Calculation method of fractional flow reserve of main vascular trunks based on computational fluid dynamics

Abstract

The present disclosure describes a method for calculating the blood flow reserve fraction of a vascular trunk based on computational fluid dynamics, including: obtaining a medical image of the blood vessel, extracting the two-dimensional trunk parameters and two-dimensional branch parameters of the blood vessel; constructing a three-dimensional trunk model of the blood vessel, dividing the grid required for computational fluid dynamics calculations; dividing the two-dimensional trunk into multiple trunk segments based on the two-dimensional trunk parameters and two-dimensional branch parameters; calculating the relative pressure distribution of each trunk segment based on the calculated trunk flow and two-dimensional branch flow of each trunk segment and based on computational fluid dynamics and the grid; integrating the relative pressure distribution of each trunk segment to obtain the blood flow reserve fraction of the vascular trunk. According to the present disclosure, a method can be provided that only reconstructs the vascular trunk and uses CFD to perform numerical simulation on the reconstructed vascular trunk model to calculate the blood flow reserve fraction of the vascular trunk based on computational fluid dynamics.

Description

Technical Field

[0001] The present disclosure relates to the technical field of medical image data processing, and in particular to a method for calculating the blood flow reserve fraction of a main blood vessel based on computational fluid dynamics. Background Art

[0002] Conventional cardiovascular imaging techniques, such as coronary X-ray angiography, coronary CT angiography, and intravascular imaging, can image the coronary arteries and demonstrate the location and extent of vascular damage. However, they have limitations in determining whether damage has caused ischemia and locating the culprit vessel. Fractional Flow Reserve (FFR) can address these limitations, optimizing the diagnosis of ischemic heart disease and the selection of the culprit vessel, reducing unnecessary stent implantation and improving long-term treatment outcomes. It has become the gold standard for clinical evaluation of ischemic heart disease.

[0003] FFR can be calculated by dividing the maximum myocardial blood flow in the presence of epicardial coronary artery stenosis by the maximum blood flow in a normal vessel. Under conditions of maximum hyperemia, the blood flow ratio can be replaced by a pressure value. Therefore, using a pressure-sensitive coronary catheter, under conditions of maximum hyperemia, FFR can be calculated by comparing the pressure at the distal coronary stenosis (Pd) with the aortic pressure (Pa) obtained by the hemodynamic pressure sensor. Pressure-wire-guided FFR is an important hemodynamic indicator of coronary artery stenosis, but it has some limitations, such as the risk of invasive diagnosis causing harm to the patient, some patients reacting uncomfortably to adenosine infusion, and the high cost of pressure wires.

[0004] With the advancement of technology and research, particularly in medical imaging and reconstruction techniques and high-performance computing, the application of computational fluid dynamics (CFD) to calculate FFR is becoming a rapidly developing frontier. Compared to traditional FFR, CFD calculation is noninvasive. Clinical trials have shown that CFD-calculated FFR demonstrates exceptional accuracy, sensitivity, and specificity in diagnosing myocardial ischemia at the granular level of individual patients' vessels, surpassing imaging-based assessment methods.

[0005] Calculating FFR using CFD typically requires constructing a three-dimensional reconstruction of the offending vessel and its branches based on CT or coronary angiography images to obtain a geometric model of the offending vessel tree. During FFR calculation based on coronary angiography, the relative positions of the offending vessel branches and the offending vessel trunk are difficult to determine, making it difficult to construct a branched offending vessel tree. Even if a branched offending vessel tree is constructed, it is difficult to perform high-quality structured mesh segmentation on the complex vascular tree, which affects the calculation accuracy. Summary of the Invention

[0006] The present disclosure is proposed in view of the above-mentioned state of the prior art, and its purpose is to provide a method for reconstructing only the main vascular trunk and using CFD to perform numerical simulation on the reconstructed main vascular trunk model to calculate the blood flow reserve fraction of the main vascular trunk based on computational fluid dynamics.

[0007] The present disclosure provides a method for calculating the blood flow reserve fraction of a blood vessel trunk based on computational fluid dynamics, which comprises: acquiring a medical image of the blood vessel, extracting two-dimensional trunk parameters and two-dimensional branch parameters of the blood vessel according to the medical image; constructing a three-dimensional trunk model of the blood vessel based on the two-dimensional trunk parameters of multiple medical images, dividing the grid required for the computational fluid dynamics calculation based on the three-dimensional trunk model; dividing the two-dimensional trunk into multiple trunk segments based on the two-dimensional trunk parameters and the two-dimensional branch parameters; calculating the trunk reference diameters and two-dimensional branch reference diameters of the multiple trunk segments; making the contrast agent flow Through the main trunk of the blood vessel, and calculate the time for the contrast agent to flow through the main trunk of the blood vessel; based on the main reference diameters of multiple segments of the main trunk segments, the branch reference diameters of the two-dimensional branches, and the time for the contrast agent to flow through the main trunk of the blood vessel, calculate the main trunk flow of each segment of the main trunk and the branch flow of the two-dimensional branches; based on the calculated main trunk flow of each segment of the main trunk and the branch flow of the two-dimensional branches, and based on the computational fluid dynamics and the grid, calculate the relative pressure distribution of each segment of the main trunk; integrate the relative pressure distribution of each segment of the main trunk to obtain the blood flow reserve fraction of the main trunk of the blood vessel. In the present disclosure, on the one hand, based on the two-dimensional trunk parameters and two-dimensional branch parameters of the blood vessel, the two-dimensional trunk can be divided into multiple trunk segments. By calculating the trunk reference diameters of the multiple trunk segments and the branch reference diameters of the two-dimensional branches, as well as the time for the contrast agent to flow through the blood vessel trunk, the trunk flow of each trunk segment and the branch flow of the two-dimensional branches can be calculated; on the other hand, based on the two-dimensional trunk parameters of multiple medical images, a three-dimensional trunk model of the blood vessel can be constructed, and based on the three-dimensional trunk model, the grid required for computational fluid dynamics calculation can be divided; finally, according to the trunk flow of the trunk segment, based on computational fluid dynamics and the grid, the relative pressure distribution of each trunk segment can be calculated, and by integrating the relative pressure distribution of each trunk segment, the blood flow reserve fraction of the blood vessel trunk can be obtained. Compared with the general computational fluid dynamics method for calculating the blood flow reserve fraction, this method does not require the construction of a criminal blood vessel tree model, and has the advantages of conveniently designing a structured grid that conforms to the flow direction. It can calculate the blood flow reserve fraction more accurately and can perform an accurate functional evaluation of the blood vessel.

[0008] In addition, in the blood flow reserve fraction calculation method involved in the present disclosure, optionally, the two-dimensional trunk parameters may include a two-dimensional trunk centerline and a two-dimensional trunk contour line, and the two-dimensional branch parameters may include a two-dimensional branch contour line; based on the two-dimensional trunk centerline, a three-dimensional trunk centerline of the blood vessel can be constructed using spatial coordinate transformation; the three-dimensional trunk centerline of the blood vessel can be constructed based on the two-dimensional trunk centerlines of the blood vessel in the two medical images based on spatial coordinate transformation; and a three-dimensional trunk model of the blood vessel can be reconstructed based on the two-dimensional trunk contour line and the three-dimensional trunk centerline of the blood vessel. In this way, a three-dimensional trunk model of the blood vessel can be conveniently reconstructed, and the grid required for computational fluid dynamics calculations can be conveniently divided based on the three-dimensional trunk model.

[0009] In addition, in the blood flow reserve fraction calculation method of the present disclosure, the two-dimensional branch outline can optionally be extended toward the two-dimensional trunk, with the midpoint of the two intersections of the two-dimensional branch outline and the centerline of the two-dimensional trunk being the starting point of the two-dimensional branch; and the two-dimensional trunk can be divided into multiple trunk segments based on the starting points of the two-dimensional branches. This facilitates the construction of the starting points of the two-dimensional branches and allows the two-dimensional trunk to be divided into multiple trunk segments based on the starting points of the two-dimensional branches.

[0010] Additionally, in the Fractional Flow Reserve calculation method of the present disclosure, optionally, the trunk reference diameter is the maximum diameter of each trunk segment, and the branch reference diameter is the maximum diameter of the vascular branch closest to the trunk. This facilitates selection of the trunk reference diameter for each trunk segment and the branch reference diameter for each vascular branch.

[0011] In addition, in the method for calculating the fractional flow reserve involved in the present disclosure, optionally, the number of frames f1 of the angiographic image captured when the contrast agent appears at the entrance of the main blood vessel, and the number of frames f2 of the angiographic image captured when the contrast agent appears at the exit of the main blood vessel are recorded. The time interval between each two angiographic images is I. The expression for the time t during which the contrast agent flows through the main blood vessel is: t = (f2 - f1) × I. This facilitates calculation of the time t during which the contrast agent flows through the main blood vessel.

[0012] In addition, in the blood flow reserve fraction calculation method involved in the present disclosure, optionally, the blood vessel trunk may include a first trunk segment, a second trunk segment, ..., an Nth trunk segment, and a first two-dimensional branch, a second two-dimensional branch, ..., and an N-1th two-dimensional branch, the trunk reference diameter of the first trunk segment is d0, the flow rate flowing through the first trunk segment is Q0, the trunk reference diameter of the second trunk segment is d1, the flow rate flowing through the second trunk segment is Q1, and the branch reference diameter of the first two-dimensional branch is d1 *The flow rate flowing through the first two-dimensional branch is Q1 * , the branch reference diameter of the second two-dimensional branch is d2 * The flow rate flowing through the second two-dimensional branch is Q2 * , ..., the trunk reference diameter of the Nth trunk segment is d N-1 The flow rate flowing through the Nth trunk segment is Q N-1 The reference diameter of the N-1th two-dimensional branch is d N-1 * The flow rate flowing through the N-1th two-dimensional branch is Q N-1 * , according to Murray's law: d0 n =d1 n +(d1*) n =(d1*) n +(d2*) n +d2 n =(d1*) n +(d2*) n +(d3*) n +d3 n =(d1*) n +(d2*) n +(d3*) n +(d4*) n ……+(d N-1 *) n +d N-1 n , where n is the Murray coefficient, and the value of n ranges from 2 to 3, the flow distribution relationship is: Q1 = (d1 / d0) n ×Q0,Q1*=(d1* / d0) n ×Q0,Q2=(d2 / d1) n ×Q1,Q2*=(d2* / d1) n ×Q1,Q3=(d3 / d2) n ×Q2,Q3*=(d3* / d2) n ×Q2,……,Q N-1 =(d N-1 / d N-2 ) n ×Q N-2 , Q N-1 *=(d N-1 * / d N-2 ) n ×Q N-2 Thus, it is easy to construct the relationship between the trunk reference diameter and flow rate of each trunk segment, and the branch reference diameter and flow rate of each blood vessel branch.

[0013] In addition, in the blood flow reserve fraction calculation method involved in the present disclosure, optionally, the length of the first trunk segment is L0, the length of the second trunk segment is L1, ..., the length of the Nth trunk segment is L N-1 The time for the contrast agent to flow through the first trunk segment is t0, the time for the contrast agent to flow through the second trunk segment is t1, ..., the time for the contrast agent to flow through the Nth trunk segment is t N-1 , then: t0=L0×π×d0 2 / 8Q0,t1=L1×π×d1 2 / 8Q1,……,t N-1 =L N-1 ×π×d N-1 2 / 8Q N-1 , where π is the ratio of the circumference of a circle. Thus, the time it takes for the contrast agent to flow through each trunk segment can be easily constructed.

[0014] In addition, in the blood flow reserve fraction calculation method involved in the present disclosure, optionally, combined with the time t of the contrast agent flowing through the main blood vessel, t=t0+t1+...+t N-1 , set t0 = L0 × π × d0 2 / 8Q0,t1=L1×π×d1 2 / 8Q1,……,t N-1 =L N-1 ×π×d N-1 2 / 8Q N-1 Substitute into the flow Q0 of the first trunk segment, the flow Q1 of the second trunk segment, ..., the flow Q of the Nth trunk segment N-1 , and the flow rate Q1 of the first two-dimensional branch * , the flow rate Q2 of the second two-dimensional branch * , ..., the flow rate Q of the N-1th two-dimensional branch N-1 * Thus, the flow rate of each segment of the main blood vessel can be easily calculated.

[0015] In addition, in the method for calculating the fractional flow reserve involved in the present disclosure, optionally, based on the calculated trunk flow of each trunk segment, computational fluid dynamics simulation is performed on each trunk segment according to the grid. In each simulation, the relative pressure of each point on the three-dimensional trunk centerline of each trunk segment can be calculated, and a pressure drop curve for each trunk segment can be obtained. This facilitates the calculation of the relative pressure of each point on the three-dimensional trunk centerline of multiple trunk segments.

[0016] In addition, in the fractional flow reserve calculation method of the present disclosure, optionally, the relative pressure difference between two adjacent trunk segments on the three-dimensional trunk centerline is calculated, and based on the pressure difference, the pressure drop curve of each trunk segment is integrated into a pressure drop curve for the blood vessel trunk. This facilitates integrating the pressure drop curves of multiple trunk segments into a pressure drop curve for the entire blood vessel trunk.

[0017] According to the present disclosure, a method can be provided for reconstructing only the main vascular trunk and performing numerical simulation on the reconstructed main vascular trunk model using CFD to calculate the blood flow reserve fraction of the main vascular trunk based on computational fluid dynamics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present disclosure will now be explained in further detail, by way of example only, with reference to the accompanying drawings.

[0019] Figure 1 is a flow chart illustrating a method for calculating the blood flow reserve fraction involved in the present disclosure.

[0020] Figure 2 Schematic diagram showing the structure of a two-dimensional blood vessel involved in the present disclosure.

[0021] Figure 3 It is a structural schematic diagram showing the two-dimensional trunk center line and contour line and the two-dimensional branch contour line involved in the present disclosure.

[0022] Figure 4 It shows Figure 3 A magnified schematic diagram of area A in the middle.

[0023] Figure 5 is a schematic diagram showing the integrated multi-segment trunk segmentation involved in the present disclosure. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. In the following description, identical components are assigned identical reference numerals, and duplicate descriptions are omitted. In addition, the accompanying drawings are merely schematic, and the proportions of the dimensions of the components and the shapes of the components may differ from the actual ones.

[0025] It should be noted that the terms "including" and "having" and any variations thereof in this disclosure, such as a process, method, apparatus, product or equipment that includes or has a series of steps or units, are not necessarily limited to those steps or units clearly listed, but may include or have other steps or units that are not clearly listed or are inherent to these processes, methods, products or equipment.

[0026] In addition, the subheadings and the like in the following description of this disclosure are not intended to limit the content or scope of this disclosure, but are merely provided as a guide for reading. Such subheadings should not be understood as dividing the content of the article, nor should the content under the subheading be limited to the scope of the subheading.

[0027] The computational fluid dynamics-based method for calculating the fractional flow reserve of a main vascular trunk involved in this embodiment can be referred to as a method for calculating the fractional flow reserve of a main vascular trunk, or simply as a method for calculating the FFR (Fractional Flow Reserve) of a main vascular trunk, or simply as a calculation method. In the present disclosure, only the main vascular trunk can be reconstructed, and CFD (Computational Fluid Dynamics) can be used to perform numerical simulation on the reconstructed main vascular trunk model without considering the construction of vascular branches, thereby eliminating the need to construct a complete vascular tree model. As a result, the FFR of the main vascular trunk can be calculated more accurately, enabling a more accurate functional assessment of the coronary arteries.

[0028] Hereinafter, the FFR calculation method involved in this embodiment will be described in detail with reference to the accompanying drawings.

[0029] Figure 1 is a flow chart illustrating a method for calculating the blood flow reserve fraction involved in the present disclosure.

[0030] Reference Figure 1 In this embodiment, the method for calculating the blood flow reserve fraction of a main blood vessel based on computational fluid dynamics may include the following steps:

[0031] Step S100, obtaining a medical image of the blood vessel 10;

[0032] Step S200 , extracting two-dimensional trunk parameters of the blood vessel 10 and two-dimensional branch parameters of the blood vessel 10 from the medical image;

[0033] Step S300 , constructing a three-dimensional trunk model of the blood vessel 10 based on the two-dimensional trunk parameters of the blood vessel 10 ;

[0034] Step S400: The grid required for CFD calculation can be divided based on the three-dimensional backbone model;

[0035] Step S500 , dividing the two-dimensional trunk into multiple trunk segments based on the two-dimensional trunk parameters and the two-dimensional branch parameters;

[0036] Step S600, calculating the trunk reference diameter of the multiple trunk segments and the branch reference diameters of the two-dimensional branches;

[0037] Step S700, allowing the contrast agent to flow through the main blood vessel, and calculating the time it takes for the contrast agent to flow through the main blood vessel;

[0038] Step S800, calculating the trunk flow rate of each trunk segment and the branch flow rate of the two-dimensional branches based on the trunk reference diameters of the multiple trunk segments, the branch reference diameters of the two-dimensional branches, and the time for the contrast agent to flow through the blood vessel trunk;

[0039] Step S900: Based on the calculated trunk flow rate of each trunk segment and the branch flow rate of the two-dimensional branch, and based on computational fluid dynamics and the divided grid, the relative pressure distribution of each trunk segment can be calculated;

[0040] Step S1000 : integrating the relative pressure distribution of each trunk segment to obtain the blood flow reserve fraction of the vascular trunk.

[0041] In the present disclosure, on the one hand, a three-dimensional trunk model of the blood vessel 10 can be constructed based on the two-dimensional trunk parameters of the blood vessel 10 extracted from multiple medical images, and the grid required for computational fluid dynamics calculations can be divided based on the three-dimensional trunk model; on the other hand, the two-dimensional trunk can be divided into multiple trunk segments based on the two-dimensional trunk parameters and the two-dimensional branch parameters of the blood vessel 10. By calculating the trunk reference diameters of the multiple trunk segments and the branch reference diameters of the two-dimensional branches, as well as the time for the contrast agent to flow through the blood vessel trunk, the trunk flow of each trunk segment and the branch flow of the two-dimensional branches can be calculated; finally, based on the trunk flow of the trunk segment and the branch flow of the two-dimensional branches, the relative pressure distribution of each trunk segment can be calculated based on computational fluid dynamics and grids. By integrating the relative pressure distribution of each trunk segment, the blood flow reserve fraction of the blood vessel trunk can be obtained. Compared with the general CFD method for calculating FFR, this method does not require the construction of a criminal blood vessel tree model and has the advantages of conveniently designing a structured grid that conforms to the flow direction. It can more accurately calculate FFR and perform accurate functional evaluation of the blood vessel.

[0042] It is understandable that Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows and are executed sequentially in the order of the step numbers. However, unless otherwise specified herein, there is no strict order restriction for the execution of these steps. In some other examples, these steps may also be executed in other orders. For example, in some examples, there is no strict order requirement for the execution of steps S400 and S500; they may be executed sequentially or simultaneously. In some examples, there is no strict order requirement for the execution of step S700; it may be executed simultaneously with step S600 or before step S100.

[0043] In some examples, in step S100 , a medical image related to the heart may be acquired.

[0044] In some examples, in step S200 , a three-dimensional trunk model of the coronary arteries may be constructed based on medical images of the heart.

[0045] In some examples, the heart-related medical image may be a two-dimensional image, a three-dimensional image, or another form of image capable of characterizing coronary artery lesions, such as an X-ray angiography image, a CT angiography image, an MRI angiography image, etc. In this embodiment, preferably, a two-dimensional medical image may be used, and the medical image described in this disclosure may be a coronary artery angiography image.

[0046] Figure 2 Schematic diagram showing the structure of a two-dimensional blood vessel involved in the present disclosure. Figure 3 It is a structural schematic diagram showing the two-dimensional trunk center line and contour line and the two-dimensional branch contour line involved in the present disclosure. Figure 4 It shows Figure 3 A magnified schematic diagram of area A in the middle.

[0047] Reference Figure 2 In some examples, blood vessel 10 ( Figure 2 The two-dimensional blood vessel 10 may generally include a two-dimensional blood vessel trunk 110 and two-dimensional blood vessel branches 120 (or referred to as the two-dimensional trunk 110 and the two-dimensional branches 120). In the present disclosure, a distinction may be made between the two-dimensional blood vessel trunk 110 and the blood vessel trunk, with the blood vessel trunk being used to represent a physical blood vessel trunk or a three-dimensional blood vessel trunk.

[0048] In some examples, reference Figure 2 The blood vessel 10 may have a two-dimensional trunk 110 and a plurality of two-dimensional branches 120. In some examples, the two-dimensional branches 120 may include a first two-dimensional branch 121, a second two-dimensional branch 122, and a third two-dimensional branch 123.

[0049] Reference Figure 3 In some examples, the two-dimensional trunk parameters may include a two-dimensional trunk centerline 101 and a two-dimensional trunk contour line 102 . In some examples, the two-dimensional branch parameters may include a two-dimensional branch contour line 103 .

[0050] In some examples, a three-dimensional main centerline of the blood vessel 10 can be constructed using a spatial coordinate transformation based on the two-dimensional main centerline 101. In some examples, a three-dimensional main centerline of the blood vessel 10 can be constructed using a spatial coordinate transformation based on the two-dimensional main centerline 101 of the blood vessel 10 in two medical images. In some examples, a three-dimensional main model of the blood vessel 10 can be reconstructed using a spatial coordinate transformation based on the two-dimensional main contour line 102 of the blood vessel 10 and the three-dimensional main centerline of the blood vessel 10. This facilitates the reconstruction of a three-dimensional main model of the blood vessel 10. Furthermore, the three-dimensional main model can be used to easily partition the grid required for computational fluid dynamics calculations.

[0051] Reference Figure 4 In some examples, the two-dimensional branch contour line 103 can be extended toward the two-dimensional trunk 110 (i.e., the two-dimensional branch contour lines 103a and 103b are extended respectively). The midpoint C of the two intersections of the two-dimensional branch contour lines 103a and 103b with the two-dimensional trunk centerline 101 can serve as the starting point of the two-dimensional branch 120. In some examples, the two-dimensional trunk can be divided into multiple trunk segments based on the starting point C of the two-dimensional branch 120. In this way, the starting point C of the two-dimensional branch 120 can be easily constructed, and the two-dimensional trunk can be divided into multiple trunk segments based on the starting point C of the two-dimensional branch 120.

[0052] Combine Figures 2 to 4 In some examples, based on multiple branches on the two-dimensional trunk 110 (e.g., the first two-dimensional branch 121, the second two-dimensional branch 122, and the third two-dimensional branch 123), the above method can be used to divide the two-dimensional trunk 110 into a first two-dimensional trunk segment 111, a second two-dimensional trunk segment 112, a third two-dimensional trunk segment 113, and a fourth two-dimensional trunk segment 114. In other words, based on the N branches on the two-dimensional trunk 110, the two-dimensional trunk 110 can be divided into N+1 two-dimensional trunk segments (or simply trunk segments).

[0053] In some examples, the trunk reference diameter may be the maximum diameter of each trunk segment. In some examples, because the diameter of the blood vessel trunk tends to decrease gradually along the direction of blood flow, the diameter at the starting position of each trunk segment may be used as the trunk reference diameter.

[0054] In some examples, the branch reference diameter can be the maximum diameter of a vascular branch (or two-dimensional branch 120) at its closest point to the vascular trunk. In other words, the branch reference diameter can be the diameter of the vascular branch at its starting point when it extends from the two-dimensional trunk 110. This facilitates the selection of a trunk reference diameter for each trunk segment and a branch reference diameter for each vascular branch.

[0055] In some examples, the trunk reference diameter and the branch reference diameter can be directly measured when executing steps S200 and S500. That is, during the process of extracting the two-dimensional trunk parameters and the two-dimensional branch parameters from the medical image and dividing the two-dimensional trunk 110 into multiple trunk segments, the numerical measurements of the two-dimensional trunk parameters and the two-dimensional branch parameters can be performed directly on the image or picture.

[0056] In some examples, a contrast agent may be allowed to flow through a main blood vessel and the flow of the contrast agent may be captured. The number of frames f1 of the contrast image captured when the contrast agent appears at the entrance of the main blood vessel and the number of frames f2 of the contrast image captured when the contrast agent appears at the exit of the main blood vessel may be recorded. The time interval between each two contrast images is 1. The expression for the time t during which the contrast agent flows through the main blood vessel is:

[0057] t=(f2-f1)×I……Formula (1)

[0058] Thus, the time t for the contrast agent to flow through the main blood vessel can be easily calculated. For example, the imaging can be started in advance before the contrast agent enters the blood vessel or the target blood vessel to be measured. When the contrast agent appears at the entrance of the main blood vessel, the number of frames of the angiographic image captured is 4 (i.e., the 4th frame is captured). When the contrast agent appears at the exit of the main blood vessel, the number of frames of the angiographic image captured is 14 (i.e., the 14th frame is captured). Assuming that the time interval between each two angiographic images is 0.1 s, the time t for the contrast agent to flow through the main blood vessel is: t = (14-4) * 0.1 = 1 s.

[0059] In some examples, the two-dimensional blood vessel trunk 110 may include a first trunk segment 111 , a second trunk segment 112 , . . . , an Nth trunk segment, and a first two-dimensional branch 121 , a second two-dimensional branch 122 , . . . , and an N−1th two-dimensional branch.

[0060] The trunk reference diameter of the first trunk segment 111 is d0, and the flow rate flowing through the first trunk segment 111 is Q0 (the flow rate Q0 can be the flow rate flowing into the entrance of the two-dimensional blood vessel trunk 110), the trunk reference diameter of the second trunk segment 112 is d1, and the flow rate flowing through the second trunk segment 112 is Q1, and the branch reference diameter of the first two-dimensional branch is d1 * The flow rate flowing through the first two-dimensional branch is Q1 * , the branch reference diameter of the second two-dimensional branch is d2 * The flow rate flowing through the second two-dimensional branch is Q2 * , ..., the trunk reference diameter of the Nth trunk segment is d N-1 The traffic flowing through the Nth trunk segment is Q N-1 , the branch reference diameter of the N-1th two-dimensional branch is d N-1 *The flow rate flowing through the N-1th two-dimensional branch is Q N-1 * .

[0061] According to Murray's law:

[0062] d0 n =d1 n +(d1*) n =(d1*) n +(d2*) n +d2 n =(d1*) n +(d2*) n +(d3*) n +d3 n =(d1*) n +(d2*) n +(d3*) n +(d4*) n ……+(d N-1 *) n +d N-1 n ...Formula (2)

[0063] Where n is the Murray coefficient, and the value of n can range from 2 to 3.

[0064] The traffic distribution relationship is:

[0065] Q1=(d1 / d0) n ×Q0,...Formula (3-1)

[0066] Q1*=(d1* / d0) n ×Q0,...Formula (3-1')

[0067] Q2=(d2 / d1) n ×Q1,...Formula (3-2)

[0068] Q2*=(d2* / d1) n ×Q1,...Formula (3-2')

[0069] Q3=(d3 / d2) n ×Q2,...Formula (3-3)

[0070] Q3*=(d3* / d2) n ×Q2,...Formula (3-3')

[0071] ...,

[0072] Q N-1 =(d N-1 / d N-2 ) n×Q N-2 ,...Formula (3-N-1)

[0073] Q N-1 *=(d N-1 * / d N-2 ) n ×Q N-2 ...Formula (3-N-1')

[0074] In this way, it is possible to conveniently construct a relationship between the trunk reference diameter and flow rate of each trunk segment, and the branch reference diameter and flow rate of each blood vessel branch.

[0075] In some examples, the flow rate referred to above may be the flow rate flowing into the entrance of the corresponding trunk segment or blood vessel branch.

[0076] In some examples, the length of the first trunk segment is L0, the length of the second trunk segment is L1, ..., the length of the Nth trunk segment is L N-1 The time it takes for the contrast agent to flow through the first trunk segment is t0, the time it takes for the contrast agent to flow through the second trunk segment is t1, ..., the time it takes for the contrast agent to flow through the Nth trunk segment is t N-1 According to the above relationship, we have:

[0077] t0=L0×π×d0 2 / 8Q0, ...Formula (4-0)

[0078] t1=L1×π×d1 2 / 8Q1,...Formula (4-1)

[0079] ...,

[0080] t N-1 =L N-1 ×π×d N-1 2 / 8Q N-1 ,...Formula (4-n)

[0081] Here, π is the ratio of the circumference of a circle to the circumference of a circle. This makes it easy to construct an expression for the time it takes for the contrast agent to flow through each trunk segment.

[0082] In this embodiment, the length of the vascular trunk may be the length of the three-dimensional trunk centerline, and the length of the vascular trunk segment may be the length of the three-dimensional trunk centerline of the segment.

[0083] Specifically, taking the first trunk segment as an example, the flow rate Q0 flowing through the first trunk segment is:

[0084] Q0=π×(d0 / 2) 2 ×v,...Formula (5)

[0085] Where v represents the average flow velocity of the contrast agent in the blood vessels.

[0086] And 2v=L0 / t0, ...Formula (6)

[0087] Among them, 2v represents the maximum flow velocity of the contrast agent in the blood vessel, that is, the velocity of the contrast agent flowing in the center of the blood vessel.

[0088] Combining the above formulas (5) and (6), we can derive formula (4-0), which is t0 = L0 × π × d0. 2 / 8Q0.

[0089] In some examples, a line integral can be performed on each trunk segment in three-dimensional space to determine the length of each trunk segment. In this case, since blood vessels are three-dimensional vessels, i.e., they torsionally extend in three dimensions, the length of each trunk segment can be accurately determined by considering the position of the blood vessels in three dimensions.

[0090] In some examples, combined with the time t for the contrast agent to flow through the main blood vessel, we have:

[0091] t=t0+t1+……+t N-1 ...Formula (7)

[0092] Convert formula (4-0) to formula (4-n) (i.e., t0 = L0 × π × d0 2 / 8Q0,t1=L1×π×d1 2 / 8Q1,……,t N-1 =L N-1 ×π×d N-1 2 / 8Q N-1 ) into formula (7), and combined with formula (3-1) to formula (3-N-1'), we can obtain the flow rate Q0 of the first trunk segment, the flow rate Q1 of the second trunk segment, ..., the flow rate Q of the Nth trunk segment N-1 , and the flow rate Q1 of the first two-dimensional branch * The flow of the second two-dimensional branch is Q2 * , ..., the flow rate Q of the N-1th two-dimensional branch N-1 * Thus, the flow rate of each segment of the main blood vessel can be easily calculated.

[0093] Figure 5 is a schematic diagram showing the integrated multi-segment trunk segmentation involved in the present disclosure.

[0094] Reference Figure 5In some examples, based on the calculated trunk flow of each trunk segment, computational fluid dynamics simulation is performed on each trunk segment based on a grid. In each simulation, the relative pressure of each point on the three-dimensional trunk centerline of each trunk segment can be calculated, and the pressure drop curve of each trunk segment can be obtained based on the relative pressure of each point on the three-dimensional trunk centerline of each trunk segment.

[0095] In some examples, a first simulation is used as an example, and the first simulation uses flow rate Q0 as the inlet boundary condition of the first trunk segment 111 (or blood vessel trunk). In some examples, the relative pressure at the starting point of the first trunk segment 111 can be set to 0. Assuming that the three-dimensional trunk centerline of the first trunk segment 111 is composed of multiple equally spaced points, combined with the pressure characteristics of blood flowing in the blood vessel (pressure gradually decreases along the flow direction), the relative pressure of each point can be calculated through CFD simulation, thereby constructing a pressure drop curve L111 for the first trunk segment 111.

[0096] The second simulation uses the flow rate Q1 as the inlet boundary condition of the second trunk segment 112, combines the pressure characteristics of blood flowing in the blood vessels, and uses CFD simulation to calculate the relative pressure of each point on the three-dimensional trunk centerline of the second trunk segment 112.

[0097] In some examples, during the second simulation, a random value can be set for the relative pressure at the starting point of the second trunk segment 112. When calculating the relative pressure at each point on the 3D centerline of the second trunk segment 112, the relative pressure at the starting point of the second trunk segment 112 can be compared with the relative pressure at the end point of the first trunk segment 111 to obtain a relative pressure difference. The relative pressure at the starting point of the second trunk segment 112 can also be taken as the relative pressure at the end point of the 3D centerline of the first trunk segment 111. This relative pressure difference can then be subtracted from the relative pressure at each subsequent point on the 3D centerline of the second trunk segment 112 to obtain a new set of relative pressure values ​​for each point on the 3D centerline of the second trunk segment 112. Based on this new set of relative pressure values ​​for each point on the 3D centerline of the second trunk segment 112, a pressure drop curve L112 for the second trunk segment 112 can be constructed.

[0098] Similarly, the pressure drop curve L113 of the third trunk segment 113, ..., and the pressure drop curve of the Nth trunk segment 113 can be obtained. In this case, the relative pressure and pressure drop curve of each trunk segment can be independently calculated, thereby improving calculation efficiency.

[0099] By combining or integrating the pressure drop curve L111 of the first trunk segment 111, the pressure drop curve L112 of the second trunk segment 112, the pressure drop curve L113 of the third trunk segment 113, and so on, and finally the pressure drop curve of the Nth trunk segment 113, a pressure drop curve for the entire blood vessel trunk can be obtained. In this case, the relative pressures along the three-dimensional trunk centerline of the adjacent trunk segments at both ends can be connected end to end, thereby conveniently constructing a pressure drop curve for the entire blood vessel trunk.

[0100] In some examples, after the first simulation of the first trunk segment 111 is completed, the relative pressure at the end point of the 3D trunk centerline of the first trunk segment 111 can be directly used as the relative pressure value at the start point of the 3D trunk centerline of the second trunk segment 112. Furthermore, the relative pressure at each point on the 3D trunk centerline of the second trunk segment 112 can be calculated through CFD simulation, thereby constructing a pressure drop curve for the second trunk segment 112.

[0101] In some examples, the above steps can be used to calculate a pressure drop curve for the entire vessel trunk, where the relative pressure at the starting point of the 3D centerline of the vessel trunk (the entrance to the vessel trunk) is zero. At this point, the true pressure drop curve for the entire vessel trunk is obtained by adding the relative pressure at each point on the pressure drop curve to the aortic pressure (Pa). Finally, the pressure at each point on the true pressure drop curve is divided by the aortic pressure (Pa) to obtain the FFR curve.

[0102] According to the present disclosure, a method can be provided for reconstructing only the main vascular trunk and performing numerical simulation on the reconstructed main vascular trunk model using CFD to calculate the blood flow reserve fraction of the main vascular trunk based on computational fluid dynamics.

[0103] Although the present disclosure has been described in detail above with reference to the accompanying drawings and examples, it will be understood that the above description does not limit the present disclosure in any form. Those skilled in the art may modify and change the present disclosure as needed without departing from the spirit and scope of the present disclosure, and such modifications and variations all fall within the scope of the present disclosure.

Claims

1. A method for calculating the blood flow reserve fraction of a main vascular trunk based on computational fluid dynamics, characterized in that: include: Acquiring a medical image of the blood vessel, and extracting two-dimensional trunk parameters and two-dimensional branch parameters of the blood vessel based on the medical image; constructing a three-dimensional trunk model of the blood vessel based on the two-dimensional trunk parameters of the plurality of medical images, and dividing the grid required for the computational fluid dynamics calculation based on the three-dimensional trunk model; Dividing the two-dimensional trunk into a plurality of trunk segments based on the two-dimensional trunk parameters and the two-dimensional branch parameters; Calculating a trunk reference diameter and a branch reference diameter of a plurality of trunk segments; allowing a contrast agent to flow through the main blood vessel, and calculating the time it takes for the contrast agent to flow through the main blood vessel; Calculating the trunk flow rate of each of the trunk segments and the branch flow rate of the two-dimensional branches based on the trunk reference diameters of the plurality of trunk segments, the branch reference diameters of the two-dimensional branches, and the time for the contrast agent to flow through the blood vessel trunk; Calculating the relative pressure distribution of each trunk segment according to the calculated trunk flow of each trunk segment and the branch flow of the two-dimensional branch, based on the computational fluid dynamics and the grid; The relative pressure distribution of each trunk segment is integrated to obtain the blood flow reserve fraction of the blood vessel trunk.

2. The method for calculating blood flow reserve fraction according to claim 1, wherein: The two-dimensional trunk parameters include a two-dimensional trunk centerline and a two-dimensional trunk contour line, and the two-dimensional branch parameters include a two-dimensional branch contour line; The three-dimensional main centerline of the blood vessel is constructed using spatial coordinate transformation based on the two-dimensional main centerline of the blood vessel in the two medical images, and the three-dimensional main model of the blood vessel is reconstructed based on the two-dimensional main contour line of the blood vessel and the three-dimensional main centerline of the blood vessel.

3. The method for calculating blood flow reserve fraction according to claim 2, wherein: Extending the two-dimensional branch outline in the direction of the two-dimensional trunk, the midpoint of the two intersections of the two-dimensional branch outline and the center line of the two-dimensional trunk is the starting point of the two-dimensional branch; The two-dimensional trunk is divided into a plurality of trunk segments based on the starting points of the two-dimensional branches.

4. The method for calculating blood flow reserve fraction according to claim 3, wherein: The trunk reference diameter is the maximum diameter of each trunk segment, and the branch reference diameter is the maximum diameter of the blood vessel branch closest to the blood vessel trunk.

5. The method for calculating blood flow reserve fraction according to claim 3, wherein: Record the frame number f1 of the angiography image taken when the contrast agent appears at the entrance of the main blood vessel, and the frame number f2 of the angiography image taken when the contrast agent appears at the exit of the main blood vessel. The time interval between each two angiography images is I. The expression of the time t that the contrast agent flows through the main blood vessel is: t = (f2-f1)×I.

6. The method for calculating blood flow reserve fraction according to claim 5, characterized in that: The blood vessel trunk includes a first trunk segment, a second trunk segment, ..., an Nth trunk segment, and a first two-dimensional branch, a second two-dimensional branch, ..., and an N-1th two-dimensional branch. The trunk reference diameter of the first trunk segment is d0, the flow rate flowing into the first trunk segment is Q0, the trunk reference diameter of the second trunk segment is d1, the flow rate flowing into the second trunk segment is Q1, and the branch reference diameter of the first two-dimensional branch is d1. * The flow rate flowing into the first two-dimensional branch is Q1 * , the branch reference diameter of the second two-dimensional branch is d2 * The flow rate flowing into the second two-dimensional branch is Q2 * , ..., the trunk reference diameter of the Nth trunk segment is d N-1 The flow rate flowing into the Nth trunk segment is Q N-1 The reference diameter of the N-1th two-dimensional branch is d N-1 * The flow rate flowing into the N-1th two-dimensional branch is Q N-1 * , According to Murray's law, d0 n =d1 n +(d1*) n =d1 n +(d2*) n +d2 n =d1 n +(d2*) n +(d3*) n +d3 n =d1 n +(d2*) n +(d3*) n +(d4*) n ……+(d N-1 *) n +d N-1 n , where n is the Murray coefficient, and the value of n ranges from 2 to 3. The flow distribution relationship is: Q1 = (d1 / d0) n ×Q0,Q1*=(d1* / d0) n ×Q0,Q2=(d2 / d1) n ×Q1,Q2*=(d2* / d1) n ×Q1,Q3=(d3 / d2) n ×Q2,Q3*=(d3* / d2) n ×Q2,……,Q N-1 =(d N-1 / d N-2 ) n ×Q N-2 , Q N-1 *=(d N-1 * / d N-2 ) n ×Q N-2 .

7. The method for calculating blood flow reserve fraction according to claim 6, characterized in that: The length of the first trunk segment is L0, the length of the second trunk segment is L1, ..., the length of the Nth trunk segment is L N-1 The time for the contrast agent to flow through the first trunk segment is t0, the time for the contrast agent to flow through the second trunk segment is t1, ..., the time for the contrast agent to flow through the Nth trunk segment is t N-1 , then: t0=L0×π×d0 2 / 8Q0,t1=L1×π×d1 2 / 8Q1,……,t N-1 =L N-1 ×π×d N-1 2 / 8Q N-1 , where π is the ratio of the circumference of a circle to its circumference.

8. The method for calculating blood flow reserve fraction according to claim 7, characterized in that: Combined with the time t of the contrast agent flowing through the main blood vessel, we have t=t0+t1+...+t n , set t0 = L0 × π × d0 2 / 8Q0,t1=L1×π×d1 2 / 8Q1,……,t N-1 =L N-1 ×π×d N-1 2 / 8Q N-1 Substitute into the flow Q0 of the first trunk segment, the flow Q1 of the second trunk segment, ..., the flow Q of the Nth trunk segment N-1 , and the flow rate Q1 of the first two-dimensional branch * , the flow rate Q2 of the second two-dimensional branch * , ..., the flow of the N-1th two-dimensional branch is Q N-1 * The value of .

9. The method for calculating blood flow reserve fraction according to claim 8, characterized in that: Based on the calculated trunk flow of each trunk segment, computational fluid dynamics simulation is performed on each trunk segment according to the grid, and the relative pressure of each point on the three-dimensional trunk centerline of each trunk segment is calculated in each simulation to obtain a pressure drop curve for each trunk segment.

10. The method for calculating blood flow reserve fraction according to claim 9, characterized in that: The pressure difference between the relative pressures on the three-dimensional trunk centerline of two adjacent trunk segments is calculated, and the pressure drop curve of each trunk segment is integrated into the pressure drop curve of the blood vessel trunk according to the pressure difference.

Images