CN105411624A - Ultrasonic three-dimensional fluid imaging and speed measuring method - Google Patents

Abstract

The invention discloses an ultrasonic three-dimensional fluid imaging and velocity measurement method, the method comprising: step 1, adding or generating a fluid tracer in the flow field; step 2, using an ultrasonic array transducer to perform 3D scanning on the flow field , collecting ultrasonic original 3D radio frequency data; step 3, forming a 3D ultrasonic particle image sequence based on the collected and stored ultrasonic original 3D radio frequency data; step 4, calculating a flow field three-dimensional velocity distribution based on the 3D ultrasonic particle image sequence.

Description

An Ultrasonic Three-dimensional Fluid Imaging and Velocimetry Method

technical field

The invention relates to the technical field of ultrasonic particle image velocity measurement, in particular to an ultrasonic three-dimensional fluid imaging and velocity measurement method.

Background technique

Blood circulation is very important to maintain human life, and cardiovascular fluid mechanics has become the most active research in the development of biofluid mechanics and even biomechanics. In the early stage of cardiovascular disease, abnormal blood flow movement will lead to changes in blood flow velocity, shear force, vorticity and other parameters, which can be used as an important basis for early detection of cardiovascular disease and early warning of acute cardiovascular events. Due to the complex three-dimensional movement of blood in the blood vessels, the commonly used ultrasonic two-dimensional blood flow velocity measurement and imaging techniques (such as ultrasonic color Doppler) in medical clinics often cannot reflect the real blood flow information, so it is necessary to develop a three-dimensional flow field velocity measurement method.

In the patent application titled method and device for layered synchronous three-dimensional particle image velocimetry (application number: CN201310119595.8), the technical solution proposed is that the method for layered synchronous three-dimensional particle image velocimetry uses a prism splitting device to divide the incident The multi-color laser is dispersed into different color light sources, which are illuminated to the test area at the same time; the illuminated particle images show different color characteristics in different sections; a group of CCD cameras are set near the test area, and a certain camera is installed in front of each camera lens. A filter of a specific color is consistent with the color of the light source, so that the camera can only capture the section of the corresponding color; all cameras work at the same time, simultaneously acquire the particle images on different sections, and perform binary images on each section. Three-dimensional particle image analysis, correlation analysis of images between different sections, to obtain three-dimensional flow field information. However, this invention is based on optical lighting and is mainly used in fluid dynamics model tests and measurements. It can only be applied to transparent fluid dynamics model tests and measurements, and cannot be applied to three-dimensional fluid velocity measurement of non-transparent fluids (such as blood flow).

In the patent application titled 3D Ultrasonic Color Flow Imaging Using Grayscale Inversion (Application No.: CN200780037891.6), the invention uses an ultrasonic diagnostic imaging system to generate a 3D image of blood flow, which is both The location of the blood bank is depicted, which in turn depicts the flow rate. Specifically, the Doppler processor is used to process time-different signals from tissue and blood flow, so as to detect the movement of substances including blood cells and tissues in the image field. The Doppler processor operates on a population of temporally distinct samples from each location within the volume to be imaged to generate Doppler power, velocity, acceleration or an estimate of the variance. Since the ultrasonic Doppler technique can only obtain the fluid velocity in the direction of propagation of the ultrasonic beam, there is usually a large measurement error and cannot obtain the true three-dimensional velocity.

Contents of the invention

Aiming at the defects existing in the prior art, the present invention proposes an ultrasonic three-dimensional fluid imaging and velocity measurement method. Since ultrasonic waves have better penetration to optically non-transparent fluids (such as biological tissue and blood), it can be applied to non-transparent fluid. At the same time, the present invention proposes to spread certain fluid tracer particles (such as microbubbles) in the flow field. These tracer particles can better track the movement of the fluid, and the three-dimensional motion information of the particles can be captured by ultrasonic imaging equipment to obtain real The three-dimensional velocity distribution of the flow field.

In order to achieve the above object, an ultrasonic three-dimensional fluid imaging and velocity measurement method proposed by the present invention includes: step 1, adding or generating a fluid tracer in the flow field; step 2, using an ultrasonic array transducer to conduct 3D scanning, collecting ultrasonic original 3D radio frequency data; step 3, forming a 3D ultrasonic particle image sequence based on the collected and stored ultrasonic original 3D radio frequency data; step 4, calculating the flow field three-dimensional velocity distribution based on the 3D ultrasonic particle image sequence.

Further, in step 2, the ultrasonic array transducer is used to scan the flow field in 3D, and the original ultrasonic 3D radio frequency data is collected, including: using a two-dimensional array of ultrasonic transducer elements, and the emitted ultrasonic waves cover a three-dimensional space area, and obtain the ultrasonic echo of this area, and store the echo radio frequency signal of each point in the ultrasonic irradiation area to form the original 3D radio frequency data of ultrasound.

Further, in step 2, the ultrasonic array transducer is used to perform 3D scanning on the flow field, and the acquisition of ultrasonic original 3D radio frequency data includes: scanning with a one-dimensional array of ultrasonic transducer elements, A position detector is installed on the array to record the movement trajectory. The ultrasonic transducer array emits ultrasonic waves at each position and receives echoes to obtain 2D plane data. According to the movement trajectory and the 2D plane data at each position, the original 3D ultrasound is formed. RF data.

Further, scanning methods using a one-dimensional array of ultrasonic transducer elements include: parallel scanning, sectoral scanning, and arbitrary path scanning.

Further, in step 3, constructing a 3D ultrasonic particle image based on the collected and stored ultrasonic original 3D radio frequency data includes: analyzing and processing the radio frequency signal in the ultrasonic original 3D radio frequency data, extracting fundamental frequency or harmonic components, and generating brightness Mode ultrasonic image, according to the amplitude and phase of the radio frequency signal at each point, the brightness value at that point is obtained, and the ultrasonic brightness map in the three-dimensional space is constructed to form a 3D ultrasonic particle image sequence.

Further, in the brightness mode ultrasound image, each position has a specific brightness value, which is stored in the 3D data set and displayed as a three-dimensional image or a two-dimensional image of any slice, wherein the fluid trace in the flow field Agents exist in the form of bright spots.

Further, in step 4, based on the 3D ultrasonic particle image sequence, the calculation of the three-dimensional velocity distribution of the flow field includes: in the 3D ultrasonic particle image sequence, discretizing each three-dimensional ultrasonic particle image into a 3D cubic grid; Three-dimensional cross-correlation processing is performed on two three-dimensional ultrasonic particle images, and the displacement vector and velocity vector at each cubic grid position are calculated to obtain the three-dimensional velocity distribution in the flow field.

Further, the three-dimensional cross-correlation processing includes: selecting a cubic grid of the first image, calculating the cross-correlation index between the cubic grid and each cubic grid in the second image; determining the maximum cross-correlation index corresponding to the second image According to the position of the most matching cube grid in the second image, calculate the displacement vector and velocity vector at the position of the cube grid in the first image; repeat the above steps to calculate and obtain each cube in the first image in turn The displacement vector and velocity vector at the grid position.

The ultrasonic three-dimensional fluid imaging and velocity measurement method proposed by the present invention uses array ultrasonic transducers to collect ultrasonic images of the flow field in real time, and has the advantage of fast and high frame rate. Ultrasonic waves can be applied to non-transparent fluids due to their good penetrability to optically non-transparent fluids (such as biological tissue and blood). The present invention proposes to distribute fluid tracer particles in the flow field, track the fluid movement by the tracer particles, capture the three-dimensional motion information of the particles through ultrasonic imaging, and finally obtain the real three-dimensional velocity distribution of the flow field, which is different from the existing ultrasonic Doppler Compared with technology, speed measurement is more accurate.

Description of drawings

The drawings described here are used to provide further understanding of the present invention, constitute a part of the application, and do not limit the present invention. In the attached picture:

Fig. 1 is a flowchart of an ultrasonic three-dimensional fluid imaging and velocity measurement method according to an embodiment of the present invention.

2A-2D are schematic diagrams of four different ultrasonic 3D scanning and data acquisition methods according to an embodiment of the present invention.

Fig. 3 is a schematic flow chart of the construction and discretization of 3D ultrasonic particle images according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a 3D image cross-correlation process of a 3D ultrasonic particle image sequence according to an embodiment of the present invention.

detailed description

The technical means adopted by the present invention to achieve the intended invention purpose are further described below in conjunction with the drawings and preferred embodiments of the present invention.

Fig. 1 is a flowchart of an ultrasonic three-dimensional fluid imaging and velocity measurement method according to an embodiment of the present invention. Among them, the method includes:

Step S101, adding or generating a fluid tracer in the flow field. Specifically, fluid tracers can be added to the fluid to be tested, such as micron-sized bubbles, or tiny particles, tiny droplets, etc. Tracer particles are generated internally, e.g. hydrogen bubbles in water.

Fluid tracer particles are uniformly distributed in the flow field and follow the fluid motion. When the tracer particles are irradiated by ultrasonic waves, due to the acoustic impedance between the particles themselves and the surrounding medium, they will reflect and scatter the ultrasonic waves greatly, and the amplitude of the ultrasonic waves is large, which is displayed as a bright spot in the ultrasonic image. The area without tracer particles has a black background. This kind of bright spot ultrasound image on a black background is generally called an ultrasound particle image.

Step S102, using an ultrasonic array transducer to perform 3D scanning on the flow field to collect ultrasonic original 3D radio frequency data; the ultrasonic transducer array is used to transmit ultrasonic waves and receive echo signals.

Specifically, a two-dimensional array of ultrasonic transducer elements or a one-dimensional array of ultrasonic transducer elements may be used for scanning.

Using a two-dimensional array of ultrasonic transducer elements, the emitted ultrasonic waves cover a three-dimensional space area, and the ultrasonic echoes of this area are obtained, and the echo radio frequency signals of each point in the ultrasonic irradiation area are stored to form an ultrasonic original 3D RF data.

A one-dimensional array of ultrasonic transducer elements is used for scanning, and the scanning methods include: parallel scanning, sectoral scanning, and arbitrary path scanning. Install a position detector on the ultrasonic transducer array to record the movement trajectory. The ultrasonic transducer array emits ultrasonic waves at each position and receives echoes to obtain 2D plane data. According to the movement trajectory and the 2D plane data at each position , forming the original 3D radio frequency data of ultrasound.

Step S103, based on the collected ultrasonic original 3D radio frequency data, a 3D ultrasonic particle image sequence is formed.

Specifically, first, analyze and process the RF signal in the original 3D RF data of the ultrasound, extract the fundamental frequency or any harmonic component, and generate a brightness mode (B-mode) ultrasound image, according to the amplitude and phase of the RF signal at each point , obtain the brightness value at the point, construct the ultrasonic brightness map in the three-dimensional space, and form the 3D ultrasonic particle image sequence based on the uninterrupted multiple times of 3D data.

Wherein, the harmonic components include frequency division harmonics, overfrequency harmonics or second harmonics, but are not limited thereto.

In the brightness mode ultrasound image, each position has a specific brightness value, which is stored in the 3D data set and displayed as a three-dimensional image or a two-dimensional image of any slice, where the fluid tracer in the flow field exists in the form of a bright spot .

Step S104, based on the 3D ultrasonic particle image sequence, calculate the three-dimensional velocity distribution of the flow field.

Specifically, firstly, in the 3D ultrasonic particle image sequence, each three-dimensional ultrasonic particle image is discretized into a 3D cubic lattice;

Three-dimensional cross-correlation processing is performed on two adjacent three-dimensional ultrasonic particle images, and the displacement vector and velocity vector at the position of each cubic grid are calculated to obtain the three-dimensional velocity distribution in the flow field.

The specific method of the above-mentioned three-dimensional cross-correlation processing is as follows:

A cubic grid in the first image is selected, and a cross-correlation index (CrossCorrelationIndex, CCI) between the cubic grid and each cubic grid in the second image is calculated. Determine the cubic grid in the second image corresponding to the largest cross-correlation index as the best match, and calculate the displacement vector and velocity vector at the cubic grid position of the first image according to the position of the best-matched cubic grid in the second image. Repeat the above steps to sequentially calculate and obtain the displacement vector and velocity vector at each cube grid position in the first image, and finally obtain the three-dimensional velocity distribution in the flow field.

The ultrasonic three-dimensional fluid imaging and velocity measurement method proposed by the present invention is a micro-scale non-transparent fluid multi-dimensional flow field imaging and measurement method based on micro-ultrasonic particle image velocity measurement technology. The present invention includes the following key points:

1. Can identify and track the tracer in the flow field, and scan through the ultrasonic array transducer to scan in the field of view of the fluid of interest to obtain 3D brightness mode ultrasonic particle images, for continuous multi-frame (at least two frames) 3D Ultrasonic particle images are analyzed for particle images to obtain three-dimensional velocity vector distributions.

2. Accurate measurement of the three-dimensional velocity distribution of the flow field is obtained by tracking the tracer particles. The appropriate concentration of tracer particles is also determined based on the image characteristics of the analyzed ultrasonic images to ensure the speed measurement accuracy.

3. Use the ultrasonic array transducer to transmit ultrasonic waves to the flow field and receive echoes, collect 3D ultrasonic radio frequency data, and construct 3D ultrasonic particle images.

4. Construct 3D ultrasonic particle images, which can be based on the fundamental frequency component or harmonic component of ultrasonic radio frequency data.

5. Discretize each three-dimensional ultrasonic particle image into a 3D cubic grid, and use the 3D image cross-correlation algorithm to process the 3D ultrasonic particle image sequence to obtain the three-dimensional velocity distribution of the flow field.

The ultrasonic three-dimensional fluid velocity measurement and imaging method disclosed in the present invention can be applied to the velocity measurement of fast-flowing blood in the human vascular network, thereby obtaining rich hemodynamic information, including blood flow three-dimensional velocity distribution and shear force distribution. These precise three-dimensional blood flow information can be an important criterion for the prediction, diagnosis and treatment of cardiovascular diseases. At the same time, the technology disclosed in the present invention can also be used for three-dimensional fluid velocity measurement of other non-transparent fluids (such as industrial underdrains and non-transparent micro-flow fields).

In order to explain the above-mentioned ultrasonic three-dimensional fluid imaging and velocity measurement method more clearly, a specific embodiment will be described below. However, it should be noted that this embodiment is only for better illustrating the present invention, and does not constitute Invention of improper limitations.

In conjunction with step S101, a fluid tracer is dispensed. Ultrasonic three-dimensional blood flow velocimetry and imaging for human blood flow, through human intravenous injection of ultrasound-enhanced microbubbles.

The ultrasound contrast agent is a micron-sized bubble with a stable shell structure. When excited by ultrasound, the microbubbles will shrink and expand regularly with the periodic pressure changes of the sound waves. The introduction of ultrasound contrast agents has greatly improved the resolution of ultrasound imaging. Considering that the microbubble concentration will greatly affect the accuracy of image cross-correlation matching, before collecting 3D ultrasound data, a real-time evaluation method of microbubble concentration based on image texture matching will be used to evaluate whether the microbubble concentration is in the appropriate range. When the concentration of microbubbles is judged to be suitable, the acquisition of 3D ultrasound data is started. For details, see the paper Ultrasound Med. & Biol., 37(8): 1280-1291, 2011. The invention can also be applied to three-dimensional fluid velocity measurement of industrial large-scale fluid and micro-scale fluid. For these two applications, it is not necessary to add ultrasound contrast-enhanced microbubbles, and the device can generate bubbles inside the fluid as a fluid tracer.

Combined with step S102, ultrasonic 3D scanning and data acquisition of the region of interest in the flow field. Combined with FIG. 2A-FIG. 2D, it is a schematic diagram of four different ultrasonic 3D scanning and data acquisition methods. in,

The array shown in FIG. 2A is a two-dimensional array of ultrasonic transducer elements, and the emitted ultrasonic waves can cover a three-dimensional space area, and obtain ultrasonic echoes in this area. The echo radio frequency signals of each point in the ultrasonic irradiation area are stored to form 3D data.

Figures 2B-2D illustrate data acquisition using a one-dimensional array of ultrasound transducer elements with different scanning modalities. Scanning methods include parallel scanning (shown in FIG. 2B ), sectoral scanning (shown in FIG. 2C ), and arbitrary path scanning (shown in FIG. 2D ). A position detector is arranged on the ultrasonic transducer array for recording the movement trajectory of the probe, and the movement trajectory information is used for subsequent 3D image construction. Ultrasonic waves are transmitted at each position through the ultrasonic array and echoes are received to obtain data on a 2D plane, and then form 3D data from multiple 2D planes.

Combined with step S103, 3D ultrasonic particle image construction and discretization.

As shown in Figure 3, it is a schematic diagram of the construction and discretization process of 3D ultrasonic particle images. The ultrasonic array transducer emits ultrasonic waves and receives echoes, and stores the data of each point in the 3D space in the form of original ultrasonic radio frequency signals, that is, 3D ultrasonic radio frequency data. Data acquisition is performed continuously to form a 3D ultrasound radio frequency data sequence (1, 2, . . . , n).

Then, analyze and process the 3D ultrasound radiofrequency data. The fundamental frequency component or any harmonic component of the RF data can be extracted to generate a brightness mode (B-mode) ultrasound image. When microbubbles are used as flow field tracers, since the harmonic components of microbubbles are significantly higher than those of human tissues (such as blood vessel walls and muscles), high-contrast ultrasonic particle images can be formed using harmonic components. According to the amplitude and phase of the radio frequency signal at each point, the specific brightness value at the point is obtained, and the ultrasonic brightness map in the three-dimensional space is constructed to form a 3D ultrasonic particle image sequence. For each ultrasonic particle image in the sequence, it is discretized into cubic grids. The cube grid is the basic unit in the subsequent 3D image cross-correlation processing.

In conjunction with step S104, the three-dimensional velocity distribution of the flow field is calculated based on the 3D ultrasonic particle image sequence.

In the sequence of 3D ultrasonic particle images, each three-dimensional ultrasonic particle image is discretized into a 3D cubic lattice. The cubic grid is the basic unit, containing the ultrasound brightness image distribution for each location. The 3D image cross-correlation algorithm is used to process two adjacent 3D images in the image sequence, for example, 3D image ₁ at time t1 and 3D image ₂ at time t2 in FIG. 3 .

As shown in FIG. 4 , it is a schematic diagram of the 3D image cross-correlation process of the 3D ultrasonic particle image sequence. Select the cubic grid 1 of the 3D image 1, and set the three-dimensional coordinates of the cubic grid as the starting position. Calculate the cross-correlation index (CCI) between the cubic grid 1 and each cubic grid in the three-dimensional area of the entire 3D image 2 . As shown in Fig. 4, when the CCI value of the cubic grid 1 and the cubic grid 2 is the largest, it is considered that the matching degree of the image features of these two units is the highest. In this embodiment, the three-dimensional coordinates of the cubic grid 2 are the end positions. The displacement vector is obtained according to the positions of the two, and divided by the time difference (t ₁ -t ₂ ), the velocity vector and the velocity component scalars in the X, Y, and Z directions can be obtained. Three-dimensional cross-correlation matching is performed on the cubic grids of 3D image 1 and 3D image 2 in turn, and the fluid velocity at each cubic grid position can be obtained. By repeating the above steps, the three-dimensional velocity distribution in the flow field can be finally obtained.

The ultrasonic three-dimensional fluid imaging and velocity measurement method proposed by the present invention uses array ultrasonic transducers to collect ultrasonic images of the flow field in real time, and has the advantage of fast and high frame rate. Ultrasonic waves can be applied to non-transparent fluids due to their good penetrability to optically non-transparent fluids (such as biological tissue and blood). The present invention proposes to distribute fluid tracer particles in the flow field, track the fluid movement by the tracer particles, capture the three-dimensional motion information of the particles through ultrasonic imaging, and finally obtain the real three-dimensional velocity distribution of the flow field, which is different from the existing ultrasonic Doppler Compared with technology, speed measurement is more accurate.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (8)

1. An ultrasonic three-dimensional fluid imaging and velocity measurement method, is characterized in that, the method comprises: Step 1, adding or generating a fluid tracer in the flow field; Step 2, using an ultrasonic array transducer to perform 3D scanning on the flow field, and collecting ultrasonic original 3D radio frequency data; Step 3, based on the collected and stored ultrasonic original 3D radio frequency data, a 3D ultrasonic particle image sequence is formed; Step 4, based on the 3D ultrasonic particle image sequence, calculate the three-dimensional velocity distribution of the flow field. 2. The method according to claim 1, characterized in that, in step 2, the flow field is scanned in 3D by an ultrasonic array transducer, and the raw ultrasonic 3D radio frequency data is collected, comprising: Using a two-dimensional array of ultrasonic transducer elements, the emitted ultrasonic waves cover a three-dimensional space area, and the ultrasonic echoes of this area are obtained, and the echo radio frequency signals of each point in the ultrasonic irradiation area are stored to form an ultrasonic original 3D RF data. 3. The method according to claim 1, wherein in step 2, the flow field is scanned in 3D by an ultrasonic array transducer, and the original 3D radio frequency data of the ultrasonic wave is collected, comprising: A one-dimensional array of ultrasonic transducer elements is used for scanning, and a position detector is installed on the ultrasonic transducer array to record the movement trajectory. The ultrasonic transducer array emits ultrasonic waves at each position and receives echoes to obtain 2D plane data , according to the data of the motion trajectory and the 2D plane of each position, the original 3D radio frequency data of the ultrasound is formed. 4 . The method according to claim 3 , wherein the manner of scanning with a one-dimensional array of ultrasonic transducer elements comprises: parallel scanning, sectoral scanning, and arbitrary path scanning. 5. The method according to claim 1, wherein, in step 3, constructing a 3D ultrasonic particle image based on the collected and stored ultrasonic original 3D radio frequency data, comprising: Analyze and process the radio frequency signal in the original 3D radio frequency data of the ultrasound, extract the fundamental frequency or harmonic components, generate a brightness mode ultrasonic image, obtain the brightness value at the point according to the amplitude and phase of the radio frequency signal at each point, and construct a three-dimensional Ultrasound brightness maps in space, forming a 3D ultrasound particle image sequence. 6. The method according to claim 5, characterized in that, in the brightness mode ultrasonic image, each position has a specific brightness value, which is stored in the 3D data set, and is displayed in a three-dimensional image or a two-dimensional image of any slice. The image shows that the fluid tracer exists as bright spots in the flow field. 7. The method according to claim 1, wherein in step 4, based on the 3D ultrasonic particle image sequence, calculating the three-dimensional velocity distribution of the flow field includes: In the 3D ultrasonic particle image sequence, discretize each three-dimensional ultrasonic particle image into a 3D cubic lattice; Three-dimensional cross-correlation processing is performed on two adjacent three-dimensional ultrasonic particle images, and the displacement vector and velocity vector at the position of each cubic grid are calculated to obtain the three-dimensional velocity distribution in the flow field. 8. The method according to claim 7, wherein the three-dimensional cross-correlation processing comprises: Select a cube lattice of the first image, and calculate the cross-correlation index between the cube lattice and each cube lattice in the second image; Determine that the cubic lattice in the second image corresponding to the maximum cross-correlation index is the most matching, and calculate the displacement vector and the velocity vector at the cubic lattice position of the first image according to the position of the most matching cubic lattice in the second image; Repeat the above steps to sequentially calculate and obtain the displacement vector and the velocity vector at each cube grid position in the first image.