阅读说明：本技术 一种带有截断因子的高鲁棒性符号相干系数超声成像方法 (High-robustness symbol coherence coefficient ultrasonic imaging method with truncation factor ) 是由 王平 李锡涛 李倩文 何峰宇 梁家祺 何理 王慧悦 周瑜 陈靖翰 沈悦 武超 于 2021-08-18 设计创作，主要内容包括：本发明涉及一种带有截断因子的高鲁棒性符号相干系数超声成像方法,属于超声成像技术领域。该方法包括：S1：对超声阵元接收的回波信号进行预处理；S2：提取出各个单发全收模式下的回波数据的符号值；S3：在合成孔径模式下,依次得到符号相干系数表；S4：求取各个发射孔径下的符号相干系数表均值作为当前符号相干系数表的截断阈值；S5：利用该截断阈值对回波符号相干系数进行截断处理；S6：对回波构成的延时叠加波束形成器的输出进行加权,依次得到单发全收模式下的单帧成像子图；S7：对多张单发全收模式下的成像子图进行空间复合,得到最终成像结果；本发明能在几乎不损失符号相干系数分辨率性能的同时,大幅度提高背景成像质量,解决背景图像失真问题。(The invention relates to a high robustness symbol coherence coefficient ultrasonic imaging method with a truncation factor, and belongs to the technical field of ultrasonic imaging. The method comprises the following steps: s1: preprocessing echo signals received by the ultrasonic array elements; s2: extracting the symbol value of the echo data in each single-transmitting and full-receiving mode; s3: under the synthetic aperture mode, a symbol coherence coefficient table is obtained in sequence; s4: solving the mean value of the symbol coherent coefficient table under each transmitting aperture as the truncation threshold of the current symbol coherent coefficient table; s5: utilizing the truncation threshold to perform truncation processing on the echo symbol coherence coefficient; s6: weighting the output of a delay superposition beam former formed by echo waves to sequentially obtain a single-frame imaging subgraph in a single-transmission full-receiving mode; s7: carrying out spatial compounding on a plurality of imaging subgraphs in a single-shot full-receiving mode to obtain a final imaging result; the invention can greatly improve the background imaging quality and solve the problem of background image distortion while hardly losing the resolution performance of the symbol coherence coefficient.)

1. A high robustness symbol coherence coefficient ultrasonic imaging method with truncation factors is characterized in that: the method specifically comprises the following steps:

s1: preprocessing echo signals received by the ultrasonic array elements to obtain processed ultrasonic echo data, and storing the data obtained by each transceiving aperture into a data table A;

s2: extracting the symbol values of the echo data in each single-transmitting and full-receiving mode, and sequentially storing the symbol values in a data table B_signPerforming the following steps;

s3: under the synthetic aperture mode, calculating time domain symbol coherence coefficients corresponding to each transmitting array aperture under the single-transmitting and full-receiving mode according to the fluctuation characteristics of the ultrasonic echo symbol values, and sequentially obtaining a symbol coherence coefficient table;

s4: calculating the mean value of the symbol coherent coefficient table under each transmitting aperture as the truncation threshold SATC of the current symbol coherent coefficient table_sign；

S5: utilizing the truncation threshold to perform truncation processing on the echo symbol coherence coefficient, reserving the symbol coherence coefficient of the strong coherence part, and performing compensation optimization on the symbol coherence coefficient of the weak coherence part to obtain a truncated symbol coherence coefficient table TSCF;

s6: weighting the output of a delay superposition beam former formed by echo waves to sequentially obtain single-frame imaging subgraphs in a single-transmission and full-reception mode;

s7: and (3) carrying out spatial compounding on a plurality of imaging subgraphs in the single-shot full-receiving mode to obtain a final ultrasonic imaging result of the high-robustness symbol coherence coefficient beam former with the truncation factor.

2. The method of claim 1, wherein the method comprises the following steps: in S1, the processing the echo signals received by the ultrasound array element includes: amplifying, AD converting, noise filtering, and storing data obtained by each transceiving aperture into a number table A, wherein A is a three-dimensional number table with dimension of D multiplied by M multiplied by N, D represents the total sampling time number of echo waves, N represents the number of transmitting apertures, and M represents the number of receiving apertures; decomposing the detection area into Q multiplied by H pixel points, and sequentially calculating the focusing delay of each receiving and transmitting aperture to each detection point of the detection area as follows:

wherein f is_sRepresenting the sampling frequency, t_offThe time interval from the beginning of transmitting ultrasonic waves to the first time of receiving the echo is represented, c represents the propagation speed of the ultrasonic waves in a medium of a detection region, q represents the longitudinal serial number of a pixel point in the detection region, h represents the transverse serial number of the pixel point in the detection region, m represents a receiving aperture serial number, and n represents a transmitting aperture serial number; x (q, h), x (0, m), x (0, n), y (q, h), y (0, m), y (0, n) respectively represent the abscissa and ordinate of the point (q, h) (0, m) (0, n); Δ (q, h, m, n) represents the amount of delay required by the receive aperture m at the current sampling instant when the pixel point (q, h) is detected and the transmit aperture is n.

3. The method of claim 1, wherein the method comprises the following steps: in S2, the symbol values of the echo data in the single-transmission full-reception mode are extracted and stored in the count table B in sequence_signIn (1), namely:

wherein, A (delta, m, n) represents the delayed data obtained by the receiving aperture m when the target pixel point (q, h) is detected and the transmitting aperture is n; b is_sign(Δ, m, n) represents the number of delays obtained by the receiving aperture m when detecting the target pixel (q, h) and when the transmitting aperture is nAccording to the sign value.

4. The method of claim 1, wherein the method comprises the following steps: in S3, in the synthetic aperture mode, time domain symbol coherence coefficients corresponding to each transmit array aperture in the single-transmit full-receive mode are calculated according to the fluctuation characteristics of the ultrasonic echo symbol values, and a symbol coherence coefficient table is sequentially obtained:

SCF_nand (q, h) represents the echo symbol coherence coefficient corresponding to the pixel point (q, h) in the detection region under the nth transmitting aperture, and the number N of the transmitting apertures is equal to the number M of the receiving apertures.

5. The method of claim 1, wherein the method comprises the following steps: in the step S4, the mean value of the symbol coherence coefficient table at each transmit aperture is obtained as the truncation threshold SATC of the current symbol coherence coefficient table_sign：

Wherein, SATC_sign(n) a truncation threshold representing a table of symbol coherence coefficients at the nth transmit aperture; and Q multiplied by H represents the total number of pixel points in the detection rectangular area.

6. The method of claim 1, wherein the method comprises the following steps: in S5, the truncation threshold is used to perform truncation processing on the echo symbol coherence coefficient, retain the symbol coherence coefficient of the strong coherent part, and perform compensation optimization on the symbol coherence coefficient of the weak coherent part, so as to obtain a truncated symbol coherence coefficient table TSCF:

TSCF_n(q,h)＝max(SATC_sign(n)，SCF_n(q,h))

TSCF_n(q, h) denotes the sign coherence coefficient of the nth transmit aperture with a truncation factor at the pixel point (q, h), SCF_n(q, h) represents the original symbol coherence coefficient, SATC, of the nth transmit aperture at pixel point (q, h)_sign(n) represents a symbol coherence coefficient truncation threshold at the nth transmit aperture; max (·) represents the maximum value solving function.

7. The method of claim 1, wherein the method comprises the following steps: in S6, the outputs of the delay superposition beam former formed by the echoes are weighted, and single-frame imaging subgraphs in the single-transmit and full-receive mode are sequentially obtained:

whereinRepresenting the output gray value of a pixel point (q, h) in a detection area of a beam former based on a symbol coherence coefficient TSCF with a truncation factor under the nth transmitting aperture, and G (q, h) representing the output gray value of a pixel point (q, h) in the detection area of an original beam former DAS; TSCF_nAnd (q, h) represents the symbol coherence coefficient of the nth transmitting aperture with the truncation factor on the pixel point (q, h).

8. The method of claim 1, wherein the method comprises the following steps: in S7, spatially compounding the imaging subgraphs in the single-shot full-receiving mode to obtain a final ultrasound imaging result:

wherein, GZ_TSCF(q, h) represents the final output gray value of the pixel point (q, h) based on the beam former of the symbol coherence coefficient TSCF with the truncation factor in the synthetic aperture mode;and (3) under the nth transmitting aperture, the output gray value of a pixel point (q, h) in the detection region based on a beam former of a symbol coherence coefficient TSCF with a truncation factor is represented.

Technical Field

The invention belongs to the technical field of ultrasonic imaging, and relates to a high-robustness symbol coherence coefficient ultrasonic imaging method with a truncation factor.

Background

The most widely used And simplest beam forming technique in ultrasound imaging is Delay And Sum (DAS), which calculates the Delay of the received echo signal according to the geometric position of the array element channels, And then aligns And adds the delayed data. The traditional DAS algorithm is low in complexity and high in imaging speed, but the main lobe width is increased due to the fact that the traditional DAS algorithm adopts fixed window function weighting, and the resolution is low.

In recent years, adaptive algorithms have been increasingly studied in order to improve the contrast and resolution of beamforming algorithms. Among them, the Coherence Factor (CF) algorithm has been widely studied due to its advantages of high resolution and high contrast. It can be used to measure the focus quality of an ultrasonic beam and to substantially suppress the formation of side lobe artifacts. Sign Coherence Factor (SCF) is a typical type of Coherence Factor algorithm, and has received attention because it only uses Sign values to calculate, and thus has great advantages in algorithm complexity. However, since it is similar to the conventional coherence coefficient algorithm, it can suppress the incoherent signal too severely, thereby causing image distortion problem and large area black region artifact. When the signal-to-noise ratio is low, the coherence of the original desired signal will be completely destroyed by strong interference noise, and thus erroneously filtered out as noise by the symbol coherence coefficient beamformer, resulting in severe signal loss. The traditional solution reduces the influence of the coherence coefficient on the background quality by reducing the fluctuation degree of the sign coherence coefficient value, but the performance of the algorithm on the resolution is also limited, so that the better balance on the comprehensive imaging quality is difficult to achieve.

In summary, there is a need for a beam forming algorithm that can not only maintain the original resolution performance of the symbol coherence coefficient, but also greatly improve the background quality of strong speckles and solve the problem of image distortion, so as to comprehensively improve the comprehensive imaging quality of the ultrasound algorithm.

Disclosure of Invention

In view of this, the present invention aims to provide a high-robustness symbolic coherence coefficient ultrasonic imaging method with a truncation factor, which overcomes the problem that the conventional symbolic coherence coefficient algorithm is difficult to consider both the image background quality and the imaging resolution, and performs truncation threshold coefficient compensation on a weak coherence signal while maintaining enhancement on a strong coherence signal, so as to ensure that the image resolution is improved, substantially improve the imaging background quality, and improve the comprehensive imaging effect of the ultrasonic algorithm.

In order to achieve the purpose, the invention provides the following technical scheme:

a high robustness symbol coherence coefficient ultrasonic imaging method with truncation factors specifically comprises the following steps:

s1: preprocessing echo signals received by the ultrasonic array elements to obtain processed ultrasonic echo data, and storing the data obtained by each transceiving aperture into a data table A;

s2: extracting the symbol values of the echo data in each single-transmitting and full-receiving mode, and sequentially storing the symbol values in a data table B_signPerforming the following steps;

s3: under the synthetic aperture mode, calculating time domain symbol coherence coefficients corresponding to each transmitting array aperture under the single-transmitting and full-receiving mode according to the fluctuation characteristics of the ultrasonic echo symbol values, and sequentially obtaining a symbol coherence coefficient table;

s4: calculating the mean value of the symbol coherent coefficient table under each transmitting aperture as the truncation threshold SATC of the current symbol coherent coefficient table_sign；

S5: utilizing the truncation threshold to perform truncation processing on the echo symbol coherence coefficient, reserving the symbol coherence coefficient of the strong coherence part, and performing compensation optimization on the symbol coherence coefficient of the weak coherence part to obtain a truncated symbol coherence coefficient table TSCF;

s6: weighting the output of a delay superposition beam former formed by echo waves to sequentially obtain single-frame imaging subgraphs in a single-transmission and full-reception mode;

s7: and (3) carrying out spatial compounding on a plurality of imaging subgraphs in the single-shot full-receiving mode to obtain a final ultrasonic imaging result of the high-robustness symbol coherence coefficient beam former with the truncation factor.

Optionally, in S1, the processing the echo signal received by the ultrasound array element includes: amplifying, AD converting, noise filtering, and storing data obtained by each transceiving aperture into a number table A, wherein A is a three-dimensional number table with dimension of D multiplied by M multiplied by N, D represents the total sampling time number of echo waves, N represents the number of transmitting apertures, and M represents the number of receiving apertures; decomposing the detection area into Q multiplied by H pixel points, and sequentially calculating the focusing delay of each receiving and transmitting aperture to each detection point of the detection area as follows:

wherein f is_sRepresenting the sampling frequency, t_offIndicating the transmission of ultrasonic waves from the beginning to the firstThe time interval of receiving the echo, c represents the propagation speed of the ultrasonic wave in the medium of the detection region, q represents the longitudinal serial number of the pixel point in the detection region, h represents the transverse serial number of the pixel point in the detection region, m represents the serial number of the receiving aperture, and n represents the serial number of the transmitting aperture; x (q, h), x (0, m), x (0, n), y (q, h), y (0, m), y (0, n) respectively represent the abscissa and ordinate of the point (q, h) (0, m) (0, n); Δ (q, h, m, n) represents the amount of delay required by the receive aperture m at the current sampling instant when the pixel point (q, h) is detected and the transmit aperture is n.

Optionally, in S2, symbol values of echo data in each single-transmission full-reception mode are extracted and sequentially stored in the number table B_signIn (1), namely:

wherein, A (delta, m, n) represents the delayed data obtained by the receiving aperture m when the target pixel point (q, h) is detected and the transmitting aperture is n; b is_sign(Δ, m, n) represents symbol values of the delayed data obtained by the receiving aperture m when the target pixel point (q, h) is detected and when the transmitting aperture is n.

Optionally, in the S3, in the synthetic aperture mode, the time domain symbol coherence coefficient corresponding to each transmit array aperture in the single-transmit full-receive mode is calculated according to the fluctuation characteristic of the ultrasonic echo symbol value, and a symbol coherence coefficient table is sequentially obtained:

SCF_nand (q, h) represents the echo symbol coherence coefficient corresponding to the pixel point (q, h) in the detection region under the nth transmitting aperture, and the number N of the transmitting apertures is equal to the number M of the receiving apertures.

Optionally, in S4, the mean value of the symbol coherence coefficient table under each transmit aperture is obtained as the truncation threshold SATC of the current symbol coherence coefficient table_sign：

Wherein, SATC_sign(n) a truncation threshold representing a table of symbol coherence coefficients at the nth transmit aperture; and Q multiplied by H represents the total number of pixel points in the detection rectangular area.

Optionally, in S5, the truncation threshold is used to perform truncation processing on the echo symbol coherence coefficient, retain the symbol coherence coefficient of the strong coherent part, and perform compensation optimization on the symbol coherence coefficient of the weak coherent part, so as to obtain a truncated symbol coherence coefficient table TSCF:

TSCF_n(q,h)＝max(SATC_sign(n)，SCF_n(q,h))

TSCF_n(q, h) denotes the sign coherence coefficient of the nth transmit aperture with a truncation factor at the pixel point (q, h), SCF_n(q, h) represents the original symbol coherence coefficient, SATC, of the nth transmit aperture at pixel point (q, h)_sign(n) represents a symbol coherence coefficient truncation threshold at the nth transmit aperture; max (·) represents the maximum value solving function.

Optionally, in S6, the outputs of the delay superposition beam former formed by the echoes are weighted, so as to sequentially obtain a single-frame imaging sub-graph in the single-transmit and full-receive mode:

whereinRepresenting the output gray value of a pixel point (q, h) in a detection area of a beam former based on a symbol coherence coefficient TSCF with a truncation factor under the nth transmitting aperture, and G (q, h) representing the output gray value of a pixel point (q, h) in the detection area of an original beam former DAS; TSCF_nAnd (q, h) represents the symbol coherence coefficient of the nth transmitting aperture with the truncation factor on the pixel point (q, h).

Optionally, in S7, performing spatial compounding on the imaging subgraph in the single-shot full-receiving mode to obtain a final ultrasound imaging graph:

wherein, GZ_TSCF(q, h) represents the final output gray value of the pixel point (q, h) based on the beam former of the symbol coherence coefficient TSCF with the truncation factor in the synthetic aperture mode;and (3) under the nth transmitting aperture, the output gray value of a pixel point (q, h) in the detection region based on a beam former of a symbol coherence coefficient TSCF with a truncation factor is represented.

The invention has the beneficial effects that: compared with the existing symbol coherence coefficient algorithm, the method provided by the invention retains the high-resolution performance of the method on the strong scattering target point, and can effectively avoid signal loss under the environment of strong interference of the weak target. The invention can improve the resolution of the algorithm and avoid the generation of black area artifacts, thereby greatly improving the image background imaging quality, obtaining ideal comprehensive imaging effect and effectively solving the problem that the resolution, contrast and strong speckle background quality of the traditional coherence coefficient algorithm can not be considered at the same time.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.

Drawings

For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a flow chart of an implementation of a beamformer for a symbol coherence coefficient TSCF with a truncation factor;

FIG. 2 is a comparison graph of the multi-spot imaging results of 3 algorithms; FIG. 2(a) is a result of multi-spot imaging of DAS by the time-delay superposition algorithm; FIG. 2(b) is a multi-spot imaging result of a conventional sign coherence coefficient algorithm SCF; FIG. 2(c) is a multi-spot imaging result of a truncated symbolic coherence coefficient algorithm TSCF;

FIG. 3 is a plot of the target lateral resolution for multi-spot imaging of 50mm depth points for 3 algorithms;

FIG. 4 is an imaging of geabr0 for the 3 algorithms; FIG. 4(a) is a diagram of the imaging result of the time-lapse superposition algorithm DAS, geabr 0; FIG. 4(b) is the result of the geobr 0 imaging of the conventional symbolic coherence coefficient algorithm SCF; FIG. 4(c) is a result of a geobr 0 imaging of a truncated symbolic coherence coefficient algorithm TSCF;

figure 5 is a plot of the lateral resolution of the 3 algorithms at a depth of 77.5mm in the imaging plot of geabr 0.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.

Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.

Referring to fig. 1 to 5, fig. 1 is a flowchart of a method according to the present invention, and as shown in fig. 1, a preferred method for high robustness symbolic coherence coefficient ultrasonic imaging with truncation factor of the present invention includes the following steps:

step S1: the echo signal received by the ultrasonic array element is processed, which mainly comprises: amplifying, AD converting, noise filtering, and storing data obtained by each transceiving aperture into a number table A, wherein A is a three-dimensional number table with dimension of D multiplied by M multiplied by N, D represents the total sampling time number of echo waves, N represents the number of transmitting apertures, and M represents the number of receiving apertures; decomposing the detection area into Q multiplied by H pixel points, and sequentially calculating the focusing delay of each receiving and transmitting aperture to each detection point of the detection area as follows:

wherein f is_sRepresenting the sampling frequency, t_offThe time interval from the beginning of transmitting ultrasonic waves to the first time of receiving the echo is represented, c represents the propagation speed of the ultrasonic waves in a medium of a detection region, q represents the longitudinal serial number of a pixel point in the detection region, h represents the transverse serial number of the pixel point in the detection region, m represents a receiving aperture serial number, and n represents a transmitting aperture serial number; x (q, h), x (0, m), x (0, n), y (q, h), y (0, m), y (0, n) respectively represent the abscissa and ordinate of the point (q, h) (0, m) (0, n); Δ (q, h, m, n) represents the amount of delay required by the receive aperture m at the current sampling instant when the pixel point (q, h) is detected and the transmit aperture is n.

Step S2: extracting eachThe symbol values of the echo data in the single-transmitting and full-receiving mode are sequentially stored in a data table B_signIn (1), namely:

where a (Δ, m, n) represents delayed data obtained by the receiving aperture m when the target pixel point (q, h) is detected and when the transmitting aperture is n. B is_sign(Δ, m, n) represents symbol values of the delayed data obtained by the receiving aperture m when the target pixel point (q, h) is detected and when the transmitting aperture is n.

Step S3: under the synthetic aperture mode, calculating time domain symbol coherence coefficients corresponding to all transmitting array apertures under the single-transmitting and full-receiving mode according to the fluctuation characteristics of the ultrasonic echo symbol values, and sequentially obtaining a symbol coherence coefficient table:

SCF_nand (q, h) represents the echo symbol coherence coefficient corresponding to the pixel point (q, h) in the detection region under the nth transmitting aperture, and the number N of the transmitting apertures is equal to the number M of the receiving apertures.

Step S4: calculating the mean value of the symbol coherent coefficient table under each transmitting aperture as the truncation threshold SATC of the current symbol coherent coefficient table_sign：

Wherein, SATC_sign(n) represents the truncation threshold of the symbol coherence coefficient table at the nth transmit aperture. And Q multiplied by H represents the total number of pixel points in the detection rectangular area.

Step S5: the truncation threshold is utilized to perform truncation processing on the echo symbol coherence coefficient, the symbol coherence coefficient of the strong coherent part is reserved, the symbol coherence coefficient of the weak coherent part is compensated and optimized, and a truncated symbol coherence coefficient number table TSCF is obtained:

TSCF_n(q,h)＝max(SATC_sign(n)，SCF_n(q,h))

TSCF_n(q, h) denotes the sign coherence coefficient of the nth transmit aperture with a truncation factor at the pixel point (q, h), SCF_n(q, h) represents the original symbol coherence coefficient, SATC, of the nth transmit aperture at pixel point (q, h)_sign(n) represents the symbol coherence coefficient truncation threshold at the nth transmit aperture. max (·) represents the maximum value solving function.

Step S6: weighting the output of a delay superposition beam former formed by echo waves to sequentially obtain a single-frame imaging subgraph in a single-transmission full-receiving mode:

whereinAnd G (q, h) represents the output gray value of the original beam former DAS at the pixel point (q, h) of the detection area based on the beam former TSCF with the truncation factor under the nth transmitting aperture. TSCF_nAnd (q, h) represents the symbol coherence coefficient of the nth transmitting aperture with the truncation factor on the pixel point (q, h).

Step S7: carrying out spatial compounding on the imaging subgraph in the single-shot full-receiving mode to obtain a final ultrasonic imaging graph:

wherein, GZ_TSCF(q, h) represents the final output gray value at pixel point (q, h) of the beamformer based on the symbol coherence coefficient TSCF with the truncation factor in the synthetic aperture mode.To representAnd under the nth transmitting aperture, outputting gray values of pixel points (q, h) in the detection region by a beam former based on a symbol coherence coefficient TSCF with a truncation factor.

And (3) verification experiment:

field II is an ultrasonic experimental simulation platform developed by Denmark university of Engineers based on acoustic principle, and has been widely accepted and used in theoretical research. In order to verify the effectiveness of the algorithm, a Field II is utilized to image point scattering targets, sound absorption spots and strong speckles which are commonly used in ultrasonic imaging, and actual experimental data is utilized to carry out an imaging contrast experiment. In the multi-spot imaging simulation experiment, a row of 3 scattering point targets with the transverse positions at the center of 0mm and the longitudinal positions at the depths of 32.5mm, 50mm and 67.5mm are arranged, and two scattering point targets are additionally arranged at the positions of 50mm in the longitudinal direction and +/-5 mm in the transverse direction and are used for observing the transverse resolution of each algorithm, a synthetic aperture focusing mode is adopted, and the imaging dynamic range of an image is set to be 60 dB. Meanwhile, in the spot medium, two echolucent cysts with the radius of 3mm are arranged, the circle centers are respectively positioned at (-5mm, 40mm), (5mm, 50mm), and two strong speckles with the radius of 3mm are arranged, the circle centers are positioned at (5mm, 40mm) and (-5mm, 50 mm). The amplitude ratio of the scattering spot between the massive cyst and the background was 10 times, and the amplitude ratio between the anechoic cyst and the background was 40 times. The central frequency of array elements adopted by a Geabr0 data experiment is 3.33MHz, the number of the array elements is 64, the distance is 0.2413mm, the sampling frequency is 17.76MHz, the sound velocity is 1500m/s, and the imaging dynamic range is 60 dB.

And performing contrast imaging experiments on the three experimental targets by adopting a time delay superposition algorithm (DAS), a symbol coherence coefficient (SCF) and a symbol coherence coefficient (TSCF) with a truncation factor. FIG. 2 is a comparison graph of multi-spot imaging results of 3 algorithms, and FIG. 2(a) is the multi-spot imaging result of DAS (delayed addition and superposition algorithm); FIG. 2(b) is a multi-spot imaging result of a conventional sign coherence coefficient algorithm SCF; fig. 2(c) is a multi-spot imaging result of the truncated sign coherence coefficient algorithm TSCF. As can be seen from fig. 2, the DAS algorithm has the worst imaging quality and the lowest resolution, and compared with the other 2 algorithms, the side lobe artifact is significantly reduced and the resolution is significantly improved in the SCF algorithm compared to the DAS algorithm, but the background has significant distortion. The TSCF algorithm gives consideration to the improvement of the resolution contrast ratio of the algorithm and the background quality of the algorithm, and effectively solves the problem of black area artifacts existing in the SCF algorithm. Compared with the DAS algorithm, the TSCF algorithm has clearer point target resolving power and fewer in-class artifacts. Compared with the CF algorithm, the TSCF algorithm effectively improves the background imaging effect under the condition of keeping the resolution basically the same, and the comprehensive imaging performance is obviously improved.

FIG. 3 is a plot of the target transverse resolution for 50mm depth spot imaging for 3 algorithms, measured at-6 dB full width at half maximum (FWHM) value data as shown in Table 1. As can be seen from fig. 3 and table 1, the DAS has the lowest lateral resolution of 3 algorithms at different depths. The resolution of the SCF algorithm and the TSCF algorithm is significantly higher than the DAS algorithm. In addition, the TSCF algorithm is substantially the same as the SCF in resolution, and thus the TSCF algorithm may fully preserve the resolution advantage of the SCF in terms of resolution.

TABLE 1 FWHM contrasts of-6 dB for 3 algorithms at different depths in the multispot imaging simulation

Table 2 gives the background imaging index contrast in the multi-spot imaging experiment. According to the calculation, the real contrast of the dark spot should be 32.05, and it can be seen that the CR value of TSCF is closer to the real value and is significantly better than SCF in CNR. And the background variance SD and speckle signal-to-noise ratio of the TSCF are obviously improved compared with the SCF.

TABLE 2 comparison of imaging performance indices of different imaging algorithms for multi-spot imaging simulation

Fig. 4 shows a geobr 0 experimental imaging chart of 3 algorithms, and fig. 4(a) shows the imaging result of geobr 0 of DAS, which is a time-delay superposition algorithm; FIG. 4(b) is the result of the geobr 0 imaging of the conventional symbolic coherence coefficient algorithm SCF; fig. 4(c) is a result of geobr 0 imaging by the truncated sign coherence coefficient algorithm TSCF. As can be seen from FIG. 4, compared with other algorithms, the DAS algorithm has the worst imaging effect, the spot is seriously interfered by surrounding scattering points, a large number of artifacts are generated, the outline of the circular spot is unclear, and the size is inaccurate. Compared with DAS, the SCF algorithm has great improvement on side lobe suppression, but the background of the algorithm is also darkened, the image background distortion condition is clear, and the imaging robustness is poor. Compared with the SCF, the TSCF has the advantages that the TSCF obviously improves the background quality, has better dark spot background quality and has better imaging effect while keeping the SCF sidelobe suppression capability. And the resolution and contrast are also improved very obviously compared with the DAS. Table 3 shows a comparison of the imaging performance indicators of the different imaging algorithms geabr 0.

TABLE 3 comparison of imaging Performance indicators for different imaging algorithms geabr0

As can be seen from table 3, the DAS algorithm performed poorly overall, but the background robustness was stronger than the SCF algorithm. Whereas the SCF algorithm suffers from the very significant drawbacks in the SD and snr metrics. Compared with the traditional algorithm, the TSCF can not only keep good CR and CNR, but also greatly improve the related indexes SD and sSNR of background imaging. In conclusion, the TSCF algorithm can obtain better spot imaging effect compared with other traditional algorithms.

Figure 5 shows a lateral resolution plot of the 3 algorithms at a depth of 77.5mm in the imaging plot of geabr 0. It can be seen that the resolution of the DAS algorithm is obviously insufficient, the SCF greatly improves the resolution on the basis of the DAS, and greatly reduces the main lobe width, while the TSCF algorithm completely retains the resolution advantage of the SCF algorithm without sacrificing the imaging resolution due to the improvement of the background quality. Therefore, TSCF is significantly superior to conventional beamforming methods as a whole.

Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.