CN113177992B - Efficient synthetic aperture ultrasonic imaging method - Google Patents

Abstract

The invention discloses a high-efficiency synthetic aperture ultrasonic imaging method which comprises two-step synthetic aperture ultrasonic beam forming. The first step is similar to the superposition of seismic data, and the original three-dimensional channel data of the synthetic aperture ultrasound is subjected to delay accumulation to obtain the estimation of self-excited self-received two-dimensional RF data, so that the compression of the data is realized. And secondly, performing post-stack migration similar to the seismic data, and performing secondary beam forming on the two-dimensional RF data obtained in the first step by using a Fourier domain imaging method to obtain a final imaging result. The invention realizes the compression of the transmission data and reduces the calculation amount of beam forming.

Description

Efficient synthetic aperture ultrasonic imaging method

Technical Field

The invention belongs to the field of medical ultrasonic imaging, relates to a method for reducing data transmission quantity and imaging calculation quantity of synthetic aperture ultrasound, and particularly relates to a high-efficiency synthetic aperture ultrasound imaging method.

Background

Synthetic aperture ultrasound technology enables dynamic focusing of a transmitting unit and a receiving unit, and is a technology that effectively improves resolution and contrast of an ultrasound image, and is described in detail in, for example, document 1(Jensen, j.a., Nikolov, s.i., Gammelmark, k.l., & Pedersen, M.H, (2006). The synthetic aperture ultrasound transmits signals by one array element, all the array elements receive signals simultaneously, and after all the array elements transmit and receive all the signals in sequence, all the channel data are added by using a beam forming technology to obtain an imaging result, so that the challenges of huge data volume to be transmitted and large imaging calculation amount are faced, and the frame rate of an imaged ultrasonic video is low. In view of the above problems, many solutions have been proposed, which mainly include three categories:

1) method based on image compression. The method is to compress the original channel data of the ultrasound at the sensor end (front end) by using an image (video) compression technology, thereby reducing the transmitted data volume. The compressed data is transmitted to the imaging end (back end), decompressed to obtain the original channel data, and then synthetic aperture Ultrasound imaging is performed, so that the amount of calculation of imaging cannot be reduced, and the compression and decompression operations require additional time and bring about a decrease in the quality of the imaged image, such as documents 2(Li, y.f., & Li, P.C (2012) and ultrasonic imaging using data. ieee transformations on information technology in Biomedicine,16(3),308 and 313), 3 (chemical, p.w., shell, c.c. & Li, P.C. (2012), MPEG compression of the compressed RF channel data for a Real-time software-based imaging system, ieee transformations, transfer, calibration, k, and coding, 7, Real-time analysis, 7, Real-time coding, 7, parallel, 18(10), 3314).

2) A method based on compressed sensing. The method reduces the array element emission times by changing the acquisition mode, improves the data acquisition frame rate and reduces the acquired data volume. This kind of method needs to reconstruct the original Synthetic Aperture channel data from the data collected by Compressed Sensing, is an underdetermined ill-conditioned problem, needs to be solved by using nonlinear optimization technique, has long computation time, and is not currently available for real-time imaging, such as described in document 5(Liu, J., He, Q., & Luo, J. (2016). A Compressed Sensing equation for Synthetic transmitted imaging. IEEE Transactions on medial imaging,36(4), 878-.

3) A virtual source based approach. The method comprises the steps of performing beam forming in two steps, wherein in the first step, beam forming is performed on two-dimensional channel data obtained by sound wave emission each time by using the sound wave propagation time from a virtual source to a receiving array element as time delay, and a one-dimensional RF signal passing through a virtual source straight line is obtained. Performing beam forming on channel data obtained by transmitting all sound waves in a first step, and compressing an original three-dimensional array signal into a two-dimensional RF signal; second, the two-dimensional RF signals obtained in the first step are subjected to second imaging by delay accumulation (for example, document 7: Kortbek, j., Jensen, j.a., & Gammelmark, K.L. (2013). Sequential beamforming for synthetic imaging. ultrastronics, 53(1),1-16) or fourier domain imaging method (for example, document 8: Vos, h.j., van new, p.l., Mota, m.m., Verweij, m.d., van der Steen, a.f., Volker, A.W. (2015). F-k domain imaging for synthetic imaging Sequential beamforming. ieee beamforming for ultrasound on filters, ferroelectronics, frequency and control, 63-60), and finally, beam forming (71-71). The virtual source technology not only realizes the compression of transmission data, but also reduces the calculation amount of beam forming.

Such as document 8, document 9(Albulayli, M., & Rakhmatov, D. (2018), Fourier Domain Depth analysis for Plane-Wave Ultrasound Imaging, IEEE transactions on Ultrasound, and frequency control,65(8), 1321. A. 1333), document 10 (this, D., & Bonomi, E. (2020), Seismic Imaging for Medical Ultrasound analysis, physical Review, 14(3),034020), document 11(Ali, R., Hyun, D., & Dahl, J.J. (September) Seismic analysis, Medium, D., & Dahly, J.J. (IEEE, separation) Application software to Ultrasound sample analysis, Medium, and IEEE for Imaging, IEEE transaction system for general in, IEEE transaction, 1. 12. Application for general. Application of Ultrasound Imaging, IEEE transaction, 1. 12. for Imaging, IEEE transaction, and IEEE transaction, for Imaging, in the field of Ultrasound Imaging, and Ultrasound Imaging, for general use of Seismic data. Document 12 (muyong, chenomo, li seifu, liu, kingdom, authored by 2007, seismic data processing methods, oil industry publishers) describes a seismic imaging concept that stacks seismic data before post-stack migration.

In summary, the method based on image compression in the prior art has a large amount of calculation and reduces the image quality; the method based on compressed sensing needs to adopt a nonlinear optimization technology to solve, has long calculation time, and cannot be used for real-time imaging at present; the method based on the virtual source has relatively advantages, but how to realize the compression of the transmission data and reduce the calculation amount of beam forming is realized, and the method has very important practical significance for providing a new imaging method for a rapid synthetic aperture ultrasonic imaging system.

Object of the Invention

The invention aims to solve the problems in the prior art and provides a method for simultaneously reducing the data transmission quantity and the imaging calculation quantity of synthetic aperture ultrasound, namely, an efficient synthetic aperture ultrasound imaging method is provided, and synthetic aperture ultrasonic beams are divided into two steps, wherein the first step is similar to the superposition of seismic data, the original three-dimensional channel data of the synthetic aperture ultrasound is subjected to delay accumulation to obtain the estimation of self-excited self-received (single array element transmits and receives) two-dimensional RF data, and the data compression is realized; and secondly, performing post-stack migration similar to the seismic data, and performing secondary beam forming on the two-dimensional RF data obtained in the first step by using a Fourier domain imaging method to obtain a final imaging result.

Disclosure of Invention

The invention provides a synthetic aperture ultrasonic imaging method, which carries out beam forming on three-dimensional channel data of original synthetic aperture ultrasonic in two steps, and comprises the following steps:

step 1: forming a beam on the sensor end by a first-stage beam former by adopting a delay accumulation method; wherein, the three-dimensional channel data acquired by synthetic aperture ultrasound is recorded as d (x)_t,x_rT), wherein x_tBeing coordinates of transmitting array elements, x_rThe coordinates of the receiving array elements are shown, and t is the two-way propagation time of the sound waves; for each transmit-receive array element pair (x)_t,x_r) From the center point coordinate x_mThe distances h to the transmitting and receiving elements are equal, i.e. x_m＝(x_t+x_r)/2，h＝(x_t-x_r)/2；

For each transmit-receive array element pair (x)_t,x_r) Calculating delay time tau by using its correspondent h and given acoustic wave propagation speed v, making delay accumulation to obtain self-excited self-received two-dimensional RF data estimation, i.e. result l output by first-stage beam-forming device₁(x_m,t)＝B₁{d(x_t,x_rT)) }, in which B₁{ } denotes a first-stage beamformer; the process of calculating the delay time tau by using the corresponding h and the given sound wave propagation speed v is shown as the formula (1):

wherein, t₀＝z_pV, imaging point coordinate is (x)_p，z_p)，x_p＝x_mAll transmit-receive array element pairs (x)_t，x_r) Of (t)₀H) the value is finite, and all possible (t) values are calculated in advance₀H) and storing the delay in the memory;

step 2: forming a beam at the imaging port by a second stage beamformer; wherein, using a given sound wave propagation velocity v, a Fourier domain imaging method is adopted to obtain a B ultrasonic image, i.e./, output by a second-stage beam former₂(x_m,t)＝B₂{l₁(x_mT) }, in which B₂{ } denotes the second stage beamformer; further comprising the substeps of:

step 21: to l₁(x_mT) performing a two-dimensional Fourier transform to obtain Fl₁(k，ω₁)；

Step 22: for each fixed k, using one-dimensional interpolation, from Fl₁(k，ω₁) Obtaining Fl₂(k，ω₂) Wherein, in the step (A),

step 23: for Fl₂(k，ω₂) Performing two-dimensional inverse Fourier transform to obtain l₂(x_m，t)。

Drawings

Fig. 1 is a flow chart of a synthetic aperture ultrasound imaging method according to the present invention.

Figure 2 is a schematic diagram of synthetic aperture ultrasound propagation.

FIG. 3 is a comparison of a focused B-mode ultrasound received by one embodiment of the present invention and a conventional method: 3a is traditional dynamic receiving focusing B-ultrasonic; and 3B is the synthetic aperture dynamic transmitting receiving focusing B-ultrasonic obtained by the invention.

Detailed Description

In order to explain the technical solution of the present invention in more detail, the following detailed description of the present invention is provided with reference to the accompanying drawings, and it should be noted that the detailed description is only for illustrative purposes and not for limiting the present invention.

The flow chart of the synthetic aperture ultrasonic imaging method is shown in fig. 1, and fig. 2 shows a synthetic aperture ultrasonic propagation schematic diagram, which comprises a propagation path schematic diagram of information from a transmitting array element, a central point, a receiving array element and an imaging point.

The method of the invention is divided into two steps of imaging, comprising:

(1) first step beam forming:

the first step of beam forming is completed at the sensor end (front end) by adopting a time delay accumulation method.

Recording three-dimensional channel data acquired by synthetic aperture ultrasound as d (x)_t，x_rT), wherein x_tBeing coordinates of transmitting array elements, x_rThe coordinates of the receiving array elements are shown, and t is the two-way propagation time of the sound waves;

FIG. 2 shows a synthetic aperture ultrasound propagation diagram, including a diagram of the propagation paths of information from the transmit array element, the center point, the receive array element, the imaging point, for each transmit-receive array element pair (x)_t,x_r) And the coordinate of the center point is marked as x_m，x_m＝(x_t+x_r) And/2, the distances from the center point to the transmitting and receiving array elements are equal, and are recorded as h ═ x_t-x_r)/2；

In the conventional synthetic aperture single step beamforming method, for each transmit-receive array element pair (x)_t,x_r) Imaging point (x)_p,z_p) The method falls into a given two-dimensional imaging area, the calculation amount of beam forming is large, all three-dimensional channel data are required to be transmitted when the beam forming is carried out at an imaging end, and the data amount is large.

The invention firstly assumes a transmitting-receiving array element pair (x)_t,x_r) Imaging point (x) of_p,z_p) Falling only on the dotted line passing through the center point shown in FIG. 2, i.e. x_p＝x_mCalculating the delay time by using h corresponding to the central point and a given sound wave propagation speed v, as shown in formula (1):

in the formula, t₀＝z_pAnd/v. Due to all transmit-receive array element pairs (x)_t,x_r) Of (t)₀H) the value is finite, and all possible (t) values are calculated in advance₀And h) time delay and storing in a memory, thereby achieving the purpose of reducing the calculated amount.

Performing delay accumulation by using the time delay obtained by the formula (1) to obtain a self-excited self-received two-dimensional RF data estimation (namely a first-stage beam forming result) l₁(x_m,t)＝B₁{d(x_t,x_rT)) }, in which B₁{ … } denotes a first stage beamformer;

through the first-step beam forming, the first-stage beam forming is completed, three-dimensional channel data are compressed into two-dimensional self-excited self-receiving data, and the transmission quantity of the data is greatly reduced.

(2) And a second step of beam forming:

the second step of beam forming is completed at the imaging end (back end), and the method of Fourier domain imaging is adopted, and comprises the following steps:

first, for I₁(x_mT) performing a two-dimensional Fourier transform to obtain FI₁(k，ω₁) (ii) a Then, for each fixed k, the FI is interpolated by one dimension₁(k，ω₁) Obtaining FI₂(k，ω₂) Wherein, in the step (A),

last to FI₂(k，ω₂) Performing two-dimensional inverse Fourier transform to obtain I₂(x_mT), i.e. l₂(x_m,t)＝B₂{l₁(x_mT) }, in which B₂{ … } denotes a second stage beamformer.

Simulation result of experiment

Figure 3 shows the experimental results of the present invention on synthetic aperture ultrasound data. Fig. 3a shows a conventional B-mode ultrasound image, and fig. 3B shows a B-mode ultrasound image of a synthetic aperture ultrasound image obtained by the method proposed by the present invention. Compared with the traditional B-mode ultrasonic acquisition method, the two-step beam forming imaging method provided by the invention has the advantages that the data transmission quantity and the imaging frame rate are equivalent, and as can be seen from the figure 3, the quality of the B-mode ultrasonic image obtained by the invention is superior to that of the traditional B-mode ultrasonic image.

Claims (1)

1. A synthetic aperture ultrasonic imaging method is used for carrying out beam forming on three-dimensional channel data of original synthetic aperture ultrasonic in two steps, and is characterized by comprising the following steps:

step 1: forming a beam on the sensor end by a first-stage beam former by adopting a delay accumulation method; wherein, the three-dimensional channel data acquired by synthetic aperture ultrasound is recorded as d (x)_t，x_rT), wherein x_tBeing coordinates of transmitting array elements, x_rThe coordinates of the receiving array elements are shown, and t is the two-way propagation time of the sound waves; for each transmit-receive array element pair (x)_t，x_r) From the center point coordinate x_mThe distances h to the transmitting and receiving elements are equal, i.e. x_m＝(x_t+x_r)/2，h＝(x_t-x_r)/2；

For each transmit-receive array element pair (x)_t，x_r) Calculating delay time tau by using its correspondent h and given acoustic wave propagation speed v, making delay accumulation to obtain self-excited self-received two-dimensional RF data estimation, i.e. result l output by first-stage beam-forming device₁(x_m，t)＝B₁{d(x_t，x_rT)) }, in which B₁{ } denotes a first stage beamformer; the process of calculating the delay time tau by using the corresponding h and the given sound wave propagation speed v is shown as the formula (1):

wherein, t₀＝z_pV, imaging point coordinate is (x)_p，z_p)，x_p＝x_mAll transmit-receive array element pairs(x_t，x_r) Of (t)₀H) the value is finite, and all possible (t) values are calculated in advance₀H) and storing the delay in the memory;

step 2: forming a beam at the imaging port by a second stage beamformer; wherein, using a given sound wave propagation velocity v, a Fourier domain imaging method is adopted to obtain a B ultrasonic image, i.e./, output by a second-stage beam former₂(x_m，t)＝B₂{l₁(x_mT) }, in which B₂{ } denotes the second stage beamformer; further comprising the substeps of:

step 21: to l is to₁(x_mAnd t) performing two-dimensional Fourier transform to obtain Fl₁(k，ω₁)；

Step 22: for each fixed k, using one-dimensional interpolation, from Fl₁(k，ω₁) Obtaining Fl₂(k，ω₂) Wherein, in the step (A),

step 23: for Fl₂(k，ω₂) Performing two-dimensional inverse Fourier transform to obtain l₂(x_m，t)。

Images