CN112754529A - Ultrasonic plane wave imaging method and system based on frequency domain migration and storage medium - Google Patents
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Abstract
The invention provides an ultrasonic plane wave imaging method, device and storage medium based on frequency domain migration, comprising the following steps: obtaining echo signals received under three emission angles; constructing echo signal frequency domain space coordinates corresponding to the image frequency domain space coordinates; performing Fast Fourier Transform (FFT) on echo signals under each emission angle along the space direction, and performing non-uniform Fourier transform (NUDFT) on the obtained frequency spectrum signals along the time direction to obtain coordinates of the echo signals in the frequency domain space of the echo signals; the calculation of the non-uniform Fourier transform is completed based on a low-rank matrix constructed by utilizing a Chebyshev polynomial; and performing Inverse Fast Fourier Transform (IFFT) on the filtered signals, compounding echo signals under the three emission angles, and performing inverse fast Fourier transform to obtain a compounded ultrasonic image. The invention greatly improves the speed of ultrasonic plane wave imaging, can obtain high-quality images and can also ensure higher imaging frame frequency.
Description
Technical Field
The invention relates to the technical field of medical imaging, in particular to an ultrasonic plane wave imaging method and system based on frequency domain migration and a storage medium.
Background
Ultrasonic imaging has the advantages of non-invasion, safety, convenience, high real-time performance and the like, is widely applied to fetal, cardiac and abdominal imaging, and is one of the most important image modes in clinical diagnosis.
The traditional ultrasonic imaging adopts a focused wave line-by-line scanning imaging mode, namely, a column of an image is obtained by transmitting focused waves and receiving echo signals once, so that an image can be formed by hundreds of transmitting-receiving processes, the imaging speed is generally 20-100 frames/second, and the frame frequency of the traditional ultrasonic imaging is limited. In recent years, researchers put forward a plane wave imaging mode, and can obtain an ultrasonic image by transmitting plane waves once, so that the frame frequency of the image is greatly improved to 4000-15000 frames/second, the phenomenon that the existing traditional ultrasonic imaging cannot detect can be detected, and a road is paved for a series of new clinical applications, such as ultrafast Doppler imaging, shear wave elastography, brain function imaging and the like.
In order to improve the imaging quality of the ultrasonic plane wave, a method of spatially compounding ultrasonic images obtained from a plurality of emission angles is widely used. This method, while improving image quality, greatly reduces the imaging frame rate. Meanwhile, the ultrasonic plane wave imaging needs to perform point-by-point delay overlay (DAS) calculation, and in addition, ultrasonic images at multiple angles (generally 11 to 75 angles) need to be processed in real time, so that the calculation amount is huge, and a huge challenge is provided for the data processing performance.
Frequency domain beamforming can greatly reduce computational complexity thanks to a Fast Fourier Transform (FFT) algorithm. However, in the current frequency domain ultrasonic imaging, linear frequency interpolation is mostly adopted, and errors are generated, so that the image quality is reduced. In addition, the non-uniform fourier transform (NUDFT) based on min-max interpolation is widely applied to the field of magnetic resonance imaging, but when ultrasonic plane wave imaging is performed, interpolation functions under different deflection angles need to be calculated in real time, and the real-time requirement cannot be met. Therefore, how to perform the ultrasonic plane wave frequency domain imaging rapidly and with high quality and compound the images with less angles so as to obtain the ultrasonic plane wave image with high quality and high frame frequency has important significance.
Disclosure of Invention
The invention aims to provide an ultrasonic plane wave imaging method, device and storage medium based on frequency domain migration. Since only three-angle plane waves need to be transmitted, a higher imaging frame rate can also be ensured.
Therefore, the invention provides the following technical scheme:
in one aspect, the present invention provides a method for ultrasonic plane wave imaging based on frequency domain migration, where the method includes:
step 1, obtaining echo signals received under three emission angles by adjusting the angles of the emission plane waves;
and 4, aiming at the echo signals Si (t, x) under each emission angle after delay processing, wherein t represents time and x represents space, carrying out fast Fourier transform along the x direction to obtain frequency spectrum signalsLocation of its spatial spectrumDetermined by frequency domain migration; to pairCarrying out non-uniform Fourier transform along the t direction to obtain the echo signalCorresponding signalThe position k of its time spectrumimgDetermined by frequency domain migration; wherein i represents an emission angle, and i is 1, 2 or 3; the calculation of the non-uniform Fourier transform is completed based on a low-rank matrix constructed by utilizing a Chebyshev polynomial;
Step 7, under three emission anglesIs compounded and then is followedAnd performing inverse fast Fourier transform on the direction to obtain a composite ultrasonic image S (Z, X).
Further, the delay processing is performed on the echo signals of each emission angle, and the processing includes: and carrying out frequency domain delay processing on the echo signals of all the emission angles.
Further, the frequency domain delay processing includes: performing one-dimensional Fourier transform on the signal of each channel according to a delay parameter delta t ═ xsin (theta)/C0,C0Multiplying the Fourier transformed signal by e for sound velocity, theta for emission angle and x for x coordinate of each array element position of the ultrasonic probe-j2πfΔtAnd f is the frequency of the signal along the depth direction, and then inverse Fourier transform is carried out to obtain a delayed echo signal.
Further, the calculation of the non-uniform fourier transform is performed based on a low-rank matrix constructed using chebyshev polynomials, and includes:
constructing a low-rank matrix by using a K-order Chebyshev polynomial;
a matrix obtained by dividing the uniform Fourier transform matrix and the discrete Fourier transform matrix element by element is approximate to the low-rank matrix;
completing the computation of the non-uniform Fourier transform based on the low-rank matrix and discrete Fourier transform matrix.
Further, to the signalEdge kimgAnd (3) performing filtering processing on the direction, wherein the filtering processing comprises the following steps:
for the signalAnd the frequency response of the filter performs multiplication operation to realize filtering processing.
constructing a sliding window with a group of three angles, and obtaining frequency domain images under three emission angles of each groupAnd (6) compounding.
Further, still include:
and performing envelope taking and logarithmic compression on the compounded ultrasonic image to obtain a Bmode image.
Further, the formula for the frequency domain migration is:
wherein, KzAnd KxIs the spatial frequency of the image and is, b=0,...,Nz-1, wherein L is the probe aperture, NzAnd NxThe axial and lateral dimensions of the image, Z, respectivelymaxIs the maximum imaging depth.
In yet another aspect, the present invention further provides an ultrasonic plane wave imaging apparatus based on frequency domain migration, the apparatus comprising:
the acquisition unit is used for acquiring echo signals received under three emission angles by adjusting the angles of the emission plane waves;
the time delay processing unit is used for carrying out time delay processing on the echo signals of all the emission angles obtained by the acquisition unit;
a frequency domain space construction unit for constructing image space coordinates (Z, X) and calculating the mapImage space frequency, carrying out frequency domain migration according to the image space frequency, and calculating echo signal frequency domain space coordinates corresponding to the image frequency domain space coordinatesWherein Z represents an image axial coordinate and X represents an image lateral coordinate; k is a radical ofimgRepresents the axial frequency domain wavenumber position of the echo signal,representing the spatial wave number position of the echo signal along the lateral direction;
a frequency domain migration unit, configured to perform fast fourier transform in the x direction on echo signals Si (t, x) at each emission angle after being delayed by the delay processing unit, where t represents time and x represents space, to obtain a frequency spectrum signalLocation of its spatial spectrumDetermined by the frequency domain space construction unit; to pairCarrying out non-uniform Fourier transform along the t direction to obtain the echo signalCorresponding signalIts time spectrum position kimgDetermined by the frequency domain space construction unit; wherein i represents an emission angle, and i is 1, 2 or 3; the calculation of the non-uniform Fourier transform is completed based on a low-rank matrix constructed by utilizing a Chebyshev polynomial;
a filtering unit for obtaining the frequency domain migration unitEdge kimgFiltering the direction to obtain a filtered signal
A combining unit for combining the signals obtained by the filtering unitEdge kimgPerforming inverse fast Fourier transform on the direction to obtain a frequency domain imageFor three emission anglesIs compounded and then is followedAnd performing inverse fast Fourier transform on the direction to obtain a composite ultrasonic image S (Z, X).
In still another aspect, the present invention further provides a computer-readable storage medium, which stores a computer program, wherein the computer program is executed to perform any one of the above-mentioned methods for ultrasonic plane wave imaging based on frequency domain migration.
The invention has the advantages and positive effects that: the invention provides a three-angle ultrasonic plane wave compound imaging method based on frequency domain migration, which is characterized in that a low-rank matrix is constructed by utilizing a Chebyshev polynomial to approximate an accurate matrix, NUDFT calculation is converted into few FFT calculation, the ultrasonic plane wave imaging speed is greatly improved, and echo signals under positive, negative and zero angles are subjected to frequency domain compounding, so that a high-quality image is obtained. In addition, the method only needs three-angle plane waves for compound imaging, so that a higher imaging frame frequency can be ensured.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a flow chart of an ultrasonic plane wave imaging method based on frequency domain migration according to the present invention;
FIG. 2 is a schematic diagram of different deflection angles of ultrasonic plane waves according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of three-angle compound imaging by emitting a sequence of different deflection angles according to an embodiment of the present invention;
fig. 4 is a comparison result of contrast and image resolution of images obtained by the DAS-based composite imaging method according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In order to improve the imaging quality of the ultrasonic plane waves and keep higher precision, the invention provides the ultrasonic plane wave imaging method based on frequency domain migration. Since only three-angle plane waves need to be transmitted, a higher imaging frame rate can also be ensured.
As shown in fig. 1, it shows a flowchart of an ultrasonic plane wave imaging method based on frequency domain migration according to an embodiment of the present invention, the method includes the following steps:
step 1: echo signals received under three transmitting angles are obtained by adjusting the angle of transmitting the plane wave.
Specifically, the emission angles include three, θ, according to the ultrasonic plane wave deflection angle shown in fig. 2-0 DEG and theta+Wherein 0 DEG < | theta-|,θ+Is less than or equal to 5 degrees. Respectively receiving echo signals Si corresponding to the three emission angles, wherein i represents the emission angle, and 1, 2 or 3 is selected as i; its dimension is Nt×NeWherein N istFor echo signals at different points in time, NeIs an array element of the ultrasonic probe.
Step 2: and preprocessing the echo signals of all the transmitting angles.
The pretreatment comprises the following steps: firstly, determining the number of time and space Fourier transform points, ntFFT and nxFFT, respectively corresponding to the number of points of echo signal Si (t, x) after Fourier transform along time t and space x, and according to sampling frequency fsAnd array element spacing p, determining frequency domain wave number pointWhere l is a calculation index, l is 00Is acoustic velocity, airspace wavenumber pointWherein, m is a calculation index,and according to k and kxAnd constructing two-dimensional frequency domain grid points.
And secondly, for the echo signal with the transmitting angle theta not equal to 0, carrying out delay processing on the data acquired by each array element according to the transmitting delay. In order to ensure the accuracy, a frequency domain delay method may be adopted, that is, a signal of each channel is subjected to one-dimensional fourier transform, and according to a delay parameter Δ t ═ xsin (θ)/C0,C0Multiplying the Fourier transformed signal by e for sound velocity, theta for emission angle and x for x coordinate of each array element position of the ultrasonic probe-j2πfΔtAnd f is the frequency of the signal along the depth direction, and then inverse Fourier transform is carried out to obtain a delayed signal.
And step 3: and constructing an image space coordinate, calculating an image space frequency, carrying out frequency domain migration according to the image space frequency, and calculating an echo signal frequency domain space coordinate corresponding to the image frequency domain space coordinate.
In particular, image space coordinates (Z, X) are constructed, where Z represents the image axial coordinates, X represents the image lateral coordinates,b denotes a calculation index, b ═ 0z-1;d denotes the calculation of the index,Nzand NxThe axial and lateral dimensions of the image, Z, respectivelymaxIs the maximum imaging depth. Then, the spatial frequency of the image is calculated, wherein L is the aperture of the probe,then, according to the frequency domain migration formulaThe image frequency domain space coordinate (K) can be calculatedz,Kx) Corresponding echo signal frequency domain space coordinatekimgRepresents the axial frequency domain wavenumber position of the echo signal,representing the spatial wavenumber position of the echo signal in the lateral direction.
And 4, step 4: performing fast Fourier transform on echo signals under each emission angle after delay processing along the spatial direction to obtain frequency spectrum signals; and carrying out non-uniform Fourier transform on the frequency spectrum signal along the time direction to obtain a signal corresponding to the echo signal in the echo signal frequency domain space coordinate, wherein the calculation of the non-uniform Fourier transform is completed on the basis of a low-rank matrix constructed by utilizing a Chebyshev polynomial.
Specifically, one-dimensional Fourier transform is carried out on the collected echo signals Si (t, x) along the x direction, t represents time, x represents space, i represents a transmitting angle, and i is 1, 2 or 3; obtaining a spectral signalLocation of its spatial spectrumDetermined by frequency domain migration. Next, a calculation is requiredOf the signal (c). Due to KxAnd kxAre all uniformly sampled along the x-direction and can be quickly adjusted to the same size by Fast Fourier Transform (FFT). Whereas for signals in the direction of t, due to kimgAre non-uniformly distributed, and therefore need to be onPerforming non-uniform Fourier transform (NUDFT) to obtain the echo signalCorresponding signalIts time spectrum position kimgDetermined by frequency domain migration. If selected, theOnly one-dimensional non-uniform fourier transform along the direction t needs to be performed.
Preferably, for the one-dimensional non-uniform fourier transform mentioned in step 4, the specific method is: the Discrete Fourier Transform (DFT) can realize the NUDFT, but has high computational complexity and long computation time, and cannot be practically applied. The matrix obtained by dividing the NUDFT matrix and the DFT matrix one by one element can be approximated by a low-rank matrix with the rank of K (K < ntFFT), and the approximation precision is high. Thus, the computation of the NUDFT can be reduced to the summation of K weighted DFTs, which can be accelerated by the FFT, thereby greatly reducing the computation time. In order to ensure the stability of the low-rank approximate calculation, Chebyshev polynomial expansion is adopted. By an n-order Chebyshev polynomial Tn(x)=cos(ncos-1(x)),x∈[-1,1]Set of constructs (T)0,T1,...,TnIs a set of orthogonal bases with a rank of at most n. Thus, a low-rank matrix A is constructed using a Chebyshev polynomial of order KKThe calculation of NUDFT can be expressed asWherein Fjk=e-2πijk/NS (t) is a time signal for the basis of the FFT calculation,the multiplication of the expression elements is performed, N represents the number of points calculated by FFT, and the value range of the rank K of the low-rank matrix is more than or equal to 7 and less than or equal to 10.
And 5: and 4, filtering the signal obtained in the step 4 to obtain a filtered signal.
For that obtained in step 4Can be along kimgAnd filtering is carried out in the direction, only signals in the interested frequency range are reserved, low-frequency and high-frequency noises are removed, and the image quality is improved. In particular, the amount of the solvent to be used,where H (f) is the frequency response of the filter. Since the original signal is already in the frequency domain, the filtering process can be directly realized by the multiplication operation. H (f) may be a low pass, band pass or high pass filter.
Step 6: and 5, performing inverse fast Fourier transform on the filtered signal obtained in the step 5 to obtain a frequency spectrum image.
For the three angles of the filtered signal Si obtained in step 5filter(kimg,kx) Respectively along kimgPerforming IFFT to obtain a frequency spectrum image
And 7: and (4) compounding the frequency spectrum images under the three emission angles obtained in the step (6), and then performing inverse fast Fourier transform to obtain a compounded ultrasonic image.
In particular, the signals of the three angles are combined, i.e.Then alongIn the direction, inverse fourier transform is performed by IFFT to obtain a composite ultrasound image S (Z, X).
And 8: and (4) respectively carrying out Hilbert transform on the ultrasonic images obtained in the step (7) to obtain signal envelopes, carrying out logarithmic compression, and finally obtaining Bmode images.
In practical imaging, sequences of different deflection angles can be transmitted, such as: negative, zero, positive … …, in the imaging process, can form a sliding window of three angle data groups, namely negative zero positive, negative, positive negative zero, … …, each group carries out three-angle compound imaging once, thereby realizing high-quality and high-frame frequency ultrasonic plane wave imaging.
According to the three-angle ultrasonic plane wave compound imaging method based on frequency domain migration, a low-rank matrix is constructed by utilizing the Chebyshev polynomial to approximate an accurate matrix, NUDFT calculation is converted into few FFT calculation, the ultrasonic plane wave imaging speed is greatly improved, and echo signals under positive, negative and zero angles are subjected to frequency domain compounding, so that a high-quality image is obtained. In addition, the method only needs three-angle plane waves for compound imaging, so that a higher imaging frame frequency can be ensured.
For the convenience of understanding, the method for ultrasonic plane wave imaging based on frequency domain migration in the present invention is described below as a specific example. The method comprises the following steps:
step 1: three emission angles are theta-=-0.43°,0°,θ+The echo signals Si (i is 1, 2, or 3) corresponding to the three transmission angles are acquired at 0.43 °, and the dimension N ist×Ne,Nt1352 is the number of echo signal points, Ne128 is the array element number of the ultrasonic probe.
Step 2: determining the number of ntFFT 1352 and nxFFT 256 of the time Fourier transform, and the sampling frequency fs20.8HMz, 0.3mm of array element spacing p, sound velocity C0Calculating frequency domain wave number points as 1540m/s1, ntFFT-1, spatial domain wavenumber pointAnd according to k and kxAnd constructing two-dimensional frequency domain grid points. Next, for the echo signal Si (i ═ 1 or 3) with the transmission angle θ ≠ 0, the signal of each channel is subjected to one-dimensional fourier transform, and xsin (θ)/C is obtained according to the delay parameter Δ t ═ xsin (θ)/C0,C0Multiplying the Fourier transformed signal by e for sound velocity, theta for emission angle and x for x coordinate of each array element position of the ultrasonic probe-j2πfΔtAnd f is the frequency of the signal along the depth direction, and then inverse Fourier transform is carried out to obtain a delayed signal.
And step 3: image space coordinates (Z, X) are constructed, wherein,b=0,...,Nz-1,Nzand NxThe axial and lateral dimensions of the image, Z, respectivelymaxIs the maximum imaging depth; n is a radical ofz=1352,Nx=128,Zmax50mm, and 38.4 mm. Then, the spatial frequency of the image is calculated,b=0,...,Nz-1, wherein L is the probe aperture. Then, according to the frequency domain migration formulaThe image frequency domain space coordinate (K) can be calculatedz,Kx) Corresponding echo signal frequency domain space coordinate
And 4, step 4: advancing the collected echo signal Si (t, x) along the x directionPerforming one-dimensional FFT to obtain a frequency spectrum signalTo pairNUDFT is carried out to obtain corresponding valueNamely, it isConstructing a low-rank matrix A by using 7-order Chebyshev polynomials7The calculation of NUDFT can be expressed asWherein Fjk=e-2πijk/NAre the basis of the FFT calculation.
And 5: to pairEdge kimgAnd (3) filtering in the direction: filtered signalWherein H (f) is the frequency response of the band-pass filter, and the pass band range is (0.2-0.8) fnqWhereinAt the nyquist frequency.
Step 6: for Si at three anglesfilter(kimg,kx) Respectively along kimgIFFT is carried out in the direction to obtain a frequency domain image
And 7: echo signals of three angles are compounded:then alongThe directions are subjected to IFFT transformation to obtain a composite ultrasonic image S (Z, X).
And 8: and (4) respectively enveloping and carrying out logarithmic compression on the S (Z, X), and finally obtaining a Bmode image.
And step 9: three sliding windows with one group of angles, namely negative zero positive, zero positive and negative, positive negative zero and … … are constructed, as shown in fig. 3, each group performs one-time triangular compound imaging, and high-quality and high-frame-frequency ultrasonic plane wave imaging is realized.
Fig. 4 is a comparison of the results of ultrasonic plane wave imaging obtained by the method of the present embodiment with conventional DAS complex imaging, where fig. 4(a) is the results of conventional DAS complex imaging and fig. 4(b) is the results of complex imaging obtained by the method of the present embodiment. To quantify the results, the box labeled target points in FIG. 4(c) are used to compare the resolution of the images and the circle labeled regions are used to compare the contrast of the images. The quantification result shows that the average axial resolution of the traditional DAS image is 0.41mm, the average lateral resolution is 0.80mm, the CNR is 11.28dB, and the calculation time is 5.6 s; the average axial resolution of the image obtained by the method of the embodiment is 0.40mm, the average lateral resolution is 0.57mm, the CNR is 14.17dB, and the calculation time is 0.75 s. The lateral resolution, the CNR and the calculation time are all improved obviously.
The invention also provides an ultrasonic plane wave imaging device based on frequency domain migration, which corresponds to the ultrasonic plane wave imaging method based on frequency domain migration in the invention, and the device comprises:
the acquisition unit is used for acquiring echo signals received under three emission angles by adjusting the angles of the emission plane waves;
the time delay processing unit is used for carrying out time delay processing on the echo signals of all the emission angles obtained by the acquisition unit;
a frequency domain space construction unit for constructing image space coordinates (Z, X), calculating image space frequency, and performing the operation according to the image space frequencyFrequency domain migration, calculating echo signal frequency domain space coordinate corresponding to image frequency domain space coordinateWherein Z represents an image axial coordinate and X represents an image lateral coordinate; k is a radical ofimgRepresents the axial frequency domain wavenumber position of the echo signal,representing the spatial wave number position of the echo signal along the lateral direction;
a frequency domain migration unit, configured to perform fast fourier transform in the x direction on echo signals Si (t, x) at each emission angle after being delayed by the delay processing unit, where t represents time and x represents space, to obtain a frequency spectrum signalLocation of its spatial spectrumDetermined by the frequency domain space construction unit; to pairCarrying out non-uniform Fourier transform along the t direction to obtain the echo signalCorresponding signalIts time spectrum position kimgDetermined by the frequency domain space construction unit; wherein i represents an emission angle, and i is 1, 2 or 3; the calculation of the non-uniform Fourier transform is completed based on a low-rank matrix constructed by utilizing a Chebyshev polynomial;
a filtering unit for obtaining the frequency domain migration unitEdge kimgFiltering the direction to obtain a filtered signal
A combining unit for combining the signals obtained by the filtering unitEdge kimgPerforming inverse fast Fourier transform on the direction to obtain a frequency domain imageFor three emission anglesIs compounded and then is followedAnd performing inverse fast Fourier transform on the direction to obtain a composite ultrasonic image S (Z, X).
Further, the delay processing unit is specifically configured to perform frequency domain delay processing on the echo signal at each emission angle.
Further, the delay processing unit is specifically configured to perform one-dimensional fourier transform on the signal of each channel, and obtain the delay parameter Δ t — xsin (θ)/C0,C0Multiplying the Fourier transformed signal by e for sound velocity, theta for emission angle and x for x coordinate of each array element position of the ultrasonic probe-j2πfΔtAnd f is the frequency of the signal along the depth direction, and then inverse Fourier transform is carried out to obtain a delayed echo signal.
Further, the calculation of the non-uniform fourier transform is performed based on a low-rank matrix constructed using chebyshev polynomials, and includes:
constructing a low-rank matrix by using a K-order Chebyshev polynomial;
a matrix obtained by dividing the uniform Fourier transform matrix and the discrete Fourier transform matrix element by element is approximate to the low-rank matrix;
completing the computation of the non-uniform Fourier transform based on the low-rank matrix and discrete Fourier transform matrix.
Further, the filtering unit is specifically configured to: to pairAnd the frequency response of the filter performs multiplication operation to realize filtering processing.
Further, the composite unit is specifically configured to: constructing a sliding window with a group of three angles, and obtaining frequency domain images under three emission angles of each groupAnd (6) compounding.
Further, the composite unit is also configured to: and performing envelope taking and logarithmic compression on the compounded ultrasonic image to obtain a Bmode image.
Further, carrying out frequency domain migration according to the image space frequency, and calculating the echo signal frequency domain space corresponding to the image frequency domain spaceThe method comprises the following steps:
according to the formulaComputing image frequency domain space (K)z,Kx) Corresponding echo signal frequency domain space
Wherein, KzAnd KxIs the spatial frequency of the image and is,b=0,...,Nz-1,wherein L is the probe aperture, NzAnd NxAre respectively provided withIs the axial and lateral dimension of the image, ZmaxIs the maximum imaging depth.
The ultrasonic plane wave imaging device based on frequency domain migration according to the embodiment of the present invention is relatively simple in description since it corresponds to the ultrasonic plane wave imaging method based on frequency domain migration according to the above embodiment, and for the relevant similarities, please refer to the description in the above embodiment, and details are not described here.
The embodiment of the invention also discloses a computer-readable storage medium, wherein a computer instruction set is stored in the computer-readable storage medium, and when being executed by a processor, the computer instruction set realizes the ultrasonic plane wave imaging method based on frequency domain migration, which is provided by any one of the above embodiments.
In the embodiments provided in the present invention, it should be understood that the disclosed technical contents can be implemented in other manners. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. An ultrasonic plane wave imaging method based on frequency domain migration is characterized by comprising the following steps:
step 1, obtaining echo signals received under three emission angles by adjusting the angles of the emission plane waves;
step 2, carrying out time delay processing on the echo signals of all the emission angles;
step 3, constructing image space coordinates (Z, X), calculating image space frequency, carrying out frequency domain migration according to the image space frequency, and calculating echo signal frequency domain corresponding to the image frequency domain space coordinatesSpatial coordinatesWherein Z represents an image axial coordinate and X represents an image lateral coordinate; k is a radical ofimgRepresenting the frequency domain wavenumber position of the echo signal in the axial direction,representing the spatial wave number position of the echo signal along the lateral direction;
and 4, aiming at the echo signals Si (t, x) under each emission angle after delay processing, wherein t represents time and x represents space, carrying out fast Fourier transform along the x direction to obtain frequency spectrum signalsLocation of its spatial spectrumDetermined by frequency domain migration; to pairCarrying out non-uniform Fourier transform along the t direction to obtain the echo signalCorresponding signalThe position k of its time spectrumimgDetermined by frequency domain migration; wherein i represents an emission angle, and i is 1, 2 or 3; the calculation of the non-uniform Fourier transform is completed based on a low-rank matrix constructed by utilizing a Chebyshev polynomial;
Step 6, pairEdge kimgPerforming inverse fast Fourier transform on the direction to obtain a frequency spectrum image
2. The ultrasonic plane wave imaging method based on frequency domain migration according to claim 1, wherein the delay processing of the echo signals of each emission angle comprises: and carrying out frequency domain delay processing on the echo signals of all the emission angles.
3. The method of claim 2, wherein the frequency domain delay processing comprises: performing one-dimensional Fourier transform on the signal of each channel according to a delay parameter delta t ═ xsin (theta)/C0,C0Multiplying the Fourier transformed signal by e for sound velocity, theta for emission angle and x for x coordinate of each array element position of the ultrasonic probe-j2πfΔtAnd f is the frequency of the signal along the depth direction, and then inverse Fourier transform is carried out to obtain a delayed echo signal.
4. The method of claim 1, wherein the computation of the non-uniform fourier transform is performed based on a low rank matrix constructed using chebyshev polynomials and comprises:
constructing a low-rank matrix by using a K-order Chebyshev polynomial;
a matrix obtained by dividing the uniform Fourier transform matrix and the discrete Fourier transform matrix element by element is approximate to the low-rank matrix;
completing the computation of the non-uniform Fourier transform based on the low-rank matrix and discrete Fourier transform matrix.
5. The method of claim 1, wherein the signal is imaged based on frequency domain shifting ultrasonic plane wavesEdge kimgAnd (3) performing filtering processing on the direction, wherein the filtering processing comprises the following steps:
7. The method for ultrasonic plane wave imaging based on frequency domain migration according to claim 1, further comprising:
and performing envelope taking and logarithmic compression on the compounded ultrasonic image to obtain a Bmode image.
8. The ultrasonic plane wave imaging method based on frequency domain migration according to claim 1, wherein the formula of the frequency domain migration is as follows:
9. An ultrasonic plane wave imaging device based on frequency domain migration, the device comprising:
the acquisition unit is used for acquiring echo signals received under three emission angles by adjusting the angles of the emission plane waves;
the time delay processing unit is used for carrying out time delay processing on the echo signals of all the emission angles obtained by the acquisition unit;
a frequency domain space construction unit for constructing image space coordinates (Z, X), calculating image space frequency, performing frequency domain migration according to the image space frequency, and calculating echo signal frequency domain space coordinates corresponding to the image frequency domain space coordinatesWherein Z represents an image axial coordinate and X represents an image lateral coordinate; k is a radical ofimgRepresenting the axial frequency of an echo signalThe position of the wave number in the domain,representing the spatial wave number position of the echo signal along the lateral direction;
a frequency domain migration unit, configured to perform fast fourier transform in the x direction on echo signals Si (t, x) at each emission angle after being delayed by the delay processing unit, where t represents time and x represents space, to obtain a frequency spectrum signalLocation of its spatial spectrumDetermined by the frequency domain space construction unit; to pairCarrying out non-uniform Fourier transform along the t direction to obtain the echo signalCorresponding signalThe position k of its time spectrumimgDetermined by the frequency domain space construction unit; wherein i represents an emission angle, and i is 1, 2 or 3; the calculation of the non-uniform Fourier transform is completed based on a low-rank matrix constructed by utilizing a Chebyshev polynomial;
a filtering unit for obtaining the frequency domain migration unitEdge kimgFiltering the direction to obtain a filtered signal
A combining unit for combining the signals obtained by the filtering unitEdge kimgPerforming inverse fast Fourier transform on the direction to obtain a frequency domain imageFor three emission anglesIs compounded and then is followedAnd performing inverse fast Fourier transform on the direction to obtain a composite ultrasonic image S (Z, X).
10. A computer-readable storage medium, in which a computer program is stored, wherein the computer program is executed to perform the method for ultrasonic plane wave imaging based on frequency domain migration according to any one of claims 1 to 8.
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