Pulse wave velocity estimation method and system based on intima-media thickness

Abstract

The invention provides a pulse wave velocity estimation method and system based on intima-media thickness, and the method comprises the steps: 1, collecting a high-frame-frequency image, and recognizing the position of a blood vessel wall in the high-frame-frequency image; 2, estimating the axial speed of the blood vessel wall; 3, when the axial speed of the blood vessel wall is maximum, the intima-media thickness is recognized according to the high-frame-frequency image, and the blood vessel wall is segmented according to the intima-media thickness; 4, estimating the pulse wave speed in a segmented manner to obtain the whole-segment average pulse wave speed; therefore, the pulse wave velocity measurement is more accurate, cardiovascular diseases such as atherosclerosis can be found and evaluated in the early stage, or the progress or rehabilitation condition of atherosclerosis can be evaluated in stages.

Description

Technical Field

[0001] The present invention relates to the technical field of medical image processing and physiological signal analysis, and in particular to a pulse wave velocity estimation method and system based on intima-media thickness. Background Art

[0002] Pulse Wave Velocity (PWV) is an important parameter for measuring arterial stiffness and is widely used in the early diagnosis and risk assessment of cardiovascular diseases;

[0003] However, traditional PWV measurement methods usually rely on body surface measurement, which is easily affected by the measurement environment and individual differences, and has low accuracy. With the development of ultrasound imaging technology, PWV measurement methods based on ultrasound images have gradually attracted attention, and the existing PWV measurement methods based on ultrasound images still have problems such as low automation and low accuracy.

[0004] Therefore, in order to overcome the above technical problems, the present invention provides a method and system for estimating pulse wave velocity based on intima-media thickness. Summary of the invention

[0005] The present invention provides a pulse wave velocity estimation method and system based on intima-media thickness, which is used to effectively identify the position of the blood vessel wall in the high frame rate image by acquiring a high frame rate image, thereby improving the automation of pulse wave velocity measurement, estimating the axial velocity of the blood vessel wall, and identifying the intima-media thickness according to the high frame rate image when the axial velocity of the blood vessel wall is the largest, and segmenting the blood vessel wall according to the intima-media thickness, thereby effectively realizing segmented estimation of the pulse wave velocity, and then obtaining the average pulse wave velocity of the entire segment; the automation of pulse wave velocity measurement is improved, and the influence of human intervention is reduced; segmentation is performed based on the intima-media thickness and its second-order derivative, so that the pulse wave velocity measurement is more accurate, and the average velocity directly calculated in the traditional method is effectively improved, while ignoring the fact that the pulse wave velocity actually changes at the position where the pulse wave has plaques, thereby making the pulse wave velocity measurement more accurate, which is helpful for early detection and evaluation of cardiovascular diseases such as atherosclerosis, or for staged evaluation of the progression or recovery of atherosclerosis.

[0006] A pulse wave velocity estimation method based on intima-media thickness, comprising:

[0007] Step 1: Acquire high frame rate images and identify the location of the blood vessel wall in the high frame rate images;

[0008] Step 2: Estimate the axial velocity of the vessel wall;

[0009] Step 3: When the axial velocity of the vessel wall is the largest, the intima-media thickness is identified based on the high frame rate image, and the vessel wall is segmented based on the intima-media thickness;

[0010] Step 4: Estimate the pulse wave velocity in segments and obtain the average pulse wave velocity of the entire segment.

[0011] Preferably, a pulse wave velocity estimation method based on intima-media thickness, in step 1, collecting high frame rate images, including:

[0012] Transmit full plane waves based on the long axis of the probe;

[0013] When receiving the reflected signal of the full plane wave, composite beamforming is performed on the echo IQ data, and equal to or greater than 1000 frames of vascular wall long-axis images are obtained according to the received apodization, wherein equal to or greater than 1000 frames of vascular wall long-axis images are high frame rate images.

[0014] Preferably, a pulse wave velocity estimation method based on intima-media thickness comprises:

[0015] The conditions for emitting full plane waves based on the long axis of the probe are: emitting at multiple emission angles, a frame rate equal to or greater than 1000 Hz, and a duration greater than 1 second;

[0016] At the same time, when the frame rate is equal to or greater than 1000 Hz and the duration is greater than 1 second, the formula for collecting image frames is as follows:

[0017] N=f 帧频 *T 持续时间 ;

[0018] Where N represents the number of image frames; f 帧频 Indicates the frame rate; T 持续时间 Indicates the total time of the collection.

[0019] Preferably, a pulse wave velocity estimation method based on intima-media thickness, in step 1, identifying the position of the blood vessel wall in the high frame rate image, comprises:

[0020] A sampling frame is set, and the blood vessel wall is automatically identified and scanned in the high-frequency frame image according to the sampling frame to obtain the maximum grayscale position of each column of the image;

[0021] The maximum grayscale position corresponding to each column of images is taken as a data point, and curve fitting is performed on the data points to obtain the shape of the blood vessel wall;

[0022] The position of the blood vessel wall in the high frame rate image is determined according to the shape of the blood vessel wall.

[0023] Preferably, a pulse wave velocity estimation method based on intima-media thickness, in step 2, estimating the axial velocity of the blood vessel wall comprises:

[0024] Extract the displacement between two adjacent frame signals in the high frame rate image, and analyze and calculate the displacement between two adjacent frame signals in the slow time direction to determine the axial velocity of the blood vessel wall;

[0025]

[0026] Among them, V 1D represents the estimated value of the axial velocity at the current position on the blood vessel wall; I represents the demodulated real signal at the current position on the blood vessel wall; Q represents the demodulated imaginary signal at the current position on the blood vessel wall; m represents the pixel point on the blood vessel wall; n represents the image frame; M represents the maximum coordinate in the fast direction; N represents the maximum number of frames in the slow direction; tan represents the tangent function;

[0027] The axial velocity is estimated for all frame images obtained within the duration T, and V 1D i,t , where i represents the abscissa of the blood vessel wall; t represents the time of the image frame;

[0028] According to the calculation results, when the axial velocity of the blood vessel wall is the maximum, it is determined that the pulse wave has passed.

[0029] Preferably, a pulse wave velocity estimation method based on intima-media thickness, in step 3, identifying the intima-media thickness according to the high frame rate image, comprises:

[0030] A two-dimensional function I(x, y) of the gray value in the sampling frame is obtained in the high-frequency frame image, where x and y are the horizontal and vertical coordinates of the image, respectively, and the gray value I(x, y) represents the intensity of the pixel at that position;

[0031] According to the following formula: Scan upward from the lower blood vessel wall to obtain the position value where the gray value in the lower blood vessel wall is the minimum;

[0032]

[0033] Among them, x i represents the horizontal coordinate value of the pixel point on the blood vessel wall; i represents the pixel point serial number value; y represents the vertical coordinate value of the pixel point on the blood vessel wall; i下血管壁 represents the ordinate value of the i-th pixel point of the lower blood vessel wall; Indicates the position value where the gray value of the lower blood vessel wall is the minimum; minI(x i ,y) represents the minimum gray value;

[0034] According to the position value when the gray value in the lower blood vessel wall is the minimum, the position of the lower intima-media membrane is determined;

[0035] According to the following formula: Scan downward along the upper blood vessel wall to obtain the position value when the gray value in the upper blood vessel wall is the minimum;

[0036]

[0037] in, Indicates the position value where the gray value is the minimum in the upper blood vessel wall; y i上血管壁 represents the ordinate value of the i-th pixel point on the upper blood vessel wall;

[0038] According to the position value when the gray value in the upper blood vessel wall is the minimum, the position of the upper intima-media membrane is determined;

[0039] The thickness of the intima-media membrane was determined based on the position of the inferior intima-media membrane and the position of the superior intima-media membrane.

[0040] Preferably, a pulse wave velocity estimation method based on the thickness of the intima-media membrane determines the thickness of the intima-media membrane according to the position of the lower intima-media membrane and the position of the upper intima-media membrane, comprising:

[0041] The thickness of the inferior intima-media membrane was calculated according to the following formula;

[0042] Among them, h 下 (x i ) represents the thickness of the inferior intima-media membrane;

[0043] The thickness of the superior intima-media membrane was calculated according to the following formula;

[0044] Among them, h 上 (x i ) represents the thickness of the superior intima-media membrane;

[0045] Calculate all x i The lower intima-media thickness and the upper intima-media thickness were calculated and the intima-media thickness curve was drawn to obtain the representation of the global intima-media thickness.

[0046] Preferably, a pulse wave velocity estimation method based on intima-media thickness, in step 3, segmenting the blood vessel wall according to the intima-media thickness, comprises:

[0047] Reading the drawn intima-media thickness curve, performing a second-order derivative operation on the intima-media thickness curve, and determining a maximum value and a minimum value of the second-order derivative of the intima-media thickness curve according to the calculation result;

[0048] Determine the segmentation start point and segmentation end point of the blood vessel wall according to the maximum and minimum values;

[0049] A segmentation boundary is determined based on a segmentation start point and a segmentation end point of the blood vessel wall, and the blood vessel wall is segmented according to the segmentation boundary.

[0050] Preferably, a pulse wave velocity estimation method based on intima-media thickness, in step 4, segmentally estimating the pulse wave velocity to obtain the average pulse wave velocity of the entire segment, comprises:

[0051] After completing the segmentation of the blood vessel wall, obtain the length L of each segment j At the same time, the propagation time Δt of the pulse wave in each segment is obtained j ;

[0052] According to the length L of each paragraph j The propagation time Δt of the pulse wave in each segment j Calculate the pulse wave velocity for each segment;

[0053] PWV j =L j / Δt j ;

[0054] Among them, PWV j represents the pulse wave velocity of the jth segment; L j represents the length of the jth paragraph; Δt j represents the propagation time of the pulse wave in the jth segment; j represents the sequence number of the segment;

[0055] The average pulse wave velocity of the entire segment is calculated according to the following formula;

[0056] PWV avg =∑L j / ∑Δt j ;

[0057] Among them, PWV avg Indicates the average pulse wave velocity of the entire segment.

[0058] A pulse wave velocity estimation system based on intima-media thickness, comprising:

[0059] An image acquisition module, used for acquiring high frame rate images and identifying the position of the blood vessel wall in the high frame rate images;

[0060] An axial velocity estimation module, used for estimating the axial velocity of the blood vessel wall;

[0061] A segmentation module, used for identifying the thickness of the intima-media membrane according to the high frame rate image when the axial velocity of the blood vessel wall is the largest, and segmenting the blood vessel wall according to the thickness of the intima-media membrane;

[0062] The pulse wave velocity estimation module is used to estimate the pulse wave velocity in segments and obtain the average pulse wave velocity of the entire segment.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] By acquiring high frame rate images, the position of the blood vessel wall can be effectively identified in the high frame rate images, and the degree of automation of pulse wave velocity measurement is improved. By estimating the axial velocity of the blood vessel wall, and when the axial velocity of the blood vessel wall is the largest, the thickness of the intima-media membrane is identified according to the high frame rate image, and the blood vessel wall is segmented according to the intima-media membrane thickness, the pulse wave velocity is effectively estimated in segments, and the average pulse wave velocity of the entire segment is obtained; the degree of automation of pulse wave velocity measurement is improved, and the influence of human intervention is reduced; segmentation is performed based on the intima-media membrane thickness and its second-order derivative, so that the pulse wave velocity measurement is more accurate, and the average velocity directly calculated in the traditional method is effectively improved, while ignoring the fact that the pulse wave velocity changes at the location of the plaque, so that the pulse wave velocity measurement is more accurate, which is helpful for the early detection and evaluation of cardiovascular diseases such as atherosclerosis, or for staged evaluation of the progression or recovery of atherosclerosis.

[0065] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures specifically pointed out in this application document.

[0066] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0068] Figure 1 This is a flow chart of a pulse wave velocity estimation method based on intima-media thickness in an embodiment of the present invention;

[0069] Figure 2 A gray value distribution diagram in a pulse wave velocity estimation method based on intima-media thickness according to an embodiment of the present invention;

[0070] Figure 3 is a curve showing the change of the maximum velocity of the blood vessel wall over time in a pulse wave velocity estimation method based on intima-media thickness in an embodiment of the present invention;

[0071] Figure 4 is a distribution diagram of the position of the intima-media membrane in a pulse wave velocity estimation method based on the thickness of the intima-media membrane in an embodiment of the present invention;

[0072] Figure 5 This is an example diagram of segmented estimation of pulse wave velocity in a pulse wave velocity estimation method based on intima-media thickness in an embodiment of the present invention;

[0073] Figure 6 4 is a structural diagram of a pulse wave velocity estimation system based on intima-media thickness in an embodiment of the present invention. DETAILED DESCRIPTION

[0074] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0075] Embodiment 1:

[0076] This embodiment provides a pulse wave velocity estimation method based on the thickness of the intima-media membrane. Figure 1 As shown, including:

[0077] Step 1: Acquire high frame rate images and identify the location of the blood vessel wall in the high frame rate images;

[0078] Step 2: Estimate the axial velocity of the vessel wall;

[0079] Step 3: When the axial velocity of the vessel wall is the largest, the intima-media thickness is identified based on the high frame rate image, and the vessel wall is segmented based on the intima-media thickness;

[0080] Step 4: Estimate the pulse wave velocity in segments and obtain the average pulse wave velocity of the entire segment.

[0081] In this embodiment, pulse wave velocity (PWV) is an important parameter for measuring arterial stiffness.

[0082] In this embodiment, the high frame rate image is equal to or greater than 1000 frames of the blood vessel wall long axis image.

[0083] In this embodiment, when the pulse wave passes through, the axial velocity of the blood vessel wall at this position is the largest.

[0084] In this embodiment, segmenting the blood vessel wall according to the intima-media thickness is based on the intima-media thickness and its second-order derivative, so that the pulse wave velocity measurement is more accurate.

[0085] The working principle and beneficial effects of the above technical solution are as follows: by acquiring high frame rate images, the position of the blood vessel wall can be effectively identified in the high frame rate images, thereby improving the automation of pulse wave velocity measurement; by estimating the axial velocity of the blood vessel wall, and when the axial velocity of the blood vessel wall is the largest, the thickness of the intima-media membrane is identified according to the high frame rate image, and the blood vessel wall is segmented according to the intima-media membrane thickness, thereby effectively realizing segmented estimation of the pulse wave velocity, and then obtaining the average pulse wave velocity of the entire segment; the automation of pulse wave velocity measurement is improved, and the influence of human intervention is reduced; segmentation is performed based on the intima-media membrane thickness and its second-order derivative, so that the pulse wave velocity measurement is more accurate, and the average velocity directly calculated in the traditional method is effectively improved, while ignoring the fact that the pulse wave velocity actually changes at the location where the pulse wave has plaques, thereby making the pulse wave velocity measurement more accurate, which is helpful for early detection and evaluation of cardiovascular diseases such as atherosclerosis, or for staged evaluation of the progression or recovery of atherosclerosis.

[0086] Embodiment 2:

[0087] Based on Example 1, this example provides a pulse wave velocity estimation method based on intima-media thickness. In step 1, a high frame rate image is acquired, including:

[0088] Transmit full plane waves based on the long axis of the probe;

[0089] When receiving the reflected signal of the full plane wave, composite beamforming is performed on the echo IQ data, and equal to or greater than 1000 frames of vascular wall long-axis images are obtained according to the received apodization, wherein equal to or greater than 1000 frames of vascular wall long-axis images are high frame rate images.

[0090] In this embodiment, the long axis of the probe is parallel to the blood vessel wall as much as possible, full plane wave transmission is adopted, multiple transmission angles are consistent, the frame rate is at least 1000 Hz, and the duration is more than 1 second. When receiving, the echo IQ data is composite beamformed, and in order to obtain a better image, receiving apodization can be adopted, and finally at least 1000 frames of blood vessel wall long axis images are obtained.

[0091] In this embodiment, the conditions for emitting full plane waves based on the long axis of the probe are: composite imaging at multiple emission angles, a frame rate equal to or greater than 1000 Hz, and a duration greater than 1 second;

[0092] At the same time, when the frame rate is equal to or greater than 1000 Hz and the duration is greater than 1 second, the formula for collecting image frames is as follows: N = f 帧频 *T 持续时间 ; Where N represents the number of image frames; f 帧频 Indicates the frame rate; T 持续时间 Indicates the total time of the collection.

[0093] The beneficial effect of the above technical solution is that better high-frequency frame images can be effectively obtained.

[0094] Embodiment 3:

[0095] Based on Example 1, this embodiment provides a pulse wave velocity estimation method based on intima-media thickness. In step 1, the position of the blood vessel wall is identified in the high frame rate image, including:

[0096] A sampling frame is set, and the blood vessel wall is automatically identified and scanned in the high-frequency frame image according to the sampling frame to obtain the maximum grayscale position of each column of the image;

[0097] The maximum grayscale position corresponding to each column of images is taken as a data point, and curve fitting is performed on the data points to obtain the shape of the blood vessel wall;

[0098] The position of the blood vessel wall in the high frame rate image is determined according to the shape of the blood vessel wall.

[0099] In this embodiment, the sampling frame setting should include the entire upper and lower walls of the blood vessel and less other tissues.

[0100] In this embodiment, the blood vessel wall is automatically identified and traced. In the process of blood vessel wall identification, the position y of the maximum gray value is obtained for each column of images. max (x i ), and polynomial fitting is performed on these points to obtain the shape of the blood vessel wall; this process includes the identification of the maximum gray value point and curve fitting, and the coefficients of the fitting curve are solved using the least squares method, such as Figure 2 shown.

[0101] Among them, maximum gray point identification: Assume that within the sampling frame of the image, the gray value distribution is a two-dimensional function I(x, y), where x and y are the horizontal and vertical coordinates of the image respectively, and the gray value I(x, y) represents the intensity of the pixel at that position; for each column x=x i (i.e. fixed x i ), there are two y 上max (x i ) and y 下max (x i ); from the top of the image down to I(x i ,y) value is 0 in this section, take the maximum gray value y 上max (x i ):y 上max (x i )=max I(x i ,y), for y>y I(x,y)＝0 ; Take the maximum gray value y from the bottom of the image to the section where I(x,y) value is 0 下max (x i):y 下max (x i )=max I(x i ,y), for y <y I(x,y)＝0 ;

[0102] Fitting of the maximum gray point: Set each column x=x i The corresponding two maximum grayscale positions y 上max (x i ) and y 下max (x i ) is considered as a data point (x i ,y 上max (x i )) and (x i ,y 下max (x i )), we can fit a curve to these points; if we use polynomial fitting, we can use a quadratic polynomial to fit these points. Fitting function y 上血管壁 (x) and y 下血管壁 (x) can be expressed as: y 上血管壁 (x) = a2x 2 +a1x+a0;y 下血管壁 (x) = a5x 2 +a4x+a3 where a5, a4, a3, a2, a1, a0 are the coefficients of the fitting curve. These coefficients can be determined by the Least Squares Method.

[0103] Embodiment 4:

[0104] Based on Example 1, this example provides a pulse wave velocity estimation method based on intima-media thickness. In step 2, estimating the axial velocity of the blood vessel wall includes:

[0105] Extract the displacement between two adjacent frame signals in the high frame rate image, and analyze and calculate the displacement between two adjacent frame signals in the slow time direction to determine the axial velocity of the blood vessel wall;

[0106]

[0107] Among them, V 1D represents the estimated value of the axial velocity at the current position on the blood vessel wall; I represents the demodulated real signal at the current position on the blood vessel wall; Q represents the demodulated imaginary signal at the current position on the blood vessel wall; m represents the pixel point on the blood vessel wall; n represents the image frame; M represents the maximum coordinate in the fast direction; N represents the maximum number of frames in the slow direction; tan represents the tangent function;

[0108] The axial velocity is estimated for all frame images obtained within the duration T, and V 1Di,t , where i represents the abscissa of the blood vessel wall; t represents the time of the image frame;

[0109] According to the calculation results, when the axial velocity of the blood vessel wall is the maximum, it is determined that the pulse wave has passed.

[0110] In this embodiment, when the pulse wave passes, the axial velocity of the blood vessel wall at this position is the largest, so a curve of the maximum velocity of the blood vessel wall changing with time can be obtained, such as Figure 3 shown.

[0111] The beneficial effect of the above technical solution is that the calculation of the axial velocity of the blood vessel wall can be effectively used as a measure of the pulse wave passing through, thereby effectively ensuring the effectiveness and timeliness of the pulse wave velocity estimation of the intima-media thickness.

[0112] Embodiment 5:

[0113] Based on Example 1, this example provides a pulse wave velocity estimation method based on the thickness of the intima-media membrane. In step 3, the thickness of the intima-media membrane is identified according to the high frame rate image, including:

[0114] A two-dimensional function I(x, y) of the gray value in the sampling frame is obtained in the high-frequency frame image, where x and y are the horizontal and vertical coordinates of the image, respectively, and the gray value I(x, y) represents the intensity of the pixel at that position;

[0115] According to the following formula: Scan upward from the lower blood vessel wall to obtain the position value where the gray value in the lower blood vessel wall is the minimum;

[0116] t 下minI(xi,y) =minI(x i ,y),y>y i下血管壁 ;

[0117] Among them, x i represents the horizontal coordinate value of the pixel point on the blood vessel wall; i represents the pixel point serial number value; y represents the vertical coordinate value of the pixel point on the blood vessel wall; i下血管壁 represents the ordinate value of the i-th pixel point on the lower blood vessel wall; t 下minI(xi,y) Indicates the position value where the gray value of the lower blood vessel wall is the minimum; minI(x i ,y) represents the minimum gray value;

[0118] According to the position value when the gray value in the lower blood vessel wall is the minimum, the position of the lower intima-media membrane is determined;

[0119] According to the following formula: Scan downward along the upper blood vessel wall to obtain the position value when the gray value in the upper blood vessel wall is the minimum;

[0120] t 上minI(xi,y) =minI(x i ,y),y <yi上血管壁 ;

[0121] Among them, t 上minI(xi,y) Indicates the position value where the gray value is the minimum in the upper blood vessel wall; y i上血管壁 represents the ordinate value of the i-th pixel point on the upper blood vessel wall;

[0122] According to the position value when the gray value in the upper blood vessel wall is the minimum, the position of the upper intima-media membrane is determined;

[0123] The thickness of the intima-media membrane was determined based on the position of the inferior intima-media membrane and the position of the superior intima-media membrane.

[0124] In this embodiment, along the lower blood vessel wall y i下血管壁 On the upward path (i.e. the direction of increasing y), we look for the gray value I(x i ,y) minimum position;

[0125] t 下minI(xi,y) =minI(x i ,y),y>y i下血管壁 ;

[0126] t 上minI(xi,y) =minI(x i ,y),y <y i上血管壁 ;

[0127] This formula means that at each x i Scan upward from the lower blood vessel wall to find the position with the smallest gray value, that is, the position of the lower intima-media membrane. Similarly, scan along the y line from the upper blood vessel wall. i下血管壁 The downward path (i.e. the direction of decreasing y) can also find an I(x i ,y) is the minimum position t 上minI(xi,y) , that is, the position of the upper intima-media membrane, as shown in Figure 4 shown.

[0128] In this embodiment, determining the thickness of the intima-media membrane according to the position of the lower intima-media membrane and the position of the upper intima-media membrane includes:

[0129] The thickness of the inferior intima-media membrane was calculated according to the following formula;

[0130] h 下 (x i ) = t 下minI(xi,y) -y i下血管壁 ; Among them, h 下 (x i ) represents the thickness of the inferior intima-media membrane;

[0131] The thickness of the superior intima-media membrane was calculated according to the following formula;

[0132] h 上 (x i ) = t上minI(xi,y) -y i上血管壁 ; Among them, h 上 (x i ) represents the thickness of the superior intima-media membrane;

[0133] Calculate all x i The lower intima-media thickness and the upper intima-media thickness were calculated and the intima-media thickness curve was drawn to obtain the representation of the global intima-media thickness.

[0134] As mentioned above, the thickness of the lower intima-media membrane h 下 (x i ) is defined as the i下血管壁 and the minimum gray value position t 下minI(xi,y) The vertical distance between

[0135] As mentioned above, the thickness of the upper intima-media membrane h 上 (x i ) is defined as the i上血管壁 and the minimum gray value position t 上minI(xi,y) The vertical distance between.

[0136] The working principle and beneficial effects of the above technical solution are as follows: Through the above formula description, the calculation process of the intima-media thickness can be clarified; first, the position of the lower vascular wall is determined, and then the distance from the lower vascular wall to the minimum grayscale value is found, which is the thickness of the intima-media h(x i ) ; by different positions x along the blood vessel i The calculation can obtain the complete distribution of the intima-media thickness, which helps to more accurately describe the thickness distribution of the intima-media of blood vessels and is beneficial for subsequent analysis and application.

[0137] Embodiment 6:

[0138] Based on Example 1, this example provides a pulse wave velocity estimation method based on intima-media thickness. In step 3, the blood vessel wall is segmented according to the intima-media thickness, including:

[0139] Reading the drawn intima-media thickness curve, performing a second-order derivative operation on the intima-media thickness curve, and determining a maximum value and a minimum value of the second-order derivative of the intima-media thickness curve according to the calculation result;

[0140] Determine the segmentation start point and segmentation end point of the blood vessel wall according to the maximum and minimum values;

[0141] A segmentation boundary is determined based on a segmentation start point and a segmentation end point of the blood vessel wall, and the blood vessel wall is segmented according to the segmentation boundary.

[0142] In this embodiment, in order to identify the thickness of the intima-media membrane, the identification process of the segmented boundary of the vascular wall can be described by the second-order derivative formula; assuming that the intima-media thickness curve is h(z), where z is the position along the length direction of the vascular wall, the second-order derivative h"(x) of the curve is expressed as: h"(x)=d 2 h(x) / dx 2 ; By finding the maximum and minimum values ​​of h"(x), the sharp part of the change in vascular wall thickness can be determined, thereby determining the starting and ending points of the segment. That is: x start = maxf0(h"(x)) and x end = minf0(h"(x))

[0143] The beneficial effect of the above technical solution is: segmentation based on the intima-media thickness and its second-order derivative makes the pulse wave velocity measurement more accurate, effectively improving the average velocity directly calculated in the traditional method, while ignoring the fact that the pulse wave velocity actually changes at the location where there is a plaque, thereby making the pulse wave velocity measurement more accurate.

[0144] Embodiment 7:

[0145] Based on Example 1, this example provides a pulse wave velocity estimation method based on the thickness of the intima-media membrane, such as Figure 5 As shown, in step 4, the pulse wave velocity is estimated in segments to obtain the average pulse wave velocity of the entire segment, including:

[0146] After completing the segmentation of the blood vessel wall, obtain the length L of each segment j At the same time, the propagation time Δt of the pulse wave in each segment is obtained j ;

[0147] According to the length L of each paragraph j The propagation time Δt of the pulse wave in each segment j Calculate the pulse wave velocity for each segment;

[0148] PWV j =L j / Δt j ;

[0149] Among them, PWV j represents the pulse wave velocity of the jth segment; L j represents the length of the jth paragraph; Δt j represents the propagation time of the pulse wave in the jth segment; j represents the sequence number of the segment;

[0150] The average pulse wave velocity of the entire segment is calculated according to the following formula;

[0151] PWV avg =∑L j / ∑Δt j ;

[0152] Among them, PWV avg Indicates the average pulse wave velocity of the entire segment.

[0153] The beneficial effect of the above technical solution is that the PWV (pulse wave velocity) estimation method based on automatic segmentation of the blood vessel wall based on the intima-media thickness and its second-order derivative can improve the automation and accuracy of PWV (pulse wave velocity) measurement, which is of great significance for the early diagnosis and risk assessment of cardiovascular diseases.

[0154] Embodiment 8:

[0155] A pulse wave velocity estimation system based on intima-media thickness, such as Figure 6 As shown, including:

[0156] An image acquisition module, used for acquiring high frame rate images and identifying the position of the blood vessel wall in the high frame rate images;

[0157] An axial velocity estimation module, used for estimating the axial velocity of the blood vessel wall;

[0158] A segmentation module, used for identifying the thickness of the intima-media membrane according to the high frame rate image when the axial velocity of the blood vessel wall is the largest, and segmenting the blood vessel wall according to the thickness of the intima-media membrane;

[0159] The pulse wave velocity estimation module is used to estimate the pulse wave velocity in segments and obtain the average pulse wave velocity of the entire segment.

[0160] The working principle and beneficial effects of the above technical solution are as follows: by acquiring high frame rate images, the position of the blood vessel wall can be effectively identified in the high frame rate images, thereby improving the automation of pulse wave velocity measurement; by estimating the axial velocity of the blood vessel wall, and when the axial velocity of the blood vessel wall is the largest, the thickness of the intima-media membrane is identified according to the high frame rate image, and the blood vessel wall is segmented according to the intima-media membrane thickness, thereby effectively realizing segmented estimation of the pulse wave velocity, and then obtaining the average pulse wave velocity of the entire segment; the automation of pulse wave velocity measurement is improved, and the influence of human intervention is reduced; segmentation is performed based on the intima-media membrane thickness and its second-order derivative, so that the pulse wave velocity measurement is more accurate, and the average velocity directly calculated in the traditional method is effectively improved, while ignoring the fact that the pulse wave velocity actually changes at the location where the pulse wave has plaques, thereby making the pulse wave velocity measurement more accurate, which is helpful for early detection and evaluation of cardiovascular diseases such as atherosclerosis, or for staged evaluation of the progression or recovery of atherosclerosis.

[0161] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A pulse wave velocity estimation method based on intima-media thickness, characterized in that: include: Step 1: Acquire high frame rate images and identify the location of the blood vessel wall in the high frame rate images; Step 2: Estimate the axial velocity of the vessel wall; Step 3: When the axial velocity of the vessel wall is the largest, the intima-media thickness is identified based on the high frame rate image, and the vessel wall is segmented based on the intima-media thickness; Step 4: Estimate the pulse wave velocity in segments and obtain the average pulse wave velocity of the entire segment.

2. The pulse wave velocity estimation method based on intima-media thickness according to claim 1, characterized in that: In step 1, high frame rate images are acquired, including: Transmit full plane waves based on the long axis of the probe; When receiving the reflected signal of the full plane wave, composite beamforming is performed on the echo IQ data, and equal to or greater than 1000 frames of vascular wall long-axis images are obtained according to the received apodization, wherein equal to or greater than 1000 frames of vascular wall long-axis images are high frame rate images.

3. The pulse wave velocity estimation method based on intima-media thickness according to claim 2, characterized in that: include: The conditions for emitting full plane waves based on the long axis of the probe are: emitting at multiple emission angles, a frame rate equal to or greater than 1000 Hz, and a duration greater than 1 second; At the same time, when the frame rate is equal to or greater than 1000 Hz and the duration is greater than 1 second, the formula for collecting image frames is as follows: N=f 帧频 *T 持续时间 ; Where N represents the number of image frames; f 帧频 Indicates the frame rate; T 持续时间 Indicates the total time of the collection.

4. The pulse wave velocity estimation method based on intima-media thickness according to claim 1, characterized in that: In step 1, the location of the blood vessel wall is identified in the high frame rate image, including: A sampling frame is set, and the blood vessel wall is automatically identified and scanned in the high-frequency frame image according to the sampling frame to obtain the maximum grayscale position of each column of the image; The maximum grayscale position corresponding to each column of images is taken as a data point, and curve fitting is performed on the data points to obtain the shape of the blood vessel wall; The position of the blood vessel wall in the high frame rate image is determined according to the shape of the blood vessel wall.

5. The pulse wave velocity estimation method based on intima-media thickness according to claim 1, characterized in that: In step 2, the axial velocity of the vessel wall is estimated, including: Extract the displacement between two adjacent frame signals in the high frame rate image, and analyze and calculate the displacement between two adjacent frame signals in the slow time direction to determine the axial velocity of the blood vessel wall; Among them, V 1D represents the estimated value of the axial velocity at the current position on the blood vessel wall; I represents the demodulated real signal at the current position on the blood vessel wall; Q represents the demodulated imaginary signal at the current position on the blood vessel wall; m represents the pixel point on the blood vessel wall; n represents the image frame; M represents the maximum coordinate in the fast direction; N represents the maximum number of frames in the slow direction; tan represents the tangent function; The axial velocity is estimated for all frame images obtained within the duration T, and V 1Di,t , where i represents the abscissa of the blood vessel wall; t represents the time of the image frame; According to the calculation results, when the axial velocity of the blood vessel wall is the maximum, it is determined that the pulse wave has passed.

6. The pulse wave velocity estimation method based on intima-media thickness according to claim 1, characterized in that: In step 3, the thickness of the intima-media membrane is identified based on the high frame rate image, including: A two-dimensional function I(x, y) of the gray value in the sampling frame is obtained in the high-frequency frame image, where x and y are the horizontal and vertical coordinates of the image, respectively, and the gray value I(x, y) represents the intensity of the pixel at that position; According to the following formula: Scan upward from the lower blood vessel wall to obtain the position value where the gray value in the lower blood vessel wall is the minimum; Among them, x i represents the horizontal coordinate value of the pixel point on the blood vessel wall; i represents the pixel point serial number value; y represents the vertical coordinate value of the pixel point on the blood vessel wall; i下血管壁 represents the ordinate value of the i-th pixel point of the lower blood vessel wall; Indicates the position value where the gray value of the lower blood vessel wall is the minimum; minI(x i ,y) represents the minimum gray value; According to the position value when the gray value in the lower blood vessel wall is the minimum, the position of the lower intima-media membrane is determined; According to the following formula: Scan downward along the upper blood vessel wall to obtain the position value when the gray value in the upper blood vessel wall is the minimum; in, Indicates the position value where the gray value is the minimum in the upper blood vessel wall; y i上血管壁 represents the ordinate value of the i-th pixel point on the upper blood vessel wall; According to the position value when the gray value in the upper blood vessel wall is the minimum, the position of the upper intima-media membrane is determined; The thickness of the intima-media membrane was determined based on the position of the inferior intima-media membrane and the position of the superior intima-media membrane.

7. The pulse wave velocity estimation method based on intima-media thickness according to claim 6, characterized in that: The thickness of the intima-media membrane is determined based on the position of the inferior intima-media membrane and the position of the superior intima-media membrane, including: The thickness of the inferior intima-media membrane was calculated according to the following formula; Among them, h 下 (x i ) represents the thickness of the inferior intima-media membrane; The thickness of the upper intima-media membrane was calculated according to the following formula; Among them, h 上 (x i ) represents the thickness of the superior intima-media membrane; Calculate all x i The lower intima-media thickness and the upper intima-media thickness were calculated and the intima-media thickness curve was drawn to obtain the representation of the global intima-media thickness.

8. The pulse wave velocity estimation method based on intima-media thickness according to claim 1, characterized in that: In step 3, the vessel wall is segmented according to the thickness of the intima-media membrane, including: Reading the drawn intima-media thickness curve, performing a second-order derivative operation on the intima-media thickness curve, and determining a maximum value and a minimum value of the second-order derivative of the intima-media thickness curve according to the calculation result; Determine the segmentation start point and segmentation end point of the blood vessel wall according to the maximum and minimum values; A segmentation boundary is determined based on a segmentation start point and a segmentation end point of the blood vessel wall, and the blood vessel wall is segmented according to the segmentation boundary.

9. The pulse wave velocity estimation method based on intima-media thickness according to claim 1, characterized in that: In step 4, the pulse wave velocity is estimated in segments to obtain the average pulse wave velocity of the entire segment, including: After completing the segmentation of the blood vessel wall, obtain the length L of each segment j At the same time, the propagation time Δt of the pulse wave in each segment is obtained j ; According to the length L of each paragraph j The propagation time Δt of the pulse wave in each segment j Calculate the pulse wave velocity for each segment; PWV j =L j / Δt j ; Among them, PWV j represents the pulse wave velocity of the jth segment; L j represents the length of the jth paragraph; Δt j represents the propagation time of the pulse wave in the jth segment; j represents the sequence number of the segment; The average pulse wave velocity of the entire segment is calculated according to the following formula; PWV avg =∑L j / ∑Δt j ; Among them, PWV avg Indicates the average pulse wave velocity of the entire segment.

10. A pulse wave velocity estimation system based on intima-media thickness, characterized in that: include: An image acquisition module, used for acquiring high frame rate images and identifying the position of the blood vessel wall in the high frame rate images; An axial velocity estimation module, used for estimating the axial velocity of the blood vessel wall; A segmentation module, used for identifying the thickness of the intima-media membrane according to the high frame rate image when the axial velocity of the blood vessel wall is the largest, and segmenting the blood vessel wall according to the thickness of the intima-media membrane; The pulse wave velocity estimation module is used to estimate the pulse wave velocity in segments and obtain the average pulse wave velocity of the entire segment.

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