Doppler imaging method and system based on multi-angle plane wave Hadamard coding

Abstract

The invention relates to the technical field of biomedical ultrasonic imaging, and discloses a Doppler imaging method and system based on multi-angle plane wave Hadamard coding, and the method comprises the steps: transmitting N groups of ultrasonic waves which are subjected to phase coding through Hadamard coding into a blood flow imaging region, each group of ultrasonic waves comprises N continuous plane waves which are different in angle and are separated by a preset time delay, N groups of ultrasonic echo signals are collected and decoded to obtain ultrasonic echo signals, and the step is repeatedly executed to obtain continuous multi-angle ultrasonic echo signals; moreover, according to the continuous multi-angle ultrasonic echo signals, an instantaneous blood flow image signal corresponding to the time window is obtained; a matrix equation set is constructed and solved to obtain the blood flow vectorization speed, a blood flow vector speed field transient image is generated, and / or a blood flow vector speed field dynamic change image is displayed. According to the method, the signal-to-noise ratio of plane wave imaging and the imaging sensitivity to weak blood flow signals can be remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of biomedical ultrasound imaging technology, and in particular to the technology of ultrasound blood flow velocity vector imaging. Background Art

[0002] Plane wave ultrafast ultrasound Doppler imaging technology has been widely used in the fields of blood flow imaging and tumor monitoring. Compared with traditional ultrasound, this technology has the advantages of being non-invasive, radiation-free, and having high spatiotemporal resolution, and can achieve high frame rate functional neuroimaging. Ultrafast ultrasound technology can achieve microvascular imaging with high spatiotemporal resolution, but traditional ultrafast ultrasound Doppler methods have angle-dependent limitations and can only determine the velocity component along the beam direction. Vector Doppler imaging technology estimates the Doppler velocity at different steering angles and combines it with high frame rate plane wave transmission to achieve angle-independent blood flow vector imaging.

[0003] However, the performance of vector Doppler imaging has not yet fully met the needs. For example, the imaging sensitivity of small blood vessels with low signal-to-noise ratio is poor, motion artifacts cannot be effectively reduced, and it is not practical. Therefore, its application in small blood vessel and microvascular imaging is limited. Summary of the invention

[0004] The purpose of the present application is to provide a Doppler imaging method and system based on multi-angle plane wave Hadamard coding to solve the problems raised in the above background technology.

[0005] The present application discloses a Doppler imaging method based on multi-angle plane wave Hadamard coding, comprising:

[0006] Step A: transmitting N groups of ultrasound waves phase-encoded using Hadamard coding into the blood flow imaging area, wherein each group of ultrasound waves includes N continuous plane waves with different angles and separated by a predetermined time delay, collecting N groups of ultrasound echo signals corresponding to the N groups of ultrasound waves and decoding them according to the Hadamard matrix to obtain ultrasound echo signals corresponding to the emission angles of the N plane waves, and repeatedly performing this step at a predetermined frequency to obtain continuous multi-angle ultrasound echo signals; and obtaining instantaneous blood flow image signals corresponding to the time window according to the continuous multi-angle ultrasound echo signals;

[0007] Step B: construct and solve a matrix equation group using the results of Doppler frequency estimation of the blood flow image signal, the blood flow velocity, and the emission angle of the plane wave to obtain the blood flow vector velocity, and generate a blood flow vector velocity field transient image and / or display a blood flow vector velocity field dynamic change image based on the blood flow vector velocity.

[0008] In a preferred embodiment, the step A further comprises the following sub-steps:

[0009] S1. The ultrasonic transducer transmits N groups of ultrasonic waves phase-encoded by Hadamard coding into the imaging area, wherein each group of ultrasonic waves comprises N continuous plane waves with different angles, and adjacent plane waves are separated by a predetermined time delay;

[0010] S2. The ultrasonic transducer receives the ultrasonic echo signal corresponding to each group of transmitted ultrasonic waves, and performs analog-to-digital conversion and sampling on the ultrasonic echo signal to obtain N groups of sampled ultrasonic echo signals;

[0011] S3, decoding and delay compensation of the sampled N groups of ultrasonic echo signals according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of N plane waves;

[0012] S4. Repeat the above steps at a fixed frequency to obtain continuous multi-angle ultrasonic echo signals corresponding to the ultrasonic waves phase-encoded by Hadamard encoding.

[0013] In a preferred embodiment, the step A further comprises the following sub-steps:

[0014] S5, performing beam synthesis and clutter filtering on the ultrasonic echo signal at each plane wave emission angle to obtain continuous multi-angle blood flow image signals;

[0015] S6. By setting a sliding time window, the long time sequence of the blood flow image signal is divided into continuous short sequences to obtain the instantaneous blood flow image signal corresponding to the time window.

[0016] In a preferred embodiment, the step B further comprises the following sub-steps:

[0017] S7, obtaining the Doppler axial velocity corresponding to each voxel of the blood flow at each plane wave emission angle by performing Doppler frequency estimation on the instantaneous blood flow image signal corresponding to each plane wave emission angle within the selected time window;

[0018] S8, constructing a matrix equation group between the blood flow velocity in a rectangular coordinate system, the emission angle of the plane wave, and the Doppler axial velocity corresponding to each voxel of the blood flow at each emission angle of the plane wave of the ultrasound;

[0019] S9. Obtain the blood flow vector velocity by solving the matrix equation group.

[0020] In a preferred embodiment, the step B further comprises the following sub-steps:

[0021] S11, generating a transient image of the blood flow vector velocity field at the current time on a display device according to the blood flow vector velocity; and / or,

[0022] S12. Displaying a dynamic change image of the blood flow vector velocity field by sliding a time window according to the blood flow vector velocity.

[0023] In a preferred embodiment, the step B further comprises the following sub-steps:

[0024] S10, performing interpolation and smoothing operations on the blood flow vector velocity.

[0025] In a preferred example, in the step S1, the transmission delay between the ultrasonic phased array channels is controlled to transmit plane waves at different angles.

[0026] In a preferred example, in the step S1, the type of ultrasonic wave emitted is a non-focused wave or a focused sound wave emitted in a synthetic aperture manner.

[0027] In a preferred example, in the S1 step, Hadamard coding refers to N-order Hadamard coding, where N is an integer between 2 and 256, and N, N / 12 or N / 20 must be an integer power of 2, and the pulses are encoded into positive pulses and negative pulses according to the values ​​of the Hadamard matrix.

[0028] In a preferred example, in the step S3, the collected N groups of continuous echo signals are linearly superimposed according to the value of each row in a given Hadamard matrix to achieve echo signal decoding.

[0029] In a preferred example, in step S3, the delay applied in step S1 is subtracted from each of N consecutive decoded echo signals to achieve delay compensation.

[0030] In a preferred embodiment, in step S4, the steps are repeated with a composite transmission frequency CPRF, wherein the Doppler velocity measurement range (-v max to v max ):

[0031]

[0032] Where c is the speed of sound in the tissue and f0 is the center frequency of ultrasound.

[0033] In a preferred example, in the step S5, the beamforming method is any one of the following: a delay-addition algorithm, a frequency-domain-beam-domain migration algorithm, an adaptive beamforming algorithm, and a spatial compounding method.

[0034] In a preferred example, in step S5, the method of clutter filtering is high-pass filtering or singular value decomposition.

[0035] In a preferred example, in step S7, the Doppler frequency estimation method is a delayed autocorrelation method.

[0036] In a preferred embodiment, in the steps S8-S9, when a one-dimensional probe is used to estimate the blood flow vector velocity in a two-dimensional plane, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each ultrasonic transmitting and receiving pair (the pth transmitting angle The qth receiving angle )have

[0037] Φ IR (p, q, x, z, t)=arg[IQ (p, q, x, z, t)*IQ * (p, q, x, z, tt PRF )] (2)

[0038] Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t PRF Indicates the transmission interval corresponding to the pulse repetition frequency PRF;

[0039] According to the geometric relationship, construct an NM×2 matrix K IR ,

[0040]

[0041] Among them, the subscripts x and z represent the components of the angle vector in the lateral direction and depth direction, N and M represent the number of transmitting and receiving angles, respectively, and the blood flow velocity vector is solved

[0042]

[0043] Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix, v x and v z They are the projections of blood flow velocity in the lateral direction and depth direction, respectively.

[0044] In a preferred embodiment, in the steps S8-S9, when a two-dimensional probe is used to estimate the blood flow vector velocity in three-dimensional space, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each ultrasonic transmitting and receiving pair (the pth transmitting angle The qth receiving angle )have

[0045] Φ IR(p, q, x, y, z, t)=arg[IQ (p, q, x, y, z, t)*IQ * (p, q, x, y, z, tt PRF )] (5)

[0046] Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t PRF Indicates the transmission interval corresponding to the pulse repetition frequency PRF;

[0047] According to the geometric relationship, construct a NM×3 matrix K IR ,

[0048]

[0049] Among them, the subscripts x and z represent the components of the angle vector in the lateral direction and depth direction, N and M represent the number of transmitting and receiving angles, respectively, and the blood flow velocity vector is solved

[0050]

[0051] Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix, V x , V y and V z They are the projections of blood flow velocity on the x, y and z axes of the three-dimensional coordinate system respectively.

[0052] In a preferred example, in the step S10, the interpolation method is any one of the following: nearest neighbor method, bilinear interpolation method, and multiple regression method.

[0053] In a preferred example, in the step S10, the smoothing operation is mean filtering or Gaussian filtering.

[0054] In a preferred embodiment, the method is used for any of the following blood flow imaging: blood flow in small blood vessels in the brain, spinal cord, kidney, liver, tumor, carotid artery, jugular vein, and intracardiac cavity of humans or animals.

[0055] The present application also discloses a Doppler imaging system based on multi-angle plane wave Hadamard coding, comprising:

[0056] A multi-angle ultrasonic echo signal and instantaneous blood flow image signal acquisition module is used to transmit N groups of ultrasonic waves phase-encoded using Hadamard coding into a blood flow imaging area, wherein each group of ultrasonic waves includes N continuous plane waves with different angles and separated by a predetermined time delay, collect N groups of ultrasonic echo signals corresponding to the N groups of ultrasonic waves and decode them according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of the N plane waves, and repeatedly perform this step at a predetermined frequency to obtain continuous multi-angle ultrasonic echo signals; and, based on the continuous multi-angle ultrasonic echo signals, obtain an instantaneous blood flow image signal corresponding to the time window;

[0057] The blood flow vector velocity field transient image and / or blood flow vector velocity field dynamically changing image generation module is used to construct and solve a matrix equation group using the results obtained by Doppler frequency estimation of the blood flow image signal, as well as the blood flow velocity and the emission angle of the plane wave to obtain the blood flow vectorization velocity, and generate a blood flow vector velocity field transient image and / or display a blood flow vector velocity field dynamically changing image based on the blood flow vectorization velocity.

[0058] The present application also discloses a Doppler imaging system based on multi-angle plane wave Hadamard coding, the system is used in any one of the above methods, wherein the system comprises:

[0059] An ultrasonic transducer, used for transmitting ultrasonic signals to the entire blood flow measurement area and receiving ultrasonic echo signals;

[0060] Multi-channel ultrasonic transmitting and receiving system, used to generate a specific pulse sequence to excite the ultrasonic transducer to transmit ultrasonic waves, sample and store ultrasonic echo signals;

[0061] A user operating system, used for the user to configure ultrasound emission and acquisition parameters and adjust signal processing parameters and steps;

[0062] Signal processing module, including pulse encoding and decoding module, image reconstruction module, orthogonal demodulation module, clutter filtering module, autocorrelation module, and velocity vector solution module;

[0063] The image display device is used to display a user operation interface, a transient image of a blood flow vector velocity field, and / or a dynamic change image of a blood flow vector velocity field.

[0064] The present application adopts multi-angle plane wave emission technology and Hadamard coding, which not only significantly improves the signal-to-noise ratio of plane wave imaging, but also significantly improves the imaging sensitivity to weak blood flow signals, thereby improving the accuracy of blood flow velocity measurement in small blood vessels with slow flow velocity and small size. Furthermore, the present application can obtain blood flow images at multiple different angles at the same time by using Hadamard for phase encoding and decoding, thereby effectively reducing artifacts caused by motion. Furthermore, the present application can conveniently and efficiently realize direct measurement of blood flow vector velocity by estimating the Doppler frequency of blood flow image signals, establishing and solving a group of matrix equations. Furthermore, the present application can generate transient images of blood flow vector velocity fields and display the dynamic changes of blood flow vector velocity fields in real time, which is helpful for analyzing hemodynamic characteristics and providing analysis data for potential vascular diseases, including abnormal blood flow velocity, vascular blockage, vascular stenosis, vascular embolism, etc.

[0065] A large number of technical features are recorded in the specification of this application, which are distributed in various technical solutions. If all possible combinations of technical features of this application (i.e., technical solutions) are to be listed, the specification will be too long. In order to avoid this problem, the various technical features disclosed in the above-mentioned invention content of this application, the various technical features disclosed in the various embodiments and examples below, and the various technical features disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions are all deemed to have been recorded in this specification), unless the combination of such technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed, and features C and D are equivalent technical means that play the same role. Technically, only one can be used, and it is impossible to use them at the same time. Feature E can be combined with feature C technically. Then, the solution of A+B+C+D should not be deemed to have been recorded because it is technically infeasible, and the solution of A+B+C+E should be deemed to have been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 is a flow chart of an ultrasonic vector Doppler imaging method based on multi-angle plane wave Hadamard coded excitation according to an embodiment of the present invention;

[0067] Figure 2 It is an ultrasonic wave after 4th-order Hadamard phase encoding in an ultrasonic vector Doppler imaging method based on multi-angle plane wave Hadamard coded excitation according to an embodiment of the present invention;

[0068] Figure 3 It is a rat brain B-ultrasound image and a blood flow image after clutter filtering in an ultrasonic vector Doppler imaging method based on multi-angle plane wave Hadamard coded excitation according to an embodiment of the present invention;

[0069] Figure 4 A two-dimensional vector Doppler image of rat cerebral blood flow in an ultrasonic vector Doppler imaging method based on multi-angle plane wave Hadamard coded excitation according to an embodiment of the present invention;

[0070] Figure 5 It is a comparative embodiment of the present invention, which uses a non-coding method to obtain a rat brain B-ultrasound image and a blood flow image after clutter filtering;

[0071] Figure 6 It is a comparative embodiment of the present invention, which uses a non-coding method to obtain a two-dimensional vector Doppler image of rat cerebral blood flow;

[0072] Figure 7 Detailed Description of the Invention The present invention is another flowchart of an ultrasonic vector Doppler imaging method based on multi-angle plane wave Hadamard coded excitation according to an embodiment of the present invention.

[0073] Figure 8 4 is a schematic structural diagram of an ultrasonic vector Doppler imaging system based on multi-angle plane wave Hadamard coded excitation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0074] In the following description, many technical details are provided to help readers better understand the present application. However, those skilled in the art can understand that the technical solution claimed in the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0075] Description of some concepts:

[0076] Multi-angle plane wave is a term used in ultrasound imaging technology, which is mainly used to improve the quality and performance of ultrasound imaging. In this technology, the ultrasound probe transmits multiple different plane waves, each with a different propagation direction or angle. By synthesizing the echo signals of these plane waves, multi-angle imaging of the target area can be achieved.

[0077] Hadamard coding is a coding method based on the Hadamard Matrix, which is mainly used in the fields of communication, signal processing and image processing. The Hadamard matrix is ​​a special orthogonal matrix whose elements only contain +1 and -1, and the product of the matrix and its transposed matrix is ​​equal to the matrix order multiplied by the unit matrix.

[0078] The blood flow vector velocity field transient image is an image used to represent blood flow velocity vector information in ultrasound imaging technology. This image reflects the distribution of blood flow velocity and its direction in a blood vessel at a specific moment. In the blood flow vector velocity field transient image, each pixel usually contains two main pieces of information: velocity magnitude and direction.

[0079] The following is a brief description of some of the innovative features of this application:

[0080] After years of research, the inventor of this application found that the vector Doppler imaging in the prior art has poor imaging sensitivity for small blood vessels with low signal-to-noise ratio, and thus its application in small blood vessel and microvascular imaging is limited, mainly due to the lack of focusing and multi-angle echo coherence compounding, resulting in poor imaging sensitivity for small blood vessels with low signal-to-noise ratio. Therefore, a Doppler imaging technology based on multi-angle plane wave Hadamard coding is creatively proposed, which combines ultrafast ultrasound imaging technology, multi-angle plane wave coding excitation technology and vector Doppler imaging technology, and provides an ultrasound vector Doppler imaging method based on multi-angle plane wave Hadamard coding excitation, which improves the spatiotemporal resolution of current ultrasound vector Doppler imaging and the sensitivity to small blood flow imaging.

[0081] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0082] The first embodiment of the present application relates to a Doppler imaging method based on multi-angle plane wave Hadamard coding, and the process is as follows: Figure 1 and Figure 7 As shown, the method comprises the following steps:

[0083] Step A: transmitting N groups of ultrasound waves phase-encoded using Hadamard coding into the blood flow imaging area, wherein each group of ultrasound waves includes N continuous plane waves with different angles and separated by a predetermined time delay, collecting N groups of ultrasound echo signals corresponding to the N groups of ultrasound waves and decoding them according to the Hadamard matrix to obtain ultrasound echo signals corresponding to the emission angles of the N plane waves, and repeatedly performing this step at a predetermined frequency to obtain continuous multi-angle ultrasound echo signals; and obtaining an instantaneous blood flow image signal corresponding to the time window according to the continuous multi-angle ultrasound echo signals;

[0084] Optionally, step A further comprises the following sub-steps:

[0085] S1. The ultrasonic transducer transmits N groups of ultrasonic waves phase-encoded by Hadamard coding into the imaging area, wherein each group of ultrasonic waves comprises N continuous plane waves with different angles, and adjacent plane waves are separated by a predetermined time delay;

[0086] S2. The ultrasonic transducer receives the ultrasonic echo signal corresponding to each group of transmitted ultrasonic waves, and performs analog-to-digital conversion and sampling on the ultrasonic echo signal to obtain N groups of sampled ultrasonic echo signals;

[0087] S3, decoding and delay compensation of the sampled N groups of ultrasonic echo signals according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of N plane waves;

[0088] S4, repeating the above steps at a fixed frequency to obtain a continuous multi-angle ultrasonic echo signal corresponding to the ultrasonic wave phase-encoded by Hadamard encoding;

[0089] S5, performing beam synthesis and clutter filtering on the ultrasonic echo signal at each plane wave emission angle to obtain continuous multi-angle blood flow image signals;

[0090] S6. By setting a sliding time window, the long time sequence of the blood flow image signal is divided into continuous short sequences to obtain the instantaneous blood flow image signal corresponding to the time window.

[0091] Step B: construct and solve a matrix equation group using the results of Doppler frequency estimation of the blood flow image signal, the blood flow velocity, and the emission angle of the plane wave to obtain the blood flow vector velocity, and generate a blood flow vector velocity field transient image and / or display a blood flow vector velocity field dynamic change image based on the blood flow vector velocity.

[0092] S7, obtaining the Doppler axial velocity corresponding to each voxel of the blood flow at each plane wave emission angle by performing Doppler frequency estimation on the instantaneous blood flow image signal corresponding to each plane wave emission angle within the selected time window;

[0093] S8, constructing a matrix equation group between the blood flow velocity in a rectangular coordinate system, the emission angle of the plane wave, and the Doppler axial velocity corresponding to each voxel of the blood flow at each emission angle of the plane wave of the ultrasound;

[0094] S9, obtaining the blood flow vector velocity by solving the matrix equation group;

[0095] S10, performing interpolation and smoothing operations on the blood flow vector velocity;

[0096] S11, generating a transient image of the blood flow vector velocity field at the current time on a display device according to the blood flow vector velocity; and / or,

[0097] S12. Displaying a dynamic change image of the blood flow vector velocity field by sliding a time window according to the blood flow vector velocity.

[0098] Optionally, in step S1, the emission delay between channels of the ultrasonic phased array is controlled to achieve emission of plane waves at different angles.

[0099] Optionally, in the step S1, the type of ultrasonic wave emitted is a non-focused wave or a focused sound wave emitted in a synthetic aperture manner.

[0100] Optionally, in step S1, Hadamard coding refers to N-order Hadamard coding, where N is an integer between 2 and 256, and N, N / 12 or N / 20 must be an integer power of 2, and the pulses are encoded into positive pulses and negative pulses according to the values ​​of the Hadamard matrix.

[0101] Optionally, in the step S3, the collected N groups of continuous echo signals are linearly superimposed according to the value of each row in the given Hadamard matrix to achieve echo signal decoding.

[0102] Optionally, in step S3, the delay applied in step S1 is subtracted from each of N consecutive decoded echo signals to achieve delay compensation.

[0103] Optionally, in step S4, the steps are repeated with a composite transmission frequency CPRF, wherein the Doppler velocity measurement range (-v max to v max ):

[0104]

[0105] Where c is the speed of sound in the tissue and f0 is the center frequency of ultrasound.

[0106] Optionally, in the step S5, the beamforming method is any one of the following: a delay superposition algorithm, a frequency domain-beam domain migration algorithm, an adaptive beamforming algorithm, and a spatial compounding method.

[0107] Optionally, in step S5, the method of clutter filtering is high-pass filtering or singular value decomposition.

[0108] Optionally, in step S7, the Doppler frequency estimation method is a delayed autocorrelation method.

[0109] Optionally, in the steps S8-S9, when a one-dimensional probe is used to estimate the blood flow vector velocity in a two-dimensional plane, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each ultrasonic transmitting and receiving pair (the pth transmitting angle The qth receiving angle )have

[0110] Φ IR(p, q, x, z, t)=arg[IQ (p, q, x, z, t)*IQ * (p, q, x, z, tt PRF )] (2)

[0111] Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t PRF Indicates the transmission interval corresponding to the pulse repetition frequency PRF;

[0112] According to the geometric relationship, construct an NM×2 matrix K IR ,

[0113]

[0114] Among them, the subscripts x and z represent the components of the angle vector in the lateral direction and depth direction, N and M represent the number of transmitting and receiving angles, respectively, and the blood flow velocity vector is solved

[0115]

[0116] Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix, v x and v z They are the projections of blood flow velocity in the lateral direction and depth direction, respectively.

[0117] Optionally, in the steps S8-S9, when a two-dimensional probe is used to estimate the blood flow vector velocity in three-dimensional space, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each ultrasonic transmitting and receiving pair (the pth transmitting angle The qth receiving angle )have

[0118] Φ IR (p, q, x, y, z, t)=arg[IQ (p, q, x, y, z, t)*IQ * (p, q, x, y, z, tt PRF )] (5)

[0119] Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t PRF Indicates the transmission interval corresponding to the pulse repetition frequency PRF;

[0120] According to the geometric relationship, construct a NM×3 matrix K IR ,

[0121]

[0122] Among them, the subscripts x and z represent the components of the angle vector in the lateral direction and depth direction, N and M represent the number of transmitting and receiving angles, respectively, and the blood flow velocity vector is solved

[0123]

[0124] Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix, V x , V y and V z They are the projections of blood flow velocity on the x, y and z axes of the three-dimensional coordinate system respectively.

[0125] Optionally, in step S10, the interpolation method is any one of the following: nearest neighbor method, bilinear interpolation method, and multiple regression method.

[0126] Optionally, in step S10, the smoothing operation is mean filtering or Gaussian filtering.

[0127] Optionally, the method is used for blood flow imaging of any of the following: blood flow in small blood vessels in the brain, spinal cord, kidney, liver, tumor, carotid artery, jugular vein, and intracardiac cavity of humans or animals.

[0128] In order to better understand the technical solution of the present application, a specific example is provided below for illustration. The details listed in the example are mainly for ease of understanding and are not intended to limit the scope of protection of the present application.

[0129] In this example, the Doppler imaging method based on multi-angle plane wave Hadamard coding includes the following steps:

[0130] S1. The ultrasonic transducer transmits N groups of ultrasonic waves that are phase-encoded by Hadamard coding into the blood flow imaging area, wherein each group of ultrasonic waves includes N continuous plane waves with different angles, and adjacent plane waves are separated by a predetermined time delay.

[0131] Among them, plane wave means that the ultrasonic probe applies the same delay or linearly increasing delay to all transducer units to transmit pulses, so that the wavefront is a plane. N consecutive plane waves with different angles means that after the ultrasonic probe transmits an inclined plane wave, before receiving the echo signal, it transmits inclined plane waves multiple times, and transmits a total of N plane waves with different angles. The time interval between two transmissions is generally between a few nanoseconds and tens of nanoseconds.

[0132] S2. The ultrasonic transducer receives the ultrasonic echo signal corresponding to each group of transmitted ultrasonic waves, and performs analog-to-digital conversion and sampling on the ultrasonic echo signal to obtain N groups of sampled ultrasonic echo signals.

[0133] In this step, the ultrasonic transducer receives a group of ultrasonic echo signals, a total of N groups of ultrasonic echo signals, and performs analog-to-digital conversion and sampling.

[0134] S3. Decode and delay-compensate the sampled N groups of ultrasonic echo signals according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of N plane waves.

[0135] Optionally, in step S3, the collected N groups of continuous echo signals are linearly superimposed according to the value of each row in a given Hadamard matrix to achieve echo signal decoding.

[0136] Optionally, in step S3, the delay applied in step S1 is subtracted from each of N consecutive decoded echo signals to achieve delay compensation.

[0137] S4. Repeat the above steps at a fixed frequency to obtain continuous multi-angle ultrasonic echo signals corresponding to the ultrasonic waves phase-encoded by Hadamard encoding.

[0138] Specifically, each time the above steps are repeated, N multi-angle echo signals can be obtained. Continuous multi-angle echo signals refer to a series of multi-angle echo signals obtained after quickly repeating the above steps.

[0139] It should be noted that in other embodiments of the present invention, discontinuous multi-angle echo signals may also be obtained according to actual needs.

[0140] Optionally, in step S4, the repetition frequency is called the composite transmission frequency (CPRF), which determines the Doppler velocity measurement range of a single angle (-v max to v max ):

[0141]

[0142] Where c is the speed of sound in the tissue and f0 is the center frequency of ultrasound.

[0143] S5. Obtain continuous multi-angle blood flow image signals by performing beam synthesis and clutter filtering on the ultrasonic echo signals at each plane wave emission angle.

[0144] Among them, beam synthesis and clutter filtering are performed on the ultrasonic echo signal at each angle respectively to filter out tissue signals and part of the noise signals.

[0145] Optionally, in the step S5, the beamforming method is not limited, including but not limited to the commonly used delay superposition algorithm, frequency domain-beam domain migration algorithm, adaptive beamforming algorithm, spatial compounding method, etc.

[0146] Optionally, in step S5, the method for clutter filtering is not limited, including but not limited to commonly used high-pass filtering, singular value decomposition, etc.

[0147] S6, by setting a sliding time window, dividing the long time sequence of the blood flow image signal into continuous short sequences, so as to obtain an instantaneous blood flow image signal corresponding to the time window, and the corresponding instantaneous blood flow image signal is used to analyze the dynamic change of blood flow;

[0148] S7. By estimating the Doppler frequency of the instantaneous blood flow image signal corresponding to the emission angle of each plane wave within the selected time window, the corresponding Doppler axial velocity of each voxel of the blood flow at each plane wave emission angle is obtained.

[0149] Optionally, in step S7, the Doppler frequency estimation method includes but is not limited to a delayed autocorrelation method.

[0150] S8. Construct a matrix equation group between the blood flow velocity in a rectangular coordinate system, the emission angle of the plane wave, and the Doppler axial velocity corresponding to each voxel of the blood flow at each emission angle of the plane wave of the ultrasound.

[0151] S9. Obtain the blood flow vector velocity by solving the matrix equation group.

[0152] S10, performing interpolation and smoothing operations on the blood flow vector velocity;

[0153] Optionally, in other embodiments of the present invention, the obtained vectorized velocity may also be subjected to anti-aliasing. According to Shannon sampling theorem, the sampling frequency must be no less than twice the signal frequency, otherwise spectral aliasing will occur. The greater the blood flow velocity, the greater the corresponding Doppler frequency. When the Doppler frequency is greater than CPRF / 2, spectral aliasing will occur, which will cause errors in the estimation of blood flow velocity and direction. Based on deep learning, multiple pulse transmission frequencies, least squares linear regression, and other anti-aliasing techniques have been developed to estimate higher blood flow velocities with lower pulse transmission frequencies.

[0154] Optionally, in the step S10, the interpolation step is a non-essential step, and the interpolation method is not limited. Common interpolation methods include the nearest neighbor method, the bilinear interpolation method, the multivariate regression method, and the like.

[0155] Optionally, in the step S10, the smoothing step is a non-essential step, and the smoothing method is not limited. Common smoothing methods include mean filtering, Gaussian filtering, and the like.

[0156] S11-S12, generating a transient image of the blood flow vector velocity field at the current time according to the blood flow vector velocity, and / or displaying a dynamic change image of the blood flow vector velocity field. Specifically:

[0157] S11. Generate a transient image of the blood flow vector velocity field at the current time on a display device according to the blood flow vector velocity.

[0158] S12. Displaying a dynamic change image of the blood flow vector velocity field by sliding a time window according to the blood flow vector velocity.

[0159] It should be noted that the imaging objects in the above embodiments include but are not limited to the blood flow in small blood vessels in the brain, spinal cord, kidney, liver, and tumor of humans and animals, as well as the blood flow in large blood vessels such as the carotid artery, jugular vein, and intracardiac cavity.

[0160] Optionally, in other embodiments of the present invention, the order of the above steps can be changed or adjusted as needed, which will not be described in detail here.

[0161] In this example, the transmission delay between the ultrasonic phased array channels is set to transmit plane waves at different angles.

[0162] In this example, the number of groups of transmitted ultrasonic waves is the same as the number of plane waves contained in each group of ultrasonic waves, both of which are denoted as N.

[0163] Optionally, in step S1, the type of sound waves emitted may also be non-focused waves such as divergent waves, or focused sound waves emitted in a synthetic aperture manner.

[0164] In this example, in step 1, the pulse encoding method is N-order Hadamard encoding, N is an integer, and N, N / 12 or N / 20 must be an integer power of 2. The ultrasonic pulse is encoded into a positive pulse and a negative pulse according to the value of the Hadamard matrix.

[0165] It should be noted that in the present invention, the range of N is 2-256. In some embodiments of the present invention, the range of N may be 4-32. Preferably, the range of N may be 4-16.

[0166] Through the Doppler imaging method based on multi-angle plane wave Hadamard coding in this example, pulse coding excitation can enhance the image signal-to-noise ratio. Assuming that the background noise is electronic white noise, the time standard deviation of each pixel in the image obtained by N-order Hadamard coding should be divided by According to the energy calculation, the signal-to-noise ratio gain is 10log 10 (N)dB.

[0167] More specifically, the above-mentioned embodiments can achieve a significant technical effect, namely, enhancing the contrast of the image, especially in deep tissues. Due to the attenuation of ultrasonic energy, the blood flow signal in the deep tissues may be submerged in the background noise. The above-mentioned embodiments can enhance the depth of imaging.

[0168] The Doppler imaging method based on multi-angle plane wave Hadamard coding in this example is applicable to blood flow vector imaging in two-dimensional plane and three-dimensional space.

[0169] Specifically, in one example, a linear array probe is used to perform two-dimensional plane blood flow vector imaging. In the steps S8 to S9, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each transmit-receive pair (the pth transmit angle The qth receiving angle )have

[0170] Φ IR (p, q, x, z, t)=arg[IQ (p, q, x, z, t)*IQ * (p, q, x, z, tt CPRF )] (1)

[0171] Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t CPRF Indicates the transmission interval corresponding to the composite transmission frequency CPRF.

[0172] According to the geometric relationship, construct an NM×2 matrix K IR ,

[0173]

[0174] The indices x and z represent the lateral and depth components of the angle vector, and N and M represent the number of transmit and receive angles, respectively. Solving for the velocity vector

[0175]

[0176] Among them, p inv (K IR )=(K T IRK IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix, v x and v z They are the projections of blood flow velocity in the lateral direction and depth direction, respectively.

[0177] Specifically, in another example, a two-dimensional probe is used to perform three-dimensional blood flow vector imaging. In the steps S8 to S9, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each transmit-receive pair (the pth transmit angle The qth receiving angle )have

[0178] Φ IR (p, q, x, y, z, t)=arg[IQ (p, q, x, y, z, t)*IQ * (p, q, x, y, z, tt CPRF )] (4)

[0179] Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t CPRF Indicates the transmission interval corresponding to the composite transmission frequency CPRF.

[0180] According to the geometric relationship, construct a NM×3 matrix K IR ,

[0181]

[0182] The indices x and z represent the lateral and depth components of the angle vector, and N and M represent the number of transmit and receive angles, respectively. Solving for the velocity vector

[0183]

[0184] Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix, v x , v y and v z They are the projections of blood flow velocity on the x, y and z axes of the three-dimensional coordinate system respectively.

[0185] In order to make the Doppler imaging method based on multi-angle plane wave Hadamard coding in this example easier to understand, the following Figure 1 Provide detailed explanation.

[0186] like Figure 1 As shown, the Doppler imaging method based on multi-angle plane wave Hadamard coding includes the following process:

[0187] (1) Ultrasonic multi-angle plane wave pulse coding

[0188] A linear array transducer is used to realize plane waves with different tilt angles by setting the delay between channels. In this example, four tilt plane waves with different angles (θ1~θ4) are set. Each group of transmission contains the above four plane waves with different angles. The plane waves are superimposed with a certain delay (τ1~τ4) to avoid overlapping. The polarity of the plane wave is determined by the value in the 4th-order Hadamard matrix, where +1 represents a positive pulse and -1 represents a negative pulse. The four groups of encoded signals have the same transmission mode, and the only difference is the polarity of the included plane waves, as shown in the attached figure. Figure 2 As shown, the red line represents the half wavelength with a positive amplitude, the black line represents the half wavelength with a negative amplitude, and each pulse in the figure contains two wavelengths. The four groups of plane waves emitted for the first time are (+θ1, +θ2, +θ3, +θ4), the four groups of plane waves emitted for the second time are (+θ1, -θ2, +θ3, -θ4), the four groups of plane waves emitted for the third time are (+θ1, +θ2, -θ3, -θ4), and the four groups of plane waves emitted for the fourth time are (+θ1, -θ2, -θ3, +θ4).

[0189] (2) Ultrasonic signal transmission and reception

[0190] The 4 groups of encoded pulse waves are transmitted according to the set pulse transmission frequency, and the echo signal is received and stored after each pulse transmission. The transmission and reception of the 4 groups of pulse signals are repeated according to the set composite transmission frequency.

[0191] (3) Echo data decoding

[0192] The four groups of echo signals are multiplied by the column vector of the fourth-order Hadamard matrix respectively, and then linearly superimposed according to the rows. The delay compensation is then performed on the signals after row superposition, that is, the delays τ1~τ4 set during encoding are subtracted respectively, and the ultrasonic echo signals under the plane waves with tilt angles of θ1~θ4 corresponding to them can be decoded.

[0193] (3) Beamforming and clutter filtering

[0194] The decoded ultrasonic echo signals at multiple angles are independently beamformed and clutter filtered according to the same method and parameters. The clutter filtering step filters out the tissue signals from slow motion in the echoes to obtain multi-angle echo signals of dynamic blood flow.

[0195] (4) Doppler frequency estimation

[0196] Set the sliding time window, perform short-time autocorrelation analysis on the image time series obtained from each angle, and calculate the Doppler velocity of each voxel at each emission angle, as shown in the following formula:

[0197]

[0198]

[0199] Among them, S fIQ{i} represents the blood flow echo signal of the i-th transmission angle, f0 is the center frequency, CPRF is the composite transmission frequency, R1 is the autocorrelation sequence of the filtered signal with a delay of 1, and Nt is the size of the selected time window.

[0200] (5) Vector velocity solution

[0201] The blood flow velocity vector in the two-dimensional plane Decomposed into the transverse vector v x and the axial vector v z According to the geometric relationship, construct a NM×2 matrix K IR ,

[0202]

[0203] The indices x and z represent the components of the angle vector in the lateral and depth directions, and N and M represent the number of transmitting and receiving angles, respectively. In this diagram, N = 4, M = 1,

[0204]

[0205] According to K IR v=u, we can get:

[0206]

[0207] Solve the vector velocity according to the following formula:

[0208]

[0209] Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , indicating K IR The pseudo-inverse matrix of .

[0210] (6) Interpolation and smoothing

[0211] In order to improve the display effect, interpolation and smoothing operations are performed. Those skilled in the art can select appropriate interpolation and smoothing methods.

[0212] (7) Blood flow velocity vector display

[0213] According to each pixel (v x , v z ), draw a two-dimensional vector Doppler velocity image, and use arrows to simulate vectorized velocity, where the arrow length or arrow color can represent the magnitude of the velocity, and the arrow direction represents the direction of the velocity.

[0214] The above examples can be applied to rotating phantoms, blood flow vector imaging of small vascular systems in the brain and spinal cord.

[0215] The imaging results of the above example are shown below in conjunction with the accompanying figure of rat cerebral blood flow imaging.

[0216] Attached Figure 3 a is a single-frame B-ultrasound image of the rat brain coronal plane after beam synthesis. Figure 3 b is a single-frame blood flow image after clutter filtering.

[0217] Attached Figure 4 a is the blood flow vector imaging result of the whole brain coronal plane of rats. Figure 4 The areas within the white and green boxes in a are enlarged and shown as follows: Figure 4 b and 4c.

[0218] For comparison, Figure 5 a is a single-frame B-ultrasound image of the whole rat brain coronal plane after beam synthesis obtained by conventional multi-angle plane wave imaging without Hadamard coding. Figure 5 b is a single-frame blood flow image after clutter filtering. Figure 5 The signal-to-noise ratio of a is significantly lower than Figure 3 a, Figure 5 The blood flow signal in b is obviously weaker than that in Figure 3 b.

[0219] Attached Figure 6 a is the blood flow vector imaging result of the whole brain coronal plane of rats obtained by conventional multi-angle plane wave vector Doppler imaging without Hadamard encoding. Figure 6 The areas within the white and green boxes in a are enlarged and shown as follows: Figure 6 b and 6c. Figure 6 a, b, c and Figure 4 Compared with a, b, and c, some low-speed blood flow images are missing, and the blood flow vectorization results are more chaotic.

[0220] The Doppler imaging method based on multi-angle plane wave Hadamard coding in the above example can be implemented by the following Doppler imaging system based on multi-angle plane wave Hadamard coding, which includes:

[0221] An ultrasonic transducer, used for transmitting ultrasonic signals to the entire blood flow measurement area and receiving ultrasonic echo signals;

[0222] Multi-channel ultrasonic transmitting and receiving system, used to generate a specific pulse sequence to excite the ultrasonic transducer to transmit ultrasonic waves, sample and store ultrasonic echo signals;

[0223] A user operating system, used for the user to configure ultrasound emission and acquisition parameters and adjust signal processing parameters and steps;

[0224] Signal processing module, including pulse encoding and decoding module, image reconstruction module, orthogonal demodulation module, clutter filtering module, autocorrelation module, and velocity vector solution module;

[0225] The image display device is used to display a user operation interface, a transient image of a blood flow vector velocity field, and / or a dynamic change image of a blood flow vector velocity field.

[0226] Technical effect:

[0227] 1) Compared with traditional ultrasound color Doppler imaging technology, it can visualize the velocity magnitude and direction of each voxel, provide more detailed hemodynamic information and complex blood flow patterns, and can be further used in clinical medical problems such as vascular disease diagnosis.

[0228] 2) By combining ultrafast ultrasound imaging technology and multi-angle plane wave coded excitation technology, the imaging signal-to-noise ratio is significantly improved, and the sensitivity of small blood flow imaging is enhanced, which has significant clinical application in small blood vessel systems such as the brain and spinal cord.

[0229] The second embodiment of the present application relates to a Doppler imaging system based on multi-angle plane wave Hadamard coding, and its structure is as follows: Figure 8 As shown, the Doppler imaging system based on multi-angle plane wave Hadamard coding includes:

[0230] A multi-angle ultrasonic echo signal and instantaneous blood flow image signal acquisition module is used to transmit N groups of ultrasonic waves phase-encoded using Hadamard coding into a blood flow imaging area, wherein each group of ultrasonic waves includes N continuous plane waves with different angles and separated by a predetermined time delay, collect N groups of ultrasonic echo signals corresponding to the N groups of ultrasonic waves and decode them according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of the N plane waves, and repeatedly perform this step at a predetermined frequency to obtain continuous multi-angle ultrasonic echo signals; and, based on the continuous multi-angle ultrasonic echo signals, obtain an instantaneous blood flow image signal corresponding to the time window;

[0231] The blood flow vector velocity field transient image and / or blood flow vector velocity field dynamically changing image generation module is used to construct and solve a matrix equation group using the results obtained by Doppler frequency estimation of the blood flow image signal, as well as the blood flow velocity and the emission angle of the plane wave to obtain the blood flow vectorization velocity, and generate a blood flow vector velocity field transient image and / or display a blood flow vector velocity field dynamically changing image based on the blood flow vectorization velocity.

[0232] The first implementation manner is a method implementation manner corresponding to the present implementation manner. The technical details in the first implementation manner can be applied to the present implementation manner, and the technical details in the present implementation manner can also be applied to the first implementation manner.

[0233] It should be noted that those skilled in the art should understand that the implementation functions of each module shown in the implementation of the Doppler imaging system based on multi-angle plane wave Hadamard coding can be understood by referring to the relevant description of the Doppler imaging method based on multi-angle plane wave Hadamard coding. The functions of each module shown in the implementation of the Doppler imaging system based on multi-angle plane wave Hadamard coding can be implemented by a program (executable instruction) running on a processor, or by a specific logic circuit. If the Doppler imaging system based on multi-angle plane wave Hadamard coding in the embodiment of the present application is implemented in the form of a software function module and sold or used as an independent product, it can also be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the embodiment of the present application can be essentially or partly reflected in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the methods described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read Only Memory), disk or optical disk and other media that can store program codes. Thus, embodiments of the present application are not limited to any specific combination of hardware and software.

[0234] Accordingly, an embodiment of the present application further provides a computer storage medium, in which computer executable instructions are stored. When the computer executable instructions are executed by a processor, the various method embodiments of the present application are implemented.

[0235] In addition, the embodiment of the present application also provides a Doppler imaging system based on multi-angle plane wave Hadamard coding, which includes a memory for storing computer executable instructions, and a processor; the processor is used to implement the steps in the above-mentioned method implementation when executing the computer executable instructions in the memory. Among them, the processor can be a central processing unit (Central Processing Unit, referred to as "CPU"), or other general-purpose processors, digital signal processors (Digital Signal Processor, referred to as "DSP"), Application Specific Integrated Circuit (Application Specific Integrated Circuit, referred to as "ASIC"), etc. The aforementioned memory can be a read-only memory (read-only memory, referred to as "ROM"), a random access memory (random access memory, referred to as "RAM"), a flash memory (Flash), a hard disk or a solid-state hard disk, etc. The steps of the method disclosed in each embodiment of the present invention can be directly embodied as being executed by a hardware processor, or executed by a combination of hardware and software modules in the processor.

[0236] It should be noted that in the application documents of this patent, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including one" do not exclude the existence of other identical elements in the process, method, article or device including the elements. In the application documents of this patent, if it is mentioned that an action is performed according to an element, it means that the action is performed at least according to the element, which includes two situations: performing the action only according to the element, and performing the action according to the element and other elements. Expressions such as multiple, multiple, and multiple include 2, 2 times, 2 kinds, and more than 2, more than 2 times, and more than 2 kinds.

[0237] All documents mentioned in this application are considered to be included in the disclosure of this application as a whole, so that they can be used as the basis for modification when necessary. In addition, it should be understood that after reading the above disclosure of this application, those skilled in the art can make various changes or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. A Doppler imaging method based on multi-angle plane wave Hadamard coding, characterized in that: include: Step A: transmitting N groups of ultrasound waves phase-encoded using Hadamard coding into the blood flow imaging area, wherein each group of ultrasound waves includes N continuous plane waves with different angles and separated by a predetermined time delay, collecting N groups of ultrasound echo signals corresponding to the N groups of ultrasound waves and decoding them according to the Hadamard matrix to obtain ultrasound echo signals corresponding to the emission angles of the N plane waves, and repeatedly performing this step at a predetermined frequency to obtain continuous multi-angle ultrasound echo signals; and obtaining instantaneous blood flow image signals corresponding to the time window according to the continuous multi-angle ultrasound echo signals; Step B: construct and solve a matrix equation group using the results of Doppler frequency estimation of the blood flow image signal, the blood flow velocity, and the emission angle of the plane wave to obtain the blood flow vector velocity, and generate a blood flow vector velocity field transient image and / or display a blood flow vector velocity field dynamic change image based on the blood flow vector velocity.

2. The method according to claim 1, characterized in that The step A further comprises the following sub-steps: S1. The ultrasonic transducer transmits N groups of ultrasonic waves phase-encoded by Hadamard coding into the imaging area, wherein each group of ultrasonic waves comprises N continuous plane waves with different angles, and adjacent plane waves are separated by a predetermined time delay; S2. The ultrasonic transducer receives the ultrasonic echo signal corresponding to each group of transmitted ultrasonic waves, and performs analog-to-digital conversion and sampling on the ultrasonic echo signal to obtain N groups of sampled ultrasonic echo signals; S3, decoding and delay compensation of the sampled N groups of ultrasonic echo signals according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of N plane waves; S4. Repeat the above steps at a fixed frequency to obtain continuous multi-angle ultrasonic echo signals corresponding to the ultrasonic waves phase-encoded by Hadamard encoding.

3. The method according to claim 2, characterized in that The step A further comprises the following sub-steps: S5, performing beam synthesis and clutter filtering on the ultrasonic echo signal at each plane wave emission angle to obtain continuous multi-angle blood flow image signals; S6. By setting a sliding time window, the long time sequence of the blood flow image signal is divided into continuous short sequences to obtain the instantaneous blood flow image signal corresponding to the time window.

4. The method according to claim 3, characterized in that The step B further comprises the following sub-steps: S7, obtaining the Doppler axial velocity corresponding to each voxel of the blood flow at each plane wave emission angle by performing Doppler frequency estimation on the instantaneous blood flow image signal corresponding to each plane wave emission angle within the selected time window; S8, constructing a matrix equation group between the blood flow velocity in a rectangular coordinate system, the emission angle of the plane wave, and the Doppler axial velocity corresponding to each voxel of the blood flow at each emission angle of the plane wave of the ultrasound; S9. Obtain the blood flow vector velocity by solving the matrix equation group.

5. The method according to claim 4, characterized in that The step B further comprises the following sub-steps: S11, generating a transient image of the blood flow vector velocity field at the current time on a display device according to the blood flow vector velocity; and / or, S12. Displaying a dynamic change image of the blood flow vector velocity field by sliding a time window according to the blood flow vector velocity.

6. The method according to claim 4, characterized in that The step B further comprises the following sub-steps: S10, performing interpolation and smoothing operations on the blood flow vector velocity.

7. The method according to claim 2, characterized in that: In step S1, the transmission delay between channels of the ultrasonic phased array is controlled to transmit plane waves at different angles.

8. The method according to claim 2, characterized in that: In the step S1, the type of ultrasonic wave emitted is a non-focused wave or a focused acoustic wave emitted in a synthetic aperture manner.

9. The method according to claim 2, characterized in that: In the step S1, Hadamard coding refers to N-order Hadamard coding, where N is an integer between 2 and 256, and N, N / 12 or N / 20 must be an integer power of 2, and the pulses are encoded into positive pulses and negative pulses according to the values ​​of the Hadamard matrix.

10. The method according to claim 2, characterized in that In the step S3, the collected N groups of continuous echo signals are linearly superimposed according to the value of each row in the given Hadamard matrix to achieve echo signal decoding.

11. The method according to claim 2, characterized in that In step S3, the delay applied in step S1 is subtracted from the N consecutive decoded echo signals to achieve delay compensation.

12. The method according to claim 2, characterized in that: In the step S4, the steps are repeated with a composite transmission frequency CPRF, wherein the Doppler velocity measurement range (-v max to v max ): Where c is the speed of sound in the tissue and f0 is the center frequency of ultrasound.

13. The method according to claim 3, characterized in that In the step S5, the beamforming method is any one of the following: a delay-addition algorithm, a frequency-domain-beam-domain migration algorithm, an adaptive beamforming algorithm, and a spatial compounding method.

14. The method according to claim 3, characterized in that In the step S5, the method of filtering out clutter is high-pass filtering or singular value decomposition.

15. The method according to claim 4, characterized in that In the step S7, the Doppler frequency estimation method is a delayed autocorrelation method.

16. The method according to claim 4, characterized in that In the steps S8-S9, when a one-dimensional probe is used to estimate the blood flow vector velocity in a two-dimensional plane, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each ultrasonic transmitting and receiving pair (the pth transmitting angle The qth receiving angle )have Φ IR (p,q,x,z,t)=arg[IQ(p,q,x,z,t)*IQ * (p,q,x,z,t-t PRF )] (2) Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t PRF Indicates the transmission interval corresponding to the pulse repetition frequency PRF; According to the geometric relationship, construct an NM×2 matrix K IR , Among them, the subscripts x and z represent the components of the angle vector in the lateral direction and depth direction, N and M represent the number of transmitting and receiving angles, respectively, and the blood flow velocity vector is solved Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , represents K IR The pseudo-inverse matrix, v x and v z They are the projections of blood flow velocity in the lateral direction and depth direction, respectively.

17. The method according to claim 4, characterized in that In the steps S8-S9, when the two-dimensional probe is used to estimate the blood flow vector velocity in three-dimensional space, a phase shift matrix Φ is constructed based on the autocorrelation of the signal. IR , for each ultrasonic transmitting and receiving pair (the pth transmitting angle The qth receiving angle )have Φ IR (p,q,x,y,z,t)=arg[IQ(p,q,x,y,z,t)*IQ * (p,q,x,y,z,t-t PRF )] (5) Among them, IQ represents the image data after clutter filtering, x represents the horizontal direction, z represents the depth direction, and t PRF Indicates the transmission interval corresponding to the pulse repetition frequency PRF; According to the geometric relationship, construct a NM×3 matrix K IR , Among them, the subscripts x and z represent the components of the angle vector in the lateral direction and depth direction, N and M represent the number of transmitting and receiving angles, respectively, and the blood flow velocity vector is solved Among them, p inv (K IR )=(K T IR K IR ) -1 K T IR , represents K IR The pseudo-inverse matrix, V x ,V y and V z They are the projections of blood flow velocity on the x, y and z axes of the three-dimensional coordinate system respectively.

18. The method according to claim 6, characterized in that In the step S10, the interpolation method is any one of the following: nearest neighbor method, bilinear interpolation method, and multiple regression method.

19. The method according to claim 6, characterized in that In the step S10, the smoothing operation is mean filtering or Gaussian filtering.

20. The method according to claim 1, characterized in that The method is used for any of the following blood flow imaging: blood flow in small blood vessels in the brain, spinal cord, kidney, liver, tumor, carotid artery, jugular vein, and intracardiac cavity of humans or animals.

21. A Doppler imaging system based on multi-angle plane wave Hadamard coding, characterized in that: include: A multi-angle ultrasonic echo signal and instantaneous blood flow image signal acquisition module is used to transmit N groups of ultrasonic waves phase-encoded using Hadamard coding into a blood flow imaging area, wherein each group of ultrasonic waves includes N continuous plane waves with different angles and separated by a predetermined time delay, collect N groups of ultrasonic echo signals corresponding to the N groups of ultrasonic waves and decode them according to the Hadamard matrix to obtain ultrasonic echo signals corresponding to the emission angles of the N plane waves, and repeatedly perform this step at a predetermined frequency to obtain continuous multi-angle ultrasonic echo signals; and, based on the continuous multi-angle ultrasonic echo signals, obtain an instantaneous blood flow image signal corresponding to the time window; The blood flow vector velocity field transient image and / or blood flow vector velocity field dynamically changing image generation module is used to construct and solve a matrix equation group using the results obtained by Doppler frequency estimation of the blood flow image signal, as well as the blood flow velocity and the emission angle of the plane wave to obtain the blood flow vectorization velocity, and generate a blood flow vector velocity field transient image and / or display a blood flow vector velocity field dynamically changing image based on the blood flow vectorization velocity.

22. A Doppler imaging system based on multi-angle plane wave Hadamard coding, characterized in that: The system is used to perform the method according to claim 1, wherein the system comprises: An ultrasonic transducer, used for transmitting ultrasonic signals to the entire blood flow measurement area and receiving ultrasonic echo signals; Multi-channel ultrasonic transmitting and receiving system, used to generate a specific pulse sequence to excite the ultrasonic transducer to transmit ultrasonic waves, sample and store ultrasonic echo signals; A user operating system, used for the user to configure ultrasound emission and acquisition parameters and adjust signal processing parameters and steps; Signal processing module, including pulse encoding and decoding module, image reconstruction module, orthogonal demodulation module, clutter filtering module, autocorrelation module, and velocity vector solution module; The image display device is used to display a user operation interface, a transient image of a blood flow vector velocity field, and / or a dynamic change image of a blood flow vector velocity field.

23. A Doppler imaging system based on multi-angle plane wave Hadamard coding, characterized in that: include: A memory for storing computer executable instructions; as well as, A processor, configured to implement the steps in the method according to any one of claims 1 to 16 when executing the computer executable instructions.

24. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, and when the computer-executable instructions are executed by a processor, the steps in the method according to any one of claims 1 to 16 are implemented.

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