104] Example 1:

[0105] First, select a piezoelectric ceramic sheet with a frequency of 5 MHz. Use a laser marking machine to divide the electrodes on one side into 16x16 areas. After the division, use a flexible FPC circuit board with 256 contacts to weld the electrodes. At the same time, weld the negative electrode on the other side to the common negative connection of the circuit board. Then fill the backing and assemble the piezoelectric ceramic sheet into the housing, and spin-coat the matching layer, controlling the thickness of the matching layer to be about one-quarter of the wavelength of this frequency in water, that is, about 75 um.

[0106] Furthermore, use 3D printing technology to prepare a phase delay mask (between 0 and h) with 256 randomly distributed high and low levels. The selected resin sound velocity for 3D printing is 2350 m / s, and the sound velocity of the comparison water is 1450 m / s. When the thickness h is 0.85 mm, the phase delay of the incident wave can be modulated to π. Subsequently, paste the delay mask on the probe surface using ordinary water-based ultrasonic coupling agent.

[0107] Furthermore, after completing the assembly of the partitioned electrode single probe system, at this time, immerse the probe in water and use a hydrophone to collect the wave field near the mask, and record the transmitted sound field at this time as p0(x,y,z = 0). Use the angular spectrum method to obtain the sound field on any plane as P ’ (k x ,k y [[ID=4OA0]],z = l). Furthermore, we perform self-convolution on the collected hydrophone signal itself to obtain the pulse echo signal. Randomly switch 100 of these regions for transmission and use all regions for collection multiple times, and then fill the block matrix H in the linear system.

[0108] Such as Figure 7, set up a simulated target area, then use the probe system to scan the target area, switch different areas to transmit multiple times and use all areas to receive echoes, and solve the linear equation to complete the target area image reconstruction. Figure 8 After multiple switching areas and acquisition, the peak signal-to-noise ratio of the detection imaging is 17.2123dB, which can clearly identify simulated defects. Dynamic 3D imaging can be completed by moving to other areas in real time.

[0109] Example 2:

[0110] First, a 5MHz piezoelectric ceramic sheet was selected. A laser marker was used to divide the electrodes on one side into 12x12 sections. After this division, the electrodes were soldered to a flexible printed circuit board (FPC) with 144 contacts. Simultaneously, the negative electrode on the other side was soldered to the common negative connection on the circuit board. The piezoelectric ceramic sheet was then assembled into a housing, filled with a backing, and spin-coated with a matching layer. The thickness of the matching layer was controlled to be approximately 75µm, a quarter of the wavelength of the frequency in water.

[0111] Furthermore, a CNC machining center was used to machine 144 phase delay masks (between 0 and h) with uneven depth distribution on a flat plate. The selected resin material has a sound velocity of 2350 m / s, compared to the sound velocity of water (1450 m / s). With a thickness of h of 0.85 mm, the incident wave phase delay can be modulated to π. The delay masks were then attached to the probe surface using a standard water-based ultrasonic couplant.

[0112] Furthermore, after the partition electrode single probe system is assembled, the probe is immersed in water and the wave field near the mask is collected using a hydrophone. The transmitted sound field at this time is recorded as p0 (x, y, z = 0). The sound field on any plane is obtained using the angular spectrum method as P ’ (k x ,k y , z = l). Furthermore, we perform self-convolution on the acquired hydrophone signal to obtain the pulse-echo signal. We randomly switch 50 of these regions multiple times to transmit and use all of them for acquisition, then fill in the block matrix H in the linear system.

[0113] like Figure 9 , set up a simulated target area, then use the probe system to scan the target area, switch different areas to transmit multiple times and use all areas to receive echoes, and solve the linear equation to complete the target area image reconstruction. Figure 10 After multiple switching areas and acquisition, the peak signal-to-noise ratio of the detection imaging is 14.1282dB, which can clearly identify simulated defects. Dynamic 3D imaging can be completed by moving to other areas in real time.

[0114] The innovation of the present invention is:

[0115] 1) By dividing the acoustic radiation surface of the piezoelectric ceramic 5 into L×L electrode regions and employing a control circuit to independently control the excitation and reception of each electrode region, the acoustic radiation surface of the piezoelectric ceramic 5 and its control circuit differ from those of a phased array ultrasonic transducer. Unlike phased array ultrasonic transducers, this structure lacks complex logic circuitry and does not rely on electronic delays to control the excitation timing of each array element. Instead, the control circuit enables coordinated control of multiple array elements, such as one-shot all-receive and multiple-shot all-receive, through the electrode regions. This results in a simpler structure than existing 4D ultrasonic imaging systems.

[0116] 2) Currently, researchers increase additional signal measurement values by rotating or moving the mask. However, the present invention divides the spatial phase mask 7 into L×L mask areas, and each mask area has a different thickness. It is used in conjunction with the electrode area of the acoustic radiation surface of the piezoelectric ceramic 5. By randomly activating different areas each time, multiple groups of "multiple transmit and one receive" signals are collected, effectively solving the problem that it is difficult to rotate or move the mask to increase additional signal measurement values in the existing technology.

[0117] 3) The present invention proposes that the linear system model can be used to reconstruct the 4D ultrasonic image of the target area using the following formula: u=Hv+n. Compared with the existing method of reconstructing the 4D ultrasonic image of the target area, it is simpler and can clearly identify the simulated defects.

[0118] The present invention and its embodiments are described above. This description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs structures and embodiments similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A 4D ultrasonic imaging system based on partitioned electrodes and compressed sensing, for obtaining a four-dimensional ultrasonic image of a target area, characterized in that: it comprises a housing (1), a cable (3), a backing (4), a piezoelectric ceramic (5), a matching layer (6), a spatial phase mask (7) and a control circuit, wherein the backing (4), the piezoelectric ceramic (5) and the matching layer (6) are sequentially installed in the housing (1), the positive electrode surface of the piezoelectric ceramic (5) serves as an acoustic radiation surface and faces the target area, the negative electrode surface of the piezoelectric ceramic (5) is provided with a backing (4) for absorbing reflected waves, the piezoelectric ceramic (5) is electrically connected to the control circuit via a cable (3) passing through the housing (1), the spatial phase mask (7) is installed outside the housing (1) and contacts a side of the matching layer (6) away from the piezoelectric ceramic (5), and is used to modulate the spatial phase distribution of the transmitted acoustic wave; The sound radiation surface of the piezoelectric ceramic (5) is divided into L×L electrode areas, each electrode area is electrically connected to a control circuit, and the control circuit is used to control the independent excitation and reception of each electrode area. The negative electrode of the piezoelectric ceramic (5) is grounded.

2. The 4D ultrasound imaging system based on partitioned electrodes and compressed sensing according to claim 1, characterized in that: Also included is a compressed sensing linear module, the compressed sensing linear module being electrically connected to the control circuit and configured to reconstruct a 4D ultrasound image of the target area; It also includes a locking knob (2), which is arranged on the upper end surface of the housing (1) and is used to fix the cable (3) passing through the housing (1).

3. The 4D ultrasonic imaging system based on partitioned electrodes and compressed sensing according to claim 1, characterized in that: The size of the spatial phase mask (7) is the same as that of the piezoelectric ceramic (5), and the spatial phase mask (7) is divided into L×L mask areas, the thickness of each mask area is different, and the thickness relationship between the mask areas is set to meet the spatial phase difference between the transmitted waves of any two mask areas in the spatial phase mask (7) is greater than or equal to 0 and less than or equal to π, and the spatial phase difference between the transmitted waves of the two mask areas is set according to the following formula: φ=arg(P1-P2) Wherein, φ represents the spatial phase difference of the transmitted wave, arg() represents the complex argument, and P1 and P2 are the complex representations of the transmitted waves of the two mask areas respectively.

4. The 4D ultrasound imaging system based on partitioned electrodes and compressed sensing according to claim 1, characterized in that: The backing (4) and the matching layer (6) are both made of epoxy resin mixed with tungsten powder, the mass ratio of tungsten powder to epoxy resin in the backing (4) is (2-4):1, the mass ratio of tungsten powder to epoxy resin in the matching layer (6) is 1:(3-5), and the thickness of the matching layer (6) is equal to one-quarter of the central frequency wavelength of the piezoelectric ceramic (5).

5. The 4D ultrasonic imaging system based on partitioned electrodes and compressed sensing according to claim 1, characterized in that: The sound radiation surface of the piezoelectric ceramic (5) is divided into a plurality of electrode areas in any of the following ways: laser cutting, dicing cutting, or sputtering deposition of a metal electrode layer on the piezoelectric ceramic (5).

6. The 4D ultrasonic imaging system based on partitioned electrodes and compressed sensing according to claim 1, characterized in that: The sound radiation surface of the piezoelectric ceramic (5) is provided with a multi-electrode flexible circuit board or needle-shaped electrodes.

7. A 4D ultrasonic imaging method applied to a 4D ultrasonic imaging system based on partitioned electrodes and compressed sensing according to any one of claims 1 to 6, characterized in that: The steps include: S1. Scan the target area with wave fields to obtain the system matrix, and then establish a linear system model based on the system matrix; S2, randomly controlling the electrode area of the piezoelectric ceramic (5) so that the piezoelectric ceramic (5) emits ultrasonic waves, which are modulated by the spatial phase mask (7) and reflected by the target area to obtain an echo signal; S3, the echo signal passes through the spatial phase mask (7) and is received by the piezoelectric ceramic (5) to form a compressed signal, which is then recorded by the control circuit and transmitted to the linear system model; S4, repeating steps S2 and S3 multiple times and randomly controlling the electrode area of the piezoelectric ceramic (5) each time until the linear system model receives S compression signals, and reconstructing the linear system model according to the S compression signals to obtain a 4D ultrasound image of the target area.

8. The 4D ultrasonic imaging method according to claim 7, wherein: The wave field scanning is performed according to the following method: The ultrasonic wave modulated by the spatial phase mask (7) is collected by a hydrophone in a plane perpendicular to the propagation direction of the ultrasonic wave, and then the ultrasonic wave modulated by the spatial phase mask (7) is processed to obtain wave field data. Subsequently, the wave field data is propagated to planes with different propagation distances using an angular spectrum method to obtain wave field data with different propagation distances, and then a system matrix is constructed according to the wave field data with different propagation distances.

9. The 4D ultrasonic imaging method of claim 7, wherein: The linear system model reconstructs the 4D ultrasound image of the target area according to the following formula: u=Hv+n Where u represents the compressed signal, v represents the reconstructed 4D ultrasound image signal, n represents the noise signal, and H is the system matrix.

Images