Calculation method and system of coronary microvascular resistance and FFR

Abstract

The present invention relates to a method for calculating microvascular resistance at the end of coronary arteries and a method and system for calculating FFR. The method for calculating microvascular resistance at the end of coronary arteries includes the following steps: firstly, a coronary tree model is established based on medical images to determine the volume of the myocardium, multiple collateral vessels are added to the coronary tree model, the size of the blood supply myocardium of each coronary outlet is determined according to the radius of each coronary outlet, and then a microcirculation vessel model is established by continuously performing cross operations, and the microcirculation resistance value of each coronary outlet is calculated based on the microcirculation vessel model and blood routine data using Poiseuille's theorem and Farin effect. Compared with the prior art, the present invention adds collateral vessels to the coronary tree model, and the obtained coronary tree model is more in line with the actual physiological situation. Then, by establishing the microcirculation vessel model, the microcirculation resistance value of the coronary outlet is accurately obtained, and the boundary conditions in the FFR calculation are set according to the microcirculation resistance value, thereby improving the accuracy of the FFR calculation.

Description

Technical Field

[0001] The present invention relates to the field of human physiology and hemodynamics, and in particular to a method and system for calculating coronary terminal microvascular resistance and FFR. Background Art

[0002] The main cause of coronary heart disease is coronary artery stenosis caused by arteriosclerosis. The fractional flow reserve (FFR) refers to the ratio of the maximum blood flow that can be obtained by the myocardial area supplied by the blood vessel to the maximum blood flow that can be obtained by the same area under normal conditions in theory when there is a stenotic lesion in the coronary artery. It can be simplified as the ratio of the mean pressure in the coronary artery distal to the stenosis (Pd) under the state of maximum myocardial hyperemia to the mean pressure in the aorta at the coronary artery orifice (Pa). FFR can indicate the impact of coronary artery stenosis on distal blood flow and is used to assess whether the myocardium is ischemic. FFR has become a recognized indicator for the functional evaluation of coronary artery stenosis.

[0003] When determining FFR, it is necessary to calculate FFR based on the blood flow velocity under the maximum congestion state of the myocardium and the mean pressure of the aorta at the coronary artery orifice, and to obtain the mean pressure in the coronary artery distal to the stenosis through different means. At present, most methods of obtaining FFR are invasive, with high risks and high costs. In order to solve the above problems, researchers have proposed a non-invasive measurement method of FFR that combines coronary CTA and computational fluid dynamics (CFD), such as a system for using computational fluid dynamics (CFD) to simulate and calculate the blood flow reserve fraction and a method for setting corresponding inlet boundary conditions and outlet boundary conditions for the computational fluid dynamics CFD model of the vascular tree disclosed in Chinese patent CN201611234903.1.

[0004] Coronary CTA can accurately assess the degree of coronary stenosis and identify the nature of wall plaques. It is a non-invasive and easy-to-operate method for diagnosing coronary artery lesions. Assuming that blood is an incompressible Newtonian fluid, blood flow can be calculated using the Navier-Stokes equation, the basic governing equation of fluid mechanics. A vascular tree model is constructed based on CTA images, and the inlet, outlet and boundary conditions are defined. Then, a coronary hemodynamic model is constructed based on the Navier-Stokes equation, and physiological parameters such as cardiac output, aortic pressure and microcirculatory resistance are simulated and introduced to calculate FFR.

[0005] CTA images are combined with computational fluid dynamics (CFD) for numerical modeling. The calculated CTFFR combines the advantages of coronary CTA and FFR, and can evaluate coronary artery stenosis from both structural and functional aspects, becoming a new non-invasive detection system that provides anatomical and functional information of coronary artery lesions. However, since the microcirculatory resistance at the end of the coronary artery is difficult to accurately give according to the patient's characteristics during the numerical modeling process, there is a certain difference between the CTFFR obtained by numerical simulation and the actual measured FFR, which greatly limits the clinical use of CTFFR. Summary of the invention

[0006] The purpose of the present invention is to provide a method and system for calculating the microvascular resistance at the end of the coronary artery and the calculation method and system of FFR in order to overcome the defects of the above-mentioned prior art. After the coronary tree model is established according to the medical image, the side branch vessels are added to the coronary tree model, and the obtained coronary tree model is more in line with the actual physiological situation. Then, the microcirculation vascular model is established by continuously performing bifurcation operations, so as to accurately obtain the microcirculation resistance value of the coronary artery outlet, and then the boundary conditions in the FFR calculation are set according to the microcirculation resistance value, thereby improving the accuracy of the FFR calculation.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for calculating coronary terminal microvascular resistance comprises the following steps:

[0009] S1: acquiring routine blood data and medical images of the heart, performing segmentation and reconstruction processing on the medical images, and obtaining a coronary tree model, wherein the coronary tree model includes the aorta root, and determining the volume of the myocardium and the radius of each coronary outlet based on the coronary tree model;

[0010] S2: Add multiple side branches to the coronary tree model, that is, add multiple coronary artery outlets;

[0011] S3: for the N coronary artery outlets on the coronary artery tree model, based on the volume of the myocardium and the radius of each coronary artery outlet, the volume of the myocardium supplied by each coronary artery outlet is determined respectively;

[0012] S4: Generate a microcirculatory vascular model based on the radius of the coronary artery outlet and the volume of the myocardium supplied by the coronary artery outlet. The specific process is as follows:

[0013] S41: Initialize and generate a microcirculatory vascular model, wherein the microcirculatory vascular model includes N coronary artery outlets, and each coronary artery outlet is used as a parent generation, and step S42 is executed;

[0014] S42: each parent generation performs a bifurcation operation, and one parent generation obtains multiple children, each of which is a blood vessel. The blood supply myocardium of the parent generation is allocated to each child generation, and all children generations are added to the microcirculation blood vessel model according to the corresponding relationship between the children and the parent generation;

[0015] S43: Traverse all the children obtained in the previous step, if there is a radius greater than r 0 The descendants of all the 0 The child of is taken as the parent, and step S42 is executed; otherwise, the generation of the small blood vessel tree model is completed;

[0016] Among them, r 0 The minimum vessel radius of the pre-set microcirculation vascular model;

[0017] S5: Based on the microcirculatory vascular model and routine blood data, the microcirculatory resistance value of each coronary artery outlet is calculated using Poiseuille's theorem and Fallin effect.

[0018] Preferably, in step S2, p (1≤p≤7) side branch vessels are added to the coronary artery tree model, and the side branch vessels are added at a side of the coronary artery close to the heart and between the upper and lower bifurcations of the existing coronary artery. The length of the side branch vessel is 3-5 mm, and the radius of the side branch vessel is the minimum radius value of the existing blood vessels on the coronary artery tree model.

[0019] Preferably, the medical image of the heart in step S1 is a cardiac CT image, and step S1 specifically comprises: acquiring a cardiac CT image, segmenting the cardiac CT image, obtaining a myocardial image through morphological operations and grayscale extraction, and determining the volume of the myocardium; segmenting the cardiac CT image, obtaining a coronary tree including the aortic root through morphological operations and grayscale extraction, determining the area of ​​each coronary outlet, and using the equivalent radius of each coronary outlet as the radius of each coronary outlet; calculating and reconstructing the centerline and vascular wall of each blood vessel, and establishing a coronary tree model.

[0020] Preferably, the value of p is determined by the change in the blood vessel area between the upper and lower bifurcations. Assuming that the following relationship exists between the blood vessel radius before and after the coronary artery bifurcation: the nth power of the blood vessel radius before the bifurcation = the sum of the nth power of the coronary artery radius after the bifurcation, the value of p satisfies the following formula:

[0021] p*(r 侧枝血管 ) n =(r 上级分叉 ) n -(r 下级分叉 ) n

[0022] Among them, r 侧枝血管 represents the radius of the collateral vessel, r 上级分叉represents the radius of the vessel downstream of the superior bifurcation, r 下级分叉 It represents the radius of the upstream blood vessel of the lower bifurcation, and the value range of n is 2.3-2.44.

[0023] Preferably, in step S3, the calculation formula for the volume of the myocardium supplied by the i-th (1≤i≤N) coronary artery outlet is as follows:

[0024]

[0025] Among them, V i represents the volume of the myocardium supplied by the i-th coronary artery outlet, V represents the volume of the myocardium, r i represents the radius of the i-th coronary artery outlet, r k represents the radius of the kth coronary artery outlet, and the value of n ranges from 2.3 to 2.44.

[0026] Preferably, in step S42, a parent generation performs a fork operation as follows:

[0027] The blood supply myocardium of the parent generation is equivalent to an ellipsoid, and a point on the surface of the ellipsoid is taken as the root node. The root node represents the location of the parent generation's exit. The ellipsoid is evenly divided into m (2≤m≤5) sub-parts through the root node. The center of mass of each sub-part is found respectively, and the center of mass is connected with the root node. The m line segments obtained are m offspring. The volume of the blood supply myocardium of each offspring is the volume of one sub-part. The radius of the m offspring is the same, and the radius of the offspring is r 子代 The radius r of the parent 父代 Satisfies the relationship: m*(r 子代 ) n =(r 父代 ) n .

[0028] Preferably, when performing the bifurcation operation, the blood supplying myocardium of the parent generation is equivalent to a sphere.

[0029] Preferably, when performing the bifurcation operation, the ellipsoid is equally divided into two sub-parts through the root node.

[0030] Preferably, in step S43, the preset minimum blood vessel radius r of the microcirculation blood vessel model 0 The size is 0.005mm.

[0031] Preferably, in step S5, the resistance value of each blood vessel segment is calculated using Poiseuille's theorem, wherein the viscosity coefficient is obtained using the Faring effect, the hematocrit in the Faring effect is determined by routine blood data, and the microcirculation resistance value of each coronary artery outlet is calculated using the series-parallel theorem of resistance.

[0032] A method for calculating FFR, which calculates the microvascular resistance based on the method for calculating the microvascular resistance of the coronary artery end as described above to set boundary conditions, includes the following steps:

[0033] A1: Obtain a medical image of the heart, perform segmentation and reconstruction processing on the medical image to obtain a coronary artery tree model, add p collateral vessels to the coronary artery tree model, and determine the volume of the myocardium and the radius of each coronary artery outlet;

[0034] A2: Based on the volume of the myocardium and the radius of each coronary artery outlet, determine the volume of the myocardium supplied by each coronary artery outlet, generate a microcirculation blood vessel model, and calculate the microcirculation resistance values of each coronary artery outlet;

[0035] A3: Generate a computational fluid dynamics calculation grid, establish a three-dimensional CFD model of the coronary artery tree model and a one-dimensional CFD model of the microcirculation blood vessel model, and obtain the physical properties of the blood and the flow equation;

[0036] A4: Set the boundary conditions of the three-dimensional CFD model. The boundary conditions include an inlet boundary condition and an outlet boundary condition. Setting the boundary conditions includes the following steps:

[0037] A41: Set each inlet boundary condition of the three-dimensional CFD model to the blood pressure P of the corresponding coronary artery orifice 0 , and set each outlet boundary condition of the three-dimensional CFD model to a times (0 < a < 1) of the blood pressure of the corresponding coronary artery orifice, that is, the pressure P at each outlet of the three-dimensional CFD model = a * P 0 ;

[0038] A42: Obtain the current boundary conditions of the three-dimensional CFD model. For each outlet of the three-dimensional CFD model, solve the three-dimensional CFD model based on the physical properties of the blood and the flow equation to obtain the blood flow Q at each outlet of the three-dimensional CFD model;

[0039] A43: The inlets of the one-dimensional CFD model correspond one by one to the outlets of the three-dimensional CFD model. Set each inlet boundary condition of the one-dimensional CFD model to the blood flow Q at the corresponding outlet of the three-dimensional CFD model, and set each outlet boundary condition of the one-dimensional CFD model to the venous pressure Pout;

[0040] A44: Calculate the blood pressure Pin at each inlet of the one-dimensional CFD model according to the formula Pin - Pout = R * Q. If Pin is not equal to P and the difference is greater than the preset convergence accuracy, then correct each outlet boundary condition of the three-dimensional CFD model respectively. The correction formula is P` = (P * 4 + Pin) / 5, and repeat step A42. Otherwise, use the current boundary conditions of the three-dimensional CFD model as the finally set boundary conditions;

[0041] Among them, R represents the microcirculation resistance value, and P` represents the outlet boundary condition of the modified three-dimensional CFD model;

[0042] A5: Based on the boundary conditions of the three-dimensional CFD model, the physical properties of blood and the flow equation, the fluid parameters at each position of the coronary tree model are solved, and the blood flow reserve fraction FFR is calculated based on the solved fluid parameters.

[0043] Preferably, the fluid parameters include flow rate, pressure and velocity.

[0044] Preferably, the value of a is 0.7.

[0045] A FFR calculation system, comprising:

[0046] A coronary tree model generation module is used to obtain a medical image of the heart, segment and reconstruct the medical image, obtain a coronary tree model, and add p side branches to the coronary tree model;

[0047] Microcirculatory vascular module, used to establish a microcirculatory vascular model and calculate the microcirculatory resistance value corresponding to each coronary artery outlet on the coronary tree model;

[0048] A computational grid generation module, used to generate computational fluid dynamics computational grids for the coronary tree model and the microcirculation blood vessel model, thereby establishing a three-dimensional CFD model of the coronary tree model and a one-dimensional CFD model of the microcirculation blood vessel model;

[0049] Boundary condition setting module, used to set the boundary conditions of the three-dimensional CFD model;

[0050] Property setting module, used to set the physical properties and flow equations of blood;

[0051] A solver, based on the boundary conditions of the three-dimensional CFD model, the physical properties of blood and the flow equation, solves the three-dimensional CFD model to obtain the fluid parameters at various locations of the coronary tree model;

[0052] The post-processing module performs post-processing based on the fluid parameters at various locations in the coronary tree model to obtain the blood flow reserve fraction FFR.

[0053] Preferably, in the property setting module, based on routine blood data and the Fallin effect formula, it is assumed that the blood is a Newtonian fluid or a generalized Newtonian fluid, and laminar flow, individual-specific blood density and blood viscosity are adopted; the flow equation includes a steady flow equation or an unsteady flow equation, and a Navier-Stokes equation group based on incompressible flow.

[0054] Preferably, in the post-processing module, multiple sections are cut on the coronary tree model, and the mean arterial pressure on each section is obtained, which is then divided by the mean arterial pressure at the coronary artery orifice to obtain the blood flow reserve fraction of each section, wherein the mean pulsating pressure of a section is the mean pulsating pressure of the section within a cardiac cycle.

[0055] Preferably, the selected position of the cross section includes between the upper and lower bifurcations of the coronary artery.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) After establishing the coronary artery tree model based on medical images, collateral vessels are added to the coronary artery tree model, so that the obtained coronary artery tree model is more in line with the actual physiological situation. Then, the microcirculation vascular model is established by continuously performing bifurcation operations, so as to accurately obtain the microcirculation resistance value of the coronary artery outlet.

[0058] (2) In the calculation process of the blood flow reserve fraction, the boundary exit conditions that are more in line with the actual physiological conditions are set according to the obtained microcirculatory resistance values, thereby reducing the difference between the coronary artery tree model and the actual physiological conditions of the human body, thereby improving the accuracy of the blood flow reserve fraction calculation.

[0059] (3) When adding collateral vessels, it is assumed that the nth power of the vessel radius before the bifurcation is equal to the sum of the nth power of the coronary artery radius after the bifurcation. The minimum radius of the vessel on the current coronary tree model is used as the radius of the collateral vessel, and then the number of collateral vessels is determined. This eliminates the error caused by the generation of the coronary tree model from medical images to a certain extent, and the final coronary tree model is more in line with the actual physiological condition of the human body.

[0060] (4) When generating the microcirculatory vascular model, the blood supply myocardium is equivalent to a sphere, and then a bifurcation operation is performed. The parent generation is subjected to the bifurcation operation to obtain two offspring generations, and then the blood supply myocardium of the parent generation is evenly divided into the two offspring generations until the radius of the offspring is less than 0.005 mm, which is more in line with the physiological conditions of the human body and has a higher accuracy of microcirculatory resistance.

[0061] (5) The calculation of FFR in this application does not require the support of invasive medical data, which reduces medical costs and avoids the risks of invasive testing. At the same time, the coronary artery tree model constructed in this application can accurately predict the effect of coronary treatment, which is helpful for the planning of clinical treatment plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 The flowchart is a method for calculating the terminal coronary microvascular resistance;

[0063] Figure 2 It is a schematic diagram of the architecture of the FFR calculation system;

[0064] Figure 3 Flowchart for generating microcirculatory vascular models. DETAILED DESCRIPTION

[0065] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0066] Embodiment 1:

[0067] A method for calculating the end-coronary microvascular resistance, such as Figure 1 As shown, the following steps are included:

[0068] S1: Obtain routine blood data and medical images of the heart, segment and reconstruct the medical images, and obtain a coronary tree model. The coronary tree model contains the aortic root, and the volume of the myocardium and the radius of each coronary outlet are determined based on the coronary tree model;

[0069] In this embodiment, the medical image of the heart is a cardiac CT image, and step S1 specifically comprises: acquiring a cardiac CT image, segmenting the cardiac CT image, obtaining a myocardial image through morphological operations and grayscale extraction, and determining the volume of the myocardium; segmenting the cardiac CT image, obtaining a coronary tree including the aortic root through morphological operations and grayscale extraction, determining the area of ​​each coronary outlet, and using the equivalent radius of each coronary outlet as the radius of each coronary outlet; calculating and reconstructing the centerline and vascular wall of each blood vessel, and establishing a coronary tree model.

[0070] S2: Add multiple side branches to the coronary tree model, that is, add multiple coronary artery outlets;

[0071] In this embodiment, p (1≤p≤7) side branch vessels are added to the coronary artery tree model. The side branch vessels are added at the side of the coronary artery close to the heart and between the upper and lower bifurcations of the existing coronary artery. The length of the side branch vessels is 3-5 mm, and the radius of the side branch vessels is the minimum radius value of the existing blood vessels on the coronary artery tree model.

[0072] The value of p is determined by the change in the blood vessel area between the upper and lower bifurcations. Assuming that the following relationship exists between the blood vessel radius before and after the coronary artery bifurcation: the nth power of the blood vessel radius before the bifurcation = the sum of the nth power of the coronary artery radius after the bifurcation, the value of p satisfies the following formula:

[0073] p*(r 侧枝血管 ) n =(r 上级分叉 ) n -(r 下级分叉 ) n

[0074] Among them, r 侧枝血管 represents the radius of the collateral vessel, r 上级分叉 represents the radius of the vessel downstream of the superior bifurcation, r 下级分叉 It represents the radius of the upstream blood vessel of the lower bifurcation, and the value range of n is 2.3-2.44.

[0075] S3: for the N coronary artery outlets on the coronary artery tree model, based on the volume of the myocardium and the radius of each coronary artery outlet, the volume of the myocardium supplied by each coronary artery outlet is determined respectively;

[0076] Specifically, the calculation formula for the volume of the myocardium supplied by the i-th (1≤i≤N) coronary artery outlet is as follows:

[0077]

[0078] Among them, V i represents the volume of the myocardium supplied by the i-th coronary artery outlet, V represents the volume of the myocardium, r i represents the radius of the i-th coronary artery outlet, r k represents the radius of the kth coronary artery outlet, and the value of n ranges from 2.3 to 2.44.

[0079] S4: Generate a microcirculatory vascular model based on the radius of the coronary artery outlet and the volume of the myocardium supplied by the coronary artery outlet, such as Figure 3 As shown, the specific process is as follows:

[0080] S41: Initialize and generate a microcirculatory vascular model, the microcirculatory vascular model includes N coronary artery outlets, each coronary artery outlet is used as a parent generation, and step S42 is executed;

[0081] S42: each parent generation performs a bifurcation operation, and one parent generation obtains multiple children, each of which is a blood vessel. The blood supply myocardium of the parent generation is allocated to each child generation, and all children generations are added to the microcirculation blood vessel model according to the corresponding relationship between the children and the parent generation;

[0082] A parent performs a fork operation as follows:

[0083] The blood supply myocardium of the parent generation is equivalent to an ellipsoid, and a point on the surface of the ellipsoid is taken as the root node. The root node represents the location of the parent generation's exit. The ellipsoid is evenly divided into m (2≤m≤5) sub-parts through the root node. The center of mass of each sub-part is found respectively, and the center of mass is connected with the root node. The m line segments obtained are m offspring. The volume of the blood supply myocardium of each offspring is the volume of one sub-part. The radius of the m offspring is the same, and the radius of the offspring is r 子代 The radius r of the parent 父代 Satisfies the relationship: m*(r 子代 ) n=(r 父代 ) n .

[0084] In this embodiment, when performing a bifurcation operation, the blood supply myocardium of the parent generation is equivalent to a sphere, and the sphere is evenly divided into two sub-parts through the root node.

[0085] A bifurcation operation is as follows: first, the blood supply myocardium of the parent generation is equivalent to a sphere, a point is taken on the surface of the sphere as the root node, and the ellipsoid is evenly divided into two hemispheres (sub-parts) through the root node. The center of mass of each hemisphere is found respectively, and the center of mass is connected with the root node. The two line segments obtained are two offspring (two blood vessels). The blood supply myocardium of each offspring is a hemisphere, and the radius of the two offspring is the same, and the radius of the offspring r 子代 The radius r of the parent 父代 Satisfies the relationship: 2*(r 子代 ) n =(r 父代 ) n .

[0086] S43: Traverse all the children obtained in the previous step, if there is a radius greater than r 0 The descendants of all the 0 The child of is taken as the parent, and step S42 is executed; otherwise, the generation of the small blood vessel tree model is completed;

[0087] Among them, r 0 is the preset minimum blood vessel radius of the microcirculation blood vessel model; in this embodiment, r 0 The size is 0.005mm.

[0088] S5: Based on the microcirculatory vascular model and routine blood test data, the microcirculatory resistance value of each coronary artery outlet is calculated using Poiseuille's theorem and Fallin's effect (including the reversal of Fallin's effect). The resistance value of each segment of blood vessel is calculated using Poiseuille's theorem, where the viscosity coefficient is obtained using the Fallin's effect, and the hematocrit in the Fallin's effect is determined by routine blood test data. The microcirculatory resistance value of each coronary artery outlet is calculated using the series-parallel theorem of resistance.

[0089] A method for calculating FFR comprises the following steps:

[0090] A1: Obtain a medical image of the heart, segment and reconstruct the medical image to obtain a coronary tree model, add p collateral vessels to the coronary tree model, and determine the volume of the myocardium and the radius of each coronary outlet;

[0091] A2: Based on the volume of the myocardium and the radius of each coronary artery outlet, the volume of the myocardium supplying blood to each coronary artery outlet is determined, a microcirculatory vascular model is generated, and the microcirculatory resistance value of each coronary artery outlet is calculated;

[0092] A3: Generate a computational fluid dynamics (CFD) computational grid, establish a three-dimensional CFD model of the coronary artery tree model and a one-dimensional CFD model of the microcirculation blood vessel model, and obtain the physical properties of the blood and the flow equation;

[0093] A4: Set the boundary conditions of the three-dimensional CFD model. The boundary conditions include inlet boundary conditions and outlet boundary conditions. Setting the boundary conditions includes the following steps:

[0094] A41: Set each inlet boundary condition of the three-dimensional CFD model to the blood pressure P of the corresponding coronary artery orifice 0 , and set each outlet boundary condition of the three-dimensional CFD model to a times (0 < a < 1) of the blood pressure of the corresponding coronary artery orifice, that is, the pressure P at each outlet of the three-dimensional CFD model = a * P 0 ; In this embodiment, the value of a is 0.7. In other embodiments, the value of a can be increased or decreased as needed.

[0095] A42: Obtain the current boundary conditions of the three-dimensional CFD model. For each outlet of the three-dimensional CFD model, solve the three-dimensional CFD model based on the physical properties of the blood and the flow equation to obtain the blood flow rate Q at each outlet of the three-dimensional CFD model;

[0096] A43: The inlets of the one-dimensional CFD model correspond one-to-one with the outlets of the three-dimensional CFD model. Set each inlet boundary condition of the one-dimensional CFD model to the blood flow rate Q at the corresponding outlet of the three-dimensional CFD model, and set each outlet boundary condition of the one-dimensional CFD model to the venous pressure Pout;

[0097] A44: Calculate the blood pressure Pin at each inlet of the one-dimensional CFD model according to the formula Pin - Pout = R * Q. If Pin is not equal to P and the difference is greater than the preset convergence accuracy, then correct each outlet boundary condition of the three-dimensional CFD model respectively. The correction formula is P` = (P * 4 + Pin) / 5, and repeat step A42. Otherwise, use the current boundary conditions of the three-dimensional CFD model as the finally set boundary conditions;

[0098] where, R represents the microcirculation resistance value, and P` represents the corrected outlet boundary condition of the three-dimensional CFD model;

[0099] A5: Based on the boundary conditions of the three-dimensional CFD model, the physical properties of the blood and the flow equation, solve to obtain the fluid parameters at each position of the coronary artery tree model, and calculate the fractional flow reserve (FFR) based on the obtained fluid parameters. The fluid parameters include flow rate, pressure and velocity.

[0100] A system for calculating FFR, such as Figure 2As shown, including:

[0101] A coronary tree model generation module is used to obtain a medical image of the heart, segment and reconstruct the medical image, obtain a coronary tree model, and add p side branches to the coronary tree model;

[0102] Microcirculatory vascular module, used to establish a microcirculatory vascular model and calculate the microcirculatory resistance value corresponding to each coronary artery outlet on the coronary tree model;

[0103] A computational grid generation module is used to generate computational fluid dynamics computational grids for the coronary tree model and the microcirculation blood vessel model, thereby establishing a three-dimensional CFD model of the coronary tree model and a one-dimensional CFD model of the microcirculation blood vessel model;

[0104] Boundary condition setting module, used to set the boundary conditions of the three-dimensional CFD model;

[0105] The property setting module is used to set the physical properties of blood and the flow equation. In the property setting module, based on the blood routine data and the Fallin effect formula, it is assumed that the blood is a Newtonian fluid or a generalized Newtonian fluid and uses laminar flow, blood density and blood viscosity that conform to individual specificity; the flow equation includes a steady flow equation or an unsteady flow equation, and the Navier-Stokes equations based on incompressible flow.

[0106] A solver solves the three-dimensional CFD model based on the boundary conditions of the three-dimensional CFD model, the physical properties of blood and the flow equations to obtain the fluid parameters at various locations in the coronary tree model;

[0107] The post-processing module performs post-processing based on the fluid parameters at each location of the coronary tree model to obtain the blood flow reserve fraction FFR. In the post-processing module, the mean arterial pressure Pd at each section of the coronary tree is calculated, and then divided by the mean arterial pressure Pa at the coronary orifice to obtain the blood flow reserve fraction FFR = Pd / Pa.

[0108] In this embodiment, in the post-processing module, multiple sections are cut on the coronary artery tree model, and the mean arterial pressure on each section is obtained, and then the mean arterial pressure is divided by the mean arterial pressure at the coronary artery orifice to obtain the blood flow reserve fraction of each section, wherein the mean pulsating pressure of a section is the mean pulsating pressure of the section in a cardiac cycle. The section selection position includes between the upper and lower bifurcations of the coronary artery.

[0109] In actual application, the coronary tree model generation module analyzes and segments the blood vessels in the patient's medical images (such as various medical images that comply with DICOM specifications). Various open source software such as vmtk (The Vascular Modeling Toolkit) can be used to calculate and reconstruct the blood vessel centerline and blood vessel wall based on the results of the analysis and segmentation of the blood vessels in the medical images, thereby forming a coronary tree model.

[0110] The computational grid generation module can utilize various open source software such as vmtk to generate high-quality computational grids that meet CFD calculation requirements for the coronary tree model, thereby establishing a three-dimensional CFD model of the coronary tree model.

[0111] In the prior art, the boundary condition setting module can only set the inlet boundary condition of the three-dimensional CFD model by statistically or assuming the flow ratio at the inlet of the left and right aortas. This boundary condition setting method cannot reflect the individual specificity, and the statistically or hypothetically obtained inlet boundary condition may not be applicable to all individuals, resulting in a decrease in the accuracy of the CFD calculation results.

[0112] The present application adds collateral vessels to the coronary artery tree model, so that the obtained coronary artery tree model is more consistent with the actual physiological situation, and then assumes that the blood vessels are constantly bifurcated to obtain a microcirculatory vascular model, and the microcirculatory resistance is calculated with high accuracy. When setting the boundary conditions, the outlet boundary conditions are iteratively determined according to the calculated microcirculatory resistance, and the outlet boundary conditions that are more consistent with the actual physiological situation are obtained, thereby improving the accuracy of calculating the blood flow reserve fraction.

[0113] This application calculates FFR without the support of invasive medical data, which reduces medical costs and avoids the risks of invasive testing. At the same time, the coronary artery tree model constructed by this application can accurately predict the effect of coronary treatment, which is helpful for planning clinical treatment plans.

[0114] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for calculating coronary terminal microvascular resistance, characterized in that: The following steps are involved: S1: acquiring routine blood data and medical images of the heart, performing segmentation and reconstruction processing on the medical images, and obtaining a coronary tree model, wherein the coronary tree model includes the aorta root, and determining the volume of the myocardium and the radius of each coronary outlet based on the coronary tree model; S2: Add multiple side branches to the coronary tree model, that is, add multiple coronary artery outlets; S3: for the N coronary artery outlets on the coronary artery tree model, based on the volume of the myocardium and the radius of each coronary artery outlet, the volume of the myocardium supplied by each coronary artery outlet is determined respectively; S4: Generate a microcirculatory vascular model based on the radius of the coronary artery outlet and the volume of the myocardium supplied by the coronary artery outlet. The specific process is as follows: S41: Initialize and generate a microcirculatory vascular model, wherein the microcirculatory vascular model includes N coronary artery outlets, and each coronary artery outlet is used as a parent generation, and step S42 is executed; S42: each parent generation performs a bifurcation operation, and one parent generation obtains multiple children, each of which is a blood vessel. The blood supply myocardium of the parent generation is allocated to each child generation, and all children generations are added to the microcirculation blood vessel model according to the corresponding relationship between the children and the parent generation; S43: Traverse all the children obtained in the previous step, if there is a radius greater than , then all the children with a radius greater than The child of is taken as the parent, and step S42 is executed; otherwise, the generation of the small blood vessel tree model is completed; in, The minimum vessel radius of the pre-set microcirculation vascular model; S5: Based on the microcirculatory vascular model and routine blood data, the microcirculatory resistance value of each coronary artery outlet is calculated using Poiseuille's theorem and Fallin effect; In the step S2, p (1≤p≤7) side branches are added to the coronary artery tree model, the side branches are added at a side of the coronary artery close to the heart and between the upper and lower bifurcations of the existing coronary artery, the length of the side branches is 3-5 mm, and the radius of the side branches is the minimum radius of the existing blood vessels on the coronary artery tree model; The value of p is determined by the change in the blood vessel area between the upper and lower bifurcations, specifically: ， in, represents the radius of the collateral vessel, represents the radius of the vessel downstream of the superior bifurcation, represents the radius of the upstream vessel of the lower bifurcation, and the value range of n is 2.3-2.44; In step S3, the calculation formula for the volume of the myocardium supplied by the i-th (1≤i≤N) coronary artery outlet is as follows: ， in, represents the volume of the myocardium supplied by the i-th coronary artery outlet, The volume of myocardium, represents the radius of the i-th coronary artery outlet, represents the radius of the kth coronary artery outlet, and the value of n ranges from 2.3 to 2.44; In step S42, a parent generation performs a fork operation as follows: The blood supply myocardium of the parent generation is equivalent to an ellipsoid, and a point on the surface of the ellipsoid is taken as the root node. The root node represents the location of the parent generation's exit. The ellipsoid is evenly divided into m (2≤m≤5) sub-parts through the root node. The center of mass of each sub-part is found respectively, and the center of mass is connected with the root node. The m line segments obtained are m offspring. The volume of the blood supply myocardium of each offspring is the volume of one sub-part. The radius of the m offspring is the same, and the radius of the offspring is Radius with parent Satisfies the relationship: m* .

2. The method for calculating the coronary artery terminal microvascular resistance according to claim 1, characterized in that: When performing a bifurcation operation, the parent myocardium is equivalent to a sphere.

3. The method for calculating the coronary artery terminal microvascular resistance according to claim 1, characterized in that: When performing a bifurcation operation, the ellipsoid is divided into two equal parts through the root node.

4. The method for calculating the coronary artery terminal microvascular resistance according to claim 1, characterized in that: In step S43, the preset minimum blood vessel radius of the microcirculation blood vessel model The size is 0.005mm.

5. A method for calculating FFR, characterized in that: Calculating microvascular resistance based on the method for calculating coronary artery end microvascular resistance as claimed in any one of claims 1 to 4 to set boundary conditions comprises the following steps: A1: Obtain a medical image of the heart, segment and reconstruct the medical image to obtain a coronary tree model, add p collateral vessels to the coronary tree model, and determine the volume of the myocardium and the radius of each coronary outlet; A2: Based on the volume of the myocardium and the radius of each coronary artery outlet, the volume of the myocardium supplying blood to each coronary artery outlet is determined, a microcirculatory vascular model is generated, and the microcirculatory resistance value of each coronary artery outlet is calculated; A3: Generate computational fluid dynamics computational grid, build a three-dimensional CFD model of the coronary artery tree model and a one-dimensional CFD model of the microcirculation vascular model, and obtain the physical properties and flow equations of blood; A4: Set the boundary conditions of the 3D CFD model. The boundary conditions include inlet boundary conditions and outlet boundary conditions. Setting boundary conditions includes the following steps: A41: Set each inlet boundary condition of the three-dimensional CFD model to the blood pressure P0 of the corresponding coronary ostium, and set each outlet boundary condition of the three-dimensional CFD model to a times (0 < a < 1) of the blood pressure of the corresponding coronary ostium, that is, the pressure P at each outlet of the three-dimensional CFD model a * P0; A42: obtaining the current boundary conditions of the three-dimensional CFD model, solving the three-dimensional CFD model for each outlet of the three-dimensional CFD model based on the physical properties of blood and the flow equation, and obtaining the blood flow Q at each outlet of the three-dimensional CFD model; A43: The inlet of the one-dimensional CFD model corresponds to the outlet of the three-dimensional CFD model one by one, and each inlet boundary condition of the one-dimensional CFD model is set to the blood flow Q at the outlet of the corresponding three-dimensional CFD model, and each outlet boundary condition of the one-dimensional CFD model is set to the venous pressure Pout; A44: According to the formula Pin-Pout R*Q calculates the blood pressure Pin at each inlet of the one-dimensional CFD model. If Pin and P are not equal and the difference is greater than the preset convergence accuracy, each outlet boundary condition of the three-dimensional CFD model is corrected respectively. The correction formula is P` (P*4 Pin) / 5, repeat step A42, otherwise, use the current boundary conditions of the three-dimensional CFD model as the final boundary conditions; Among them, R represents the microcirculation resistance value, and P` represents the outlet boundary condition of the modified three-dimensional CFD model; A5: Based on the boundary conditions of the three-dimensional CFD model, the physical properties of blood and the flow equation, the fluid parameters at each position of the coronary tree model are solved, and the blood flow reserve fraction FFR is calculated based on the solved fluid parameters.

6. A FFR calculation system, characterized in that: Based on the calculation method as claimed in claim 5, comprising: A coronary tree model generation module is used to obtain a medical image of the heart, segment and reconstruct the medical image, obtain a coronary tree model, and add p side branches to the coronary tree model; Microcirculatory vascular module, used to establish a microcirculatory vascular model and calculate the microcirculatory resistance value corresponding to each coronary artery outlet on the coronary tree model; A computational grid generation module, used to generate computational fluid dynamics computational grids for the coronary tree model and the microcirculation blood vessel model, thereby establishing a three-dimensional CFD model of the coronary tree model and a one-dimensional CFD model of the microcirculation blood vessel model; Boundary condition setting module, used to set the boundary conditions of the three-dimensional CFD model; Property setting module, used to set the physical properties and flow equations of blood; A solver, which solves the three-dimensional CFD model based on the boundary conditions of the three-dimensional CFD model, the physical properties of blood and the flow equation, and obtains the fluid parameters at various locations of the coronary tree model; The post-processing module performs post-processing based on the fluid parameters at various locations in the coronary tree model to obtain the blood flow reserve fraction FFR.

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