KR102296166B1 - Estimation of Atherosclerotic Plaque using Two Dimensional Ultrasound Images Obtained From Human Carotid Artery - Google Patents

Abstract

The present invention relates to a method for estimating the shape and structure of atherosclerotic plaques from ultrasound images of arteries measured in two different directions, and more particularly, (A) an ultrasound image in the blood flow direction of the carotid artery with plaques ('length obtaining a cross-sectional direction ultrasound image (referred to as a 'cross-sectional image') of the position (P) where the hardened disc is thickest in the length image) and the length image; (B) the major axis is equal to the length of the hardened plate in the longitudinal image, the width at the position (P) is equal to the length of the hardened plate in the cross-sectional image, and the major axis and the minor axis intersect at a right angle at the position (P) creating a crosshair; and (C) a shaving step of deriving a projection plane consisting of a convex closed curve using a predetermined mathematical method from the location and distance information of the center of the crosshair and the four ends of the major and minor axes; It relates to an estimation method and a method for estimating the three-dimensional structure of a hardened disc using the same.

Description

Estimation of Atherosclerotic Plaque using Two Dimensional Ultrasound Images Obtained From Human Carotid Artery}

The present invention relates to a method for estimating the shape and structure of atherosclerotic plaques from ultrasound images of arteries measured in two different directions.

Atherosclerosis refers to the deposition of cholesterol on the innermost membrane (endothelium) of blood vessels and proliferation of endothelial cells in the blood vessels to form plaques, causing the blood vessels to narrow (stenosis) (see FIG. 1), and the blood vessels become peripheral. It is a disease that causes blood flow to the lungs. Atherosclerosis eventually leads to impaired blood circulation to the periphery, resulting in various symptoms. As of 2018, 11 million people in Korea are exposed to atherosclerosis (Non-Patent Document 1), and it is known to be an important cause of cardiovascular and cerebrovascular diseases, which rank second to third in mortality. Therefore, it is necessary to diagnose arteriosclerosis at an early stage and to periodically follow-up the disease progression of arteriosclerosis patients.

Atherosclerosis is being tested and diagnosed by several methods as follows.

The area and volume of arteriosclerosis occurring in the human brain blood vessels can be measured using a three-dimensional image by magnetic resonance imaging (MRI) or computed tomography (CT). However, according to this, not only expensive costs are required, but there is also a risk of adverse effects on the human body due to irradiation or use of contrast agents. And when it is necessary to follow up the progression of the disease, it becomes a burden due to high cost and radiation exposure.

Therefore, carotid artery ultrasonography, which does not use radiation, can obtain the tissue state of arteriosclerosis and blood flow velocity in real time, and is inexpensive, is widely used. According to this, it is possible to measure the area of the vascular stenosis, the blood flow rate due to the stenosis, and the length/area of the plaque. However, according to the conventional carotid ultrasound examination, the stenosis area measures the area on one side of the entire arteriosclerotic tissue, and the blood flow velocity measured at the most severe stenosis location differs for each individual/vessel as well as indirect information on arteriosclerosis, hardening. Since the length/area of the plaque is information about the long axis and cross-section, the overall outline and volume of arteriosclerosis (hardening plaque) cannot be known.

Ultrasonic flow-mediated dilation (FMD) using a phenomenon in which blood vessels are dilated by increasing shear force for local vascular endothelial cells that increase blood flow, and measurement of carotid intima-media thickness using ultrasound equipment (Carotid Intima-Media) Thickness, IMT) tests are also widely used. However, according to these, it is not possible to obtain information about the area, volume, or shape of the plaque because it is an indirect confirmation of the degree of arteriosclerosis (FMD) or measurement of the intima thickness at an arbitrary location (IMT). have.

Registered Patent 10-1059824 discloses that the intima start line, the relative media start line, and the adventitia start line of the blood vessel are separately read through the carotid artery ultrasound image, and the ratio of the intima thickness to the media thickness is calculated through each of the read lines. Measuring techniques are posted. However, according to this, information on the three-dimensional structure or volume of the hardened disk cannot be obtained.

JP 2010-88795 relates to an apparatus for extracting information on calcification of blood vessels, blood vessel lumen, outer walls of blood vessels, and blood vessel plaque from three-dimensional volume data of an image. According to this method, three-dimensional information of vascular plaque can be obtained, but a special device and 'three-dimensional volume data' are required.

Non-Patent Document 2 (Med Phys. 2002 Oct;29(10):2319-27.) attempts to quantify carotid plaque volume using a 3D ultrasound imaging device, but a 3D ultrasound imaging device that is expensive and complicated to use. is required

Registered Patent 10-1059824 JP 2010-88795

http://medicalinnovation.or.kr/%ED%8C%8C%EC%9D%B4%EB%82%B8%EC%85%9C%EB%89%B4%EC%8A%A4%ED%95 %9C%EA%B5%AD%EC%A7%80%EC%A7%88%C2%B7%EB%8F%99%EB%A7%A5%EA%B2%BD%ED%99%94%ED %95%99%ED%9A%8C-%EC%9D%B4%EC%83%81%EC%A7%80%EC%A7%88/ Med Phys. 2002 Oct;29(10):2319-27.

An object of the present invention is to provide a method for measuring the area, volume and shape of an atherosclerotic plaque simply and relatively accurately using a minimal two-dimensional ultrasound image of an artery.

Another object of the present invention is to provide a method for simply and relatively accurately measuring the area, volume, and shape of an atherosclerotic plaque using a generalized conventional ultrasound imaging apparatus.

Another object of the present invention is to minimize the physical and economic burden of a patient by providing an easy, inexpensive, safe and accurate arteriosclerosis examination method.

The present invention for achieving the above object

(A) Acquiring an ultrasound image in the blood flow direction of the carotid artery with plaque (referred to as a 'length image') and a cross-sectional ultrasound image (referred to as a 'section image') of the position (P) where the plaque is the thickest in the longitudinal image to do; (B) the major axis is equal to the length of the hardened plate in the longitudinal image, the width at the position (P) is equal to the length of the hardened plate in the cross-sectional image, and the major axis and the minor axis intersect at a right angle at the position (P) creating a crosshair; and (C) a shaving step of deriving a projection plane consisting of a convex closed curve using a predetermined mathematical method from the location and distance information of the center of the crosshair and the four ends of the major and minor axes; It is characterized in that it is an estimation method and a method for estimating the three-dimensional structure of a hardened disc using the same.

As described above, according to the present invention, it is possible to quickly measure the degree of arteriosclerosis, the range of stenosis, the size and structure of the plaque, and the like, by using widely available general ultrasound examination equipment.

In addition, according to the present invention, since arteriosclerosis can be inspected using a widely spread conventional ultrasound examination device, it is easy to diagnose arteriosclerosis quickly, at low cost and safely and to follow-up the patient over time.

1 is a conceptual diagram showing an example in which an atherosclerotic plaque is formed in a blood vessel.
Figure 2 is a blood vessel anatomical photograph showing the shape and thickness of the plaque according to the degree of progression.
3A is an example of one ultrasound length image and a cross-sectional image, respectively, obtained by the present invention.
3B is an exemplary view showing the results of the axial arrangement step and the shaving step of the estimation method according to the present invention;
Figure 3c is a view conceptually showing the change in the shape of the plaque according to the progression of arteriosclerosis.
4A is a view showing an example of a process for determining a cross section of a hardening plate in a long axis and a short axis in the method according to the present invention.
Figure 4b is a view showing the process of estimating the height of the hardening plate at any position in the method according to the present invention.
Figure 4c is a view showing a part of the process of measuring the height of the hardening disc at each position in the method according to the present invention.
Figure 5a is a conceptual diagram showing a three-dimensional structure of the hardening plate estimated by the method according to the present invention.
5B is a perspective view in which the three-dimensional structure of the hardening disc estimated according to the method according to the present invention is three-dimensionally combined with an ultrasound image.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. However, the accompanying drawings are only examples for easily explaining the content and scope of the technical idea of the present invention, and thereby the technical scope of the present invention is not limited or changed. It will be natural for those skilled in the art that various modifications and changes can be made within the scope of the technical spirit of the present invention based on these examples. In addition, if reference numerals are attached to the components of the claims, this is merely an example for description and is not intended to limit the components to the reference numerals.

As described above, the present invention relates to a method for estimating the surface shape and three-dimensional structure of an atherosclerotic plaque from a minimal ultrasound image, and is derived based on the following clinical and anatomical characteristics (see FIG. 2 ). ).

① Atherosclerotic plaques are formed long in the direction of blood flow.

② As arteriosclerosis progresses, the surface shape of the plaque changes from a thin oval to a rectangle with rounded corners, and the thickness of the plaque becomes thicker.

In FIG. 2 , it can be seen that the upper two cases have a thin oval shape and a relatively thin hardened plate, and the lower two cases have an approximately rectangular surface shape and a relatively thick hardened disc. [The size and shape of blood vessels and plaques are due to 'biological phenomena', so it is natural that they cannot have a mathematically standardized size and shape.]

(1) Method of estimating the surface shape of the hardened disk

The method for estimating the surface shape of a hardened disc according to the present invention comprises an image acquisition step , a shaft arrangement step, and a shaving step .

In the present invention, the image acquisition step is a minimal ultrasound image that is the basic data for estimating the surface shape of the plaque, that is, an ultrasound image in the blood flow direction of the carotid artery with the plaque (= stenosis) (referred to as a 'length image') and acquiring a cross-sectional direction ultrasound image (referred to as a 'cross-sectional image') of the position P where the hardened disc is thickest in the length image. 3A shows examples of one length image (left) and a cross-sectional image (right) respectively obtained in this way. It can be seen from the attached image that the vascular lining and the sclerosing duct are clearly distinguished, and this distinction can be made manually by an operator or automatically by a predetermined program or AI (referred to as 'program'). Hereinafter, it is assumed that this is done passively.

Subsequently, in the axial arrangement step , the long axis is the same as the hardened plate length in the longitudinal image, the width at the position (P) where the hardened disc is the thickest is the same as the hardened disc length in the cross-sectional image, and the position (P) Create a crosshair in which the major axis and the minor axis intersect at a right angle (see the left drawing in FIG. 3B ).

Referring to FIG. 3A, in the longitudinal and cross-sectional images, the beginning and end of the plaque (indicated by red dots), the thickest part of the plaque (indicated by light green dots), and the corresponding bottom surface (= inner wall of blood vessels) are positioned (indicated by a green dot) can be checked. Accordingly, the length of the major axis and the minor axis, and the position P at which the major axis and the minor axis intersect at a right angle are determined manually or automatically.

The side draw step in the present invention, for a predetermined manner for example from the position of the four ends of the center and the long and short axes of the cross-hair and the distance information, the method comprising utilizing a polynomial approximation to derive the four long home made of a convex closed curve ( See the right side view in FIG. 3B). There are various specific methods for deriving the projection plane, and two mathematical methods and one empirical method are exemplified below.

Mathematically, if four points are given, it can be expressed as a polynomial of the third degree. Therefore, a closed curve can be expressed as a cubic polynomial using the four ends (red dots) of the major and minor axes.

Another mathematical method is: Let L or L' be each straight line along the major axis at each endpoint of the minor axis. Let p' be the foot of the waterline that falls on the straight line L (or L') closest to p among the two straight lines at any point p on the boundary of the constructed hard disk. If the internal division of these two points is p'', the point p'' can be defined as in Equation 1 below.

p'' = a*p + (1-a)*p' (Equation 1)

If the point p'' is used as a new boundary of the hardened disc, various shapes of hardened discs can be obtained. Here, a may be determined in proportion to the thickness of the hardened plate. For example, the thickest part in the short-axis image may be set to 1, and a may be adjusted as a ratio of the thickness of the hardened plaque along the long axis. However, where a is greater than or equal to 0 and less than 1. [On the other hand, as above, the boundary of the hard disk made using p'' may not be a convex closed curve. To avoid this, a convex operation is performed. The embossing can be done using commercial or open software.]

Three examples of the shape of the hardened disc determined according to Equation 1 above based on the ultrasound image of FIG. 3A are shown. In each example, a is 0.1, 0.5 and 0.9.

On the other hand, as mentioned above with respect to the progression characteristics of the plaque, as arteriosclerosis progresses, the plaque transforms from a thin oval to a rectangle with rounded corners, and the thickness of the plaque increases. That is, there is a significant clinical anatomical relationship between the thickness of the plaque and the surface shape of the plaque. By reflecting these empirical facts in the shaving stage, it will be possible to 'empirically determine' the surface shape of the hardened plate. For example, depending on the degree of progression of arteriosclerosis, that is, the maximum thickness of the plaque is less than ~2 mm, 3-4 mm, and 6 mm or more, the closed curve shape may be sequentially changed as shown in FIG. 3C , respectively.

By the method of the present invention as described above, it is possible to estimate the surface shape of the intravascular plaque from two ultrasound images. Since the surface shape of the hardened disc is estimated, it is natural that the area of the hardened disc can be calculated based on this.

(2) Estimation method of three-dimensional structure of hardened disk

The present invention proposes a method for estimating the three-dimensional structure of an arteriosclerotic plaque including the image acquisition step , the shaft arrangement step , the shaving step , the shaft section determination step , the height determination step and the structure extraction step. Since the image acquisition step, the shaft arrangement step, and the shaving step are the same as described above, a re-description is omitted.

In the present invention, in the axial section determination step , in the projection plane derived through the shaving step, the height of the boundary is defined as 0, and the height and shape of the cross-section of the hardened plate in the length image and the cross-sectional image are defined as that of the projection plane. It is a step to reflect on the vertical section of the major axis and minor axis. Here, 'height' means the height of the plaque with reference to the inner wall of the blood vessel (0).

From FIG. 3A , an operator or a program may determine the height of the hardening plate along the major axis and the minor axis, that is, the shape and standard of the cross section of the hardening board in the major axis and the minor axis. 4A shows an example of a process for determining the cross-section of the hardened disk in the long axis and the short axis in the length image and the cross-sectional image.

In the longitudinal image of FIG. 4A , the orange line represents the inner vessel wall (= the reference plane of the long axis in the longitudinal direction), the green line represents the surface of the hard plaque on the long axis, and the lower light green curve in the cross-sectional image indicates the inner wall of the blood vessel (= the reference plane of the short axis in the cross-sectional direction). , and the green curve represents the uniaxial surface of the hardened plate. When the length image and the cross-sectional image are spread on a straight line, the shape and size of the hardened plate cross-section in the major axis and the minor axis are obtained.

Then, in the height determination step , the surface height of the hardened plate at any position (x, y) of the projection plane is calculated with reference to the boundary of the projection plane and the vertical cross-sections of the major and minor axes of the projection plane. That is, the height determination step is a process of estimating the height of an arbitrary position inside the projection plane. It will be described with reference to FIG. 4B.

Now, on the estimated surface shape of the hardening disk, a straight line passing through an arbitrary point inside the projection plane and at least one of the major axis or the minor axis always meets the interface twice. Hereinafter, for convenience of explanation, the straight line exemplifies two straight lines (blue and red lines, respectively) parallel to the major axis and the minor axis, respectively, as in FIG. 4B . At this time, since there are three points (p1, p2, p3) of known height on the plane perpendicular to the reference plane, including the blue line, a quadratic function passing through the three points can be obtained and the position of the point p is known. We can calculate the height u1 of the point p. In the same way, the height u2 of another point p with respect to the red line can be calculated. The operator or the program may determine either u1 or u2 as the height at the point p (= the thickness of the hardening plate), or may determine the height through an appropriate function using u1 and u2 as variables. When a function is used, the thickness can be determined by, for example, a partial differential equation as in Equation 2 below. In this case, a numerical analysis method according to the finite element method on the triangulated region may be selected (see FIG. 4c ).

(수식 2)

(Equation 2)

는 각 곡면에서 좌표 (x, y)인 p 위치의 높이에 관한 함수, [

is a function of the height of the position p, which is the coordinate (x, y) on each surface,

는 편도함수 기호,

is the partial derivative symbol,

f(x, y) is the sum of twice the coefficients of the highest order terms of the two quadratic functions]

Finally, in the structure derivation step , the three-dimensional structure of the hardened board is derived by reflecting both the thickness of the hardened board at arbitrary points of the projection plane in the above-described height determination step and the vertical section thickness information of the major axis and minor axis. In this case, the reference plane (the inner surface of the blood vessel) may be expressed as a flat surface, and the reference surface may be modified to have a round cross-sectional shape of the inner surface of the blood vessel by reflecting the reality. In FIG. 5A, a single three-dimensional structure of a hardened plaque with the same reference plane and the actual inner surface of the blood vessel is shown, and FIG. 5B is a perspective view in which it is three-dimensionally combined with the ultrasound image shown in FIG. 3A. Medical personnel will be able to properly utilize the stereoscopic view as shown in FIG. 5B to diagnose and explain to the patient the progress of arteriosclerosis of the patient.

Since the three-dimensional structure and specifications of the hardened disc are derived by the present invention, it is natural that the volume of the hardened disc can be calculated based on this and used for diagnosis and explanation.

The present invention includes a computer program in the form of a computer program stored in a computer readable recording medium or a computer readable recording medium in which the program is stored in order for a processor to perform the above-described method for estimating the surface shape of atherosclerotic plaque and estimating the three-dimensional structure.

Although the ultrasound image used in the description in the present invention is for the carotid artery, the method according to the present invention can be applied to all of the cerebrovascular, cardiovascular, or limb blood vessels as long as it is an artery that can obtain longitudinal and cross-sectional images of blood vessels as well as the carotid artery. will be.

In addition, in the above description of the present invention, one length image and one cross-sectional image were based, but this is with the minimization of cost in mind. It would be natural to be able to estimate the surface shape, area, three-dimensional structure and volume of the hardening plate more precisely and accurately by applying it.

Claims (9)

(A) Acquiring an ultrasound image in the blood flow direction of the carotid artery with plaque (referred to as a 'length image') and a cross-sectional ultrasound image (referred to as a 'section image') of the position (P) where the plaque is the thickest in the longitudinal image image acquisition step;
(B) the major axis is equal to the length of the hardened plate in the longitudinal image, the width at the position (P) is equal to the length of the hardened plate in the cross-sectional image, and the major axis and the minor axis intersect at a right angle at the position (P) Axial arrangement step of creating a crosshair;
(C) a shaving step of deriving a projection plane consisting of a convex closed curve using a predetermined mathematical method from the location and distance information of the center of the crosshair and the four ends of the major and minor axes;
Atherosclerotic plaque surface shape estimation method comprising a.
The method according to claim 1,
The projection plane is
A method for estimating the surface shape of an arteriosclerotic plaque, characterized in that it is adjusted from an oval to a rectangle in inverse proportion to the thickest thickness (height) of the plaque by a predetermined program.
A computer program stored in a computer-readable recording medium to enable a processor to perform the method for estimating the surface shape of an arteriosclerotic plaque according to claim 1 or 2.
A computer-readable recording medium in which the computer program according to claim 3 is stored.
(A) A blood flow direction ultrasound image (referred to as a 'length image') of the carotid artery in which the plaque was taken, and an ultrasound image in the cross-sectional direction (referred to as a 'cross-sectional image') of the position (P) where the plaque is the thickest in the longitudinal image. image acquisition step to acquire;
(B) the major axis is equal to the length of the hardened plate in the longitudinal image, the width at the position (P) is equal to the length of the hardened plate in the cross-sectional image, and the major axis and the minor axis intersect at a right angle at the position (P) Axial arrangement step of creating a crosshair;
(C) a shaving step of deriving a projection plane composed of a convex closed curve in a predetermined manner from the location and distance information of the center of the crosshair and the four ends of the major and minor axes by a predetermined program;
(D) defining the height of the projection plane boundary as 0, and reflecting the height and shape of the cross-section of the hardened plate in the longitudinal image and the cross-sectional image to the vertical sections of the major axis and the minor axis of the projection plane;
(E) a height determination step of calculating the height of the surface of the hardening plate at an arbitrary position (x, y) of the projection plane with reference to the boundary of the projection plane and the vertical section of the major axis and the minor axis of the projection plane; and
(F) a structure deriving step of deriving a three-dimensional structure of the hardening plate from the vertical section of the major axis and the minor axis of the projection plane and the surface height information at an arbitrary position on the projection plane;
A method for estimating the three-dimensional structure of atherosclerotic plaque, comprising:
6. The method of claim 5,
The projection plane is
A method for estimating the three-dimensional structure of an arteriosclerotic plaque, characterized in that it is adjusted from an oval to a rectangle in inverse proportion to the thickest thickness (height) of the plaque by a predetermined program.
6. The method of claim 5,
The height of the surface at any position (x. y) of the projection plane in the height determination step.
Calculated from the distance between the intersection (x, 0) of a line parallel to the major axis and the minor axis at an arbitrary position (x. y) and the intersection point of the boundary line (x, Y) and the surface height at the intersection of the minor axis (x, 0) a first height;
Calculated from the distance between the intersection of a line parallel to the minor axis (0, y) and the intersection of the boundary line (X, y) at an arbitrary location (x. y) and the surface height at the intersection of the minor axis (0, y) A three-dimensional structure estimation method of atherosclerotic plaque, characterized in that it is determined from the second height.
A computer program stored in a computer-readable recording medium so that the processor performs the method for estimating the three-dimensional structure of the hardening board according to any one of claims 5 to 7.
A computer-readable recording medium in which the computer program according to claim 8 is stored.

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