Method and system for obtaining coronary microcirculation vascular resistance based on layered myocardial model

Abstract

The application relates to a coronary microcirculation vascular resistance acquisition method and system based on a layered myocardial model, which comprises the following steps: establishing a coronary vessel model from medical images; generating a side vessel for the coronary artery; regarding the coronary artery and the side vessel as main vessels, fitting and constructing an outer surface of a myocardial model according to the outlet position of the main vessels, establishing an inner surface of the myocardial model based on a similar principle to the outer surface, and ensuring that the volume of the model is the myocardial volume value; using an ellipsoid surface for layered interpolation; selecting a point P in the outermost layer and connecting the main vessel outlet to generate a microcirculation vessel; selecting a point T outside the current layer and cooperating with the nearest microcirculation vessel to generate a bifurcated microcirculation vessel; gradually advancing to the inner layer to form bifurcation and ensure the bifurcation number of each layer; and calculating the resistance value of the main vessel outlet. Compared with the prior art, the application considers the distribution of the coronary artery at various levels of the myocardium under real conditions, so that the calculated resistance value is more accurate and has the specificity of a patient.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of blood vessel resistance acquisition, in particular to a coronary microcirculation blood vessel resistance acquisition method and system based on a layered myocardial model. BACKGROUND

[0002] The main cause of coronary heart disease is coronary 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 region supplied by the coronary artery to the maximum blood flow that can be obtained by the same region under normal conditions. It can be simplified as the ratio of the average pressure (Pd) in the distal coronary artery to the average pressure (Pa) of the aortic orifice under the maximum hyperemia state of the myocardium. FFR can indicate the influence of coronary stenosis on the distal blood flow, and is used to assess whether the myocardium is ischemic. FFR has become a recognized indicator for functional evaluation of coronary stenosis.

[0003] When determining FFR, the blood flow velocity under the maximum hyperemia state of the myocardium and the average pressure of the aortic orifice at the coronary artery are needed to calculate FFR by obtaining the average pressure in the distal coronary artery through different means. At present, the FFR acquisition method is mostly invasive, which has high risk and is expensive. In order to solve the above problems, researchers have proposed a non-invasive FFR measurement method combining coronary CTA and computational fluid dynamics (CFD);

[0004] A system and method for simulating and calculating fractional flow reserve by using computational fluid dynamics are disclosed in the authorized announcement No. CN106650267B. The system includes: a blood vessel tree model generation module that obtains medical images, performs segmentation, and reconstructs the geometric model of the individual's blood vessel tree; a computational grid generation module that generates a computational grid for the geometric model and establishes a CFD model of the blood vessel tree; a boundary condition setting module that sets the corresponding inlet and outlet boundary conditions for the CFD model of the blood vessel tree; an attribute setting module that sets the physical properties of blood and the flow equation; a solver that solves the CFD model of the blood vessel tree based on the inlet and outlet boundary conditions, the set physical properties, and the flow equation to obtain the fluid parameters at each place of the blood vessel tree; and a post-processing module that post-processes the fluid parameters to obtain the fractional flow reserve. The inlet and outlet boundary conditions are both individual-specific.

[0005] The outlet boundary condition is the microvascular resistance at each outlet of the individual's blood vessel tree. Currently, the calculation of microvascular resistance generally uses a pressure guide wire with a temperature sensor to measure relevant parameters and then obtain the coronary microvascular resistance index value. However, the process of using a pressure guide wire with a temperature sensor to measure relevant parameters and then obtaining the coronary microvascular resistance index requires complex operations by the doctor, greatly increasing the workload of the doctor.

[0006] To solve this problem, the invention disclosed in CN111627002A discloses a coronary microvascular resistance index calculation device and method. The coronary microvascular resistance index calculation device comprises: an aortic pressure acquisition module for acquiring aortic pressure; a DSA image acquisition module for acquiring a coronary DSA image sequence; a change curve generation module connected with the DSA image acquisition module, for generating a contrast agent area change curve according to the imaging area of the contrast agent in a plurality of target frames and the imaging time of the target frames; a curve slope acquisition module connected with the change curve generation module, for acquiring the average slope of the contrast agent area change curve; a resistance index calculation module connected with the aortic pressure acquisition module and the curve slope acquisition module, for calculating the coronary microvascular resistance index according to the aortic pressure and the average slope.

[0007] This method calculates the coronary microvascular resistance index through the average slope of the contrast agent area change curve and the aortic pressure. The measurement of the contrast agent area and the aortic pressure both have large measurement errors, and the coronary microvascular is difficult to capture from the coronary DSA image sequence, making it difficult to ensure the accuracy of the obtained coronary microvascular and its resistance. SUMMARY

[0008] The purpose of the present application is to overcome the above-mentioned defects of the prior art, and to provide a layered myocardial model-based coronary microcirculation vascular resistance acquisition method and system that takes into account the distribution of the coronary artery between each level of the myocardium under real conditions.

[0009] The purpose of the present application can be achieved by the following technical solutions:

[0010] A layered myocardial model-based coronary microcirculation vascular resistance acquisition method, comprising the following steps:

[0011] S1: Obtain medical images, extract the cross section where the coronary vessel model and the aortic root are located, and the total volume of the myocardium;

[0012] S2: Generate collateral vessels upstream and downstream of each coronary artery in the coronary vessel model;

[0013] S3: Treat all the coronary arteries and collateral vessels as main vessels, and obtain the position coordinates and vessel radius of the outlet of each main vessel;

[0014] S4: According to the position coordinates of the outlet of each main vessel, an ellipsoidal equation is fitted to construct an outer myocardial wall equation, and then combined with the cross section where the aortic root is located, an outer myocardial wall surface is obtained;

[0015] S5: based on the principle that the outer myocardial wall surface is similar to the inner myocardial wall surface, a myocardial inner wall surface is constructed according to the outer myocardial wall surface, and the volume surrounded by the outer myocardial wall surface, the inner myocardial wall surface and the cross section where the aortic root is located is equal to the total volume of the myocardium, thereby constituting a myocardial model;

[0016] S6: using an ellipsoid surface for interpolation in the inner layer of the myocardial model, and assigning a thickness to each layer;

[0017] S7: meshing each layer of the myocardial model respectively to obtain a point cloud file of each layer;

[0018] S8: randomly selecting a point P in the outermost layer point cloud file of the myocardial model, pre-connecting the point P with each main blood vessel outlet, and selecting a connection to generate a blood vessel from the pre-connection according to the principle of generating the minimum total volume of the blood vessel, as a microcirculation blood vessel;

[0019] S9: repeating step S8 until a segment of microcirculation blood vessel is generated for each main blood vessel outlet;

[0020] S10: randomly selecting a point T in the current layer and the myocardial model point cloud file outside the current layer, pre-connecting the m microcirculation blood vessels closest to the point T, and selecting a point K to connect the point T and the upstream and downstream of the pre-connected microcirculation blood vessel according to the principle that the total pressure drop of each branch under the same main blood vessel outlet is equal and the total volume of the microcirculation blood vessel is minimum, to generate a branched multiple microcirculation blood vessel, and set the blood vessel radius of each newly generated microcirculation blood vessel according to the area bifurcation power law rule; comparing the total volume of the blood vessel tree formed after all pre-connections, and retaining the pre-connection with the minimum total volume of the blood vessel tree, the blood vessel tree including coronary arteries, collateral vessels and microcirculation blood vessels;

[0021] S11: repeating step S10 until the number of bifurcations of the newly generated branched multiple microcirculation blood vessels in the point cloud file of the myocardial model of the layer reaches the preset bifurcation number;

[0022] S12: taking a layer inside the current layer as the current layer, repeating step S11, and gradually advancing to the innermost layer until the radius of all blood vessel outlets in the generated blood vessel tree is less than the preset blood vessel threshold;

[0023] S13: calculating the resistance value of each outlet of the main blood vessel according to the blood vessel tree obtained in step S12.

[0024] Further, in step S6, the thickness of each layer is assigned in a linear manner from the inside to the outside.

[0025] Further, in step S10, the blood vessel radius of each newly generated microcirculation blood vessel is set according to the area bifurcation power law rule, which is:

[0026] The generated bifurcated microcirculation vessels include K-upstream vessels, K-downstream vessels and K-T vessels, the vessel radius of the K-upstream vessels is equal to the vessel radius of the outlet of the main vessel, the vessel radius of the K-downstream vessels and the K-T vessels are equal, and the calculation expression of the vessel radius of the K-downstream vessels and the K-T vessels is:

[0027]

[0028] In the formula, R T is the vessel radius of the K-T vessels, R P is the vessel radius of the K-downstream vessels, and R i is the vessel radius of the K-upstream vessels, and γ is a bifurcation power law.

[0029] Further, the selected point K is determined according to the principle that the total pressure drop of each branch under the outlet of the same main vessel is equal and the principle that the total volume of the microcirculation vessels is minimum, and the selected point K is specifically:

[0030] According to the principle that the total pressure drop of each branch under the outlet of the same main vessel is equal, the length and the cross-sectional area of the vessels connected to the upstream and the downstream of the microcirculation vessels at the selected point K are the same; according to the principle that the total volume of the microcirculation vessels is minimum, the selected point K satisfies the total volume minimum of the vessels connected to the point T, the upstream and the downstream of the microcirculation vessels.

[0031] Further, the step S2 is specifically:

[0032] The number of the increased collateral vessels, the vessel radius of each collateral vessel and the corresponding bifurcation power law are determined according to the vessel radius of the upstream and the downstream of each coronary vessel in the coronary vessel model, and the increased collateral vessels are uniformly distributed at the upstream and the downstream of the corresponding coronary vessel.

[0033] The relationship between the number of the increased collateral vessels, the vessel radius of each collateral vessel and the corresponding bifurcation power law is:

[0034] Rh γ -Rd γ =n×R γ

[0035] In the formula, Rh is the vessel radius of the upstream of the coronary vessel, Rd is the vessel radius of the downstream of the coronary vessel, γ is the bifurcation power law, n is the number of the collateral vessels, and R is the vessel radius of the collateral vessels.

[0036] Further, the method for acquiring the coronary terminal microcirculation vascular resistance further comprises: acquiring a region of a cardiac cavity, and if a pre-connected blood vessel passes through the region of the cardiac cavity in the pre-connection process in step S8 and step S10, discarding the pre-connection.

[0037] If the radius of the generated microcirculation blood vessel is less than half of the blood vessel threshold in step S10, the pre-connection of the corresponding microcirculation blood vessel is discarded.

[0038] Further, in step S13, the resistance value of each outlet of the main blood vessel is specifically calculated as follows: the resistance of each microcirculation blood vessel is calculated based on Poiseuille's theorem, and then the resistance of each blood vessel outlet in the blood vessel tree is calculated according to the series-parallel connection rule, the resistance is equivalent to the resistance, and the calculation expression of the resistance of each microcirculation blood vessel is as follows:

[0039]

[0040] In the formula, R is the resistance, μ is the viscosity of blood, L is the length of the blood vessel, and A is the cross-sectional area of the blood vessel.

[0041] Further, in step S13, the resistance value of each outlet of the main blood vessel is specifically calculated as follows:

[0042] The resistance of each blood vessel outlet in the blood vessel tree is determined by calculating the capacitance and / or inductance of each blood vessel, and the calculation expression of the capacitance of the blood vessel is as follows:

[0043]

[0044] In the formula, C is the capacitance, A is the cross-sectional area of the blood vessel, L is the length of the blood vessel, ρ is the density of blood, and a is the pulse wave velocity.

[0045] The calculation expression of the inductance of the blood vessel is as follows:

[0046]

[0047] In the formula, I is the inductance.

[0048] Further, the resistance of each blood vessel outlet in the blood vessel tree acquired in step S13 is used to set the outlet boundary condition of the three-dimensional CFD model of the blood vessel tree.

[0049] The application also provides a coronary microcirculation vascular resistance acquisition system based on a layered myocardial model, comprising a memory and a processor, the memory stores a computer program, and the processor calls the computer program to execute the steps of the method as described above.

[0050] Compared with the prior art, the application has the following advantages:

[0051] (1) The present application fully considers the distribution of the coronary artery between each level of the myocardium under the real situation in the process of establishing the microcirculation vascular tree model, and extracts the parameters such as the myocardial volume, the coronary trunk running, and the coronary cross-sectional area with patient specificity, establishes a layered myocardial model, respectively grows the microcirculation vessels in each layer of the myocardial model, and ensures the number of newly added branches in each layer, so that the resistance value calculated based on the microcirculation vascular model is more accurate and has patient specificity.

[0052] The resistance value calculated by the method makes the numerical simulation model for calculating the flow reserve fraction have relatively accurate and patient-specific outlet boundary conditions, so that the coronary FFR obtained by numerical simulation is more accurate.

[0053] (2) The present application considers that the coronary vessels can be obtained through medical images such as CTA images, but the existing medical images are not accurate enough to clearly observe the collateral vessels and the microcirculation vessels at the end of the coronary artery, therefore, the present application regenerates the collateral vessels and the microcirculation vessels at the end of the coronary artery based on the myocardium and the coronary vessels according to the distribution law of the collateral vessels and the microcirculation vessels at the end of the coronary artery, so as to calculate the resistance of the microcirculation vessels at the end of the coronary artery, which can greatly improve the accuracy of the calculation result.

[0054] (3) The radius of all vessel outlets in the vascular tree is generally less than a vessel threshold, and the reduction of the vessel radius is generally realized by branching and according to the area branching power law rule; to generate branched vessels, the present application first randomly selects a point P in the point cloud file of the myocardial model to connect with the main body vessel outlet to generate microcirculation vessels; then randomly selects a point T to connect with the nearby microcirculation vessels, forms a three-point combination of the point T, the upstream and the downstream in a certain microcirculation vessel, selects a point K to connect with the point T, the upstream and the downstream in a certain microcirculation vessel according to the principle that the total pressure drops of each branch are equal, forms a plurality of branched microcirculation vessels, and thus the coronary microcirculation vessels obtained from the coronary microcirculation vessels are close to the real coronary microcirculation vessel distribution characteristics in terms of geometry and function.

[0055] (4) The present application determines the starting point of the microcirculation vessel growth and the initial cross-sectional area of the microcirculation vessel based on the coronary trunk with patient-specific increased collateral vessels, generates the coronary microcirculation vessel model inside the extracted myocardial model, fully considers the blood supply condition of the coronary artery to the myocardium, so that the microcirculation vessel model established is close to the real coronary microcirculation vessel distribution characteristics in terms of geometry and function, and the resistance value calculated based on the microcirculation vessel model is more accurate and has patient specificity. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1A flowchart of a method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model is provided in the embodiments of the present application.

[0057] Figure 2 A schematic diagram of coronary vessels, collateral vessels and coronary end microcirculation vessels is provided in the embodiments of the present application.

[0058] Figure 3 A coronary vessel model schematic diagram is provided in the embodiments of the present application. DETAILED DESCRIPTION

[0059] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0060] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0061] Embodiment 1

[0062] The embodiment provides a method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model, comprising the following steps:

[0063] S1: Obtain medical images, and extract a cross section where a coronary vessel model and an aortic root are located and a total myocardial volume;

[0064] The present application considers that the coronary vessels, the coronary vessel distribution and the like shown in FIG. 1 can be obtained through medical images such as CTA images, but the existing medical image accuracy is not enough, and it is difficult to clearly observe the collateral vessels and the coronary end microcirculation vessels, so the present application regenerates the collateral vessels and the coronary end microcirculation vessels based on the myocardium and the coronary vessels according to the distribution law of the collateral vessels and the coronary end microcirculation vessels, with the purpose of constructing the vessel distribution as shown in FIG. 2, so as to calculate the resistance of the coronary end microcirculation vessels, which can greatly improve the accuracy of the calculation result. Figure 3 Figure 2 S2: Generate collateral vessels upstream and downstream of each coronary vessel in the coronary vessel model;

[0065] Step S2 is specifically:

[0066] Step S2 is specifically:

[0067] ​The increased number of collateral vessels, the vessel radius of each collateral vessel and the corresponding bifurcation power law are determined according to the vessel radius of each coronary artery upstream and downstream in the coronary vessel model, and the increased number of collateral vessels is uniformly distributed upstream and downstream of the corresponding coronary artery;

[0068] The relationship of the increased number of collateral vessels, the vessel radius of each collateral vessel and the corresponding bifurcation power law is:

[0069] Rh γ -Rd γ =n×R γ

[0070] In the formula, Rh is the upstream vessel radius of the coronary artery, Rd is the downstream vessel radius of the coronary artery, γ is the bifurcation power law, n is the number of collateral vessels, and R is the vessel radius of the collateral vessel.

[0071] S3: All coronary arteries and collateral vessels are regarded as main vessels, and the position coordinates and vessel radius of the outlet of each main vessel are obtained;

[0072] S4: According to the position coordinates of the outlet of each main vessel, an equation of the outer myocardial wall is fitted and constructed by using an ellipsoid equation, and then the outer myocardial wall surface is obtained in combination with the cross section where the aortic root is located;

[0073] S5: Based on the similar principle of the outer myocardial wall surface and the inner myocardial wall surface, the inner myocardial wall surface is constructed according to the outer myocardial wall surface, and the volume enclosed by the outer myocardial wall surface, the inner myocardial wall surface and the cross section where the aortic root is located is equal to the total volume of the myocardium, so as to form a myocardial model;

[0074] S6: The ellipsoid surface is used for interpolation in the inner layer of the myocardial model, and each layer is assigned a thickness;

[0075] S7: Each layer of the myocardial model is respectively meshed to obtain a point cloud file of each layer;

[0076] S8: A point P is randomly selected in the outermost layer point cloud file of the myocardial model, the point P is pre-connected with the outlets of each main vessel, and according to the principle of generating the minimum total volume of vessels, a segment of vessel is selected from the pre-connection to generate a microcirculation vessel;

[0077] S9: Step S8 is repeated until a segment of microcirculation vessel is generated for each outlet of the main vessel;

[0078] S10: randomly selecting a point T in the point cloud file of the myocardial model of the current layer and outside the current layer, pre-connecting m microcirculation blood vessels closest to the point T, for each pre-connected microcirculation blood vessel, selecting a point K to connect the point T, an upstream and a downstream in the microcirculation blood vessel according to the principle that the total pressure drop of each branch under the same main vessel outlet is equal and the total volume of the microcirculation blood vessel is minimum, then selecting to delete or not to delete the microcirculation blood vessel, finally generating a plurality of microcirculation blood vessels of bifurcation type, and setting the blood vessel radius of each newly generated microcirculation blood vessel in combination with the area bifurcation power law; comparing the total volume of the blood vessel trees composed after all pre-connections, and retaining the pre-connection with the minimum total volume of the blood vessel tree, the blood vessel tree including coronary arteries, collateral vessels and microcirculation blood vessels;

[0079] The principle that the total pressure drop of each branch under the same main vessel outlet is equal and the total volume of the microcirculation blood vessel is minimum for selecting the point K is specifically:

[0080] According to the principle that the total pressure drop of each branch under the same main vessel outlet is equal, the length and cross-sectional area of the blood vessels connected by the selected point K to the upstream and downstream in the microcirculation blood vessel are the same; according to the principle that the total volume of the microcirculation blood vessel is minimum, the selected point K satisfies the total volume minimum of the blood vessels connected to the point T, the upstream and the downstream in the microcirculation blood vessel.

[0081] The setting of the blood vessel radius of each newly generated microcirculation blood vessel in combination with the area bifurcation power law is specifically:

[0082] The generated plurality of microcirculation blood vessels of bifurcation type include K-upstream blood vessels, K-downstream blood vessels and K-T blood vessels, the blood vessel radius of the K-upstream blood vessels is equal to the blood vessel radius of the main vessel outlet, the blood vessel radius of the K-downstream blood vessels and the K-T blood vessels is equal, and the calculation expression of the blood vessel radius of the K-downstream blood vessels and the K-T blood vessels is:

[0083]

[0084] In the formula, R T is the blood vessel radius of the K-T blood vessel, R P is the blood vessel radius of the K-downstream blood vessel, and R i is the blood vessel radius of the K-upstream blood vessel, and γ is the bifurcation power law.

[0085] S11: repeating step S10 until the number of bifurcations of the newly generated plurality of microcirculation blood vessels of bifurcation type in the point cloud file of the myocardial model of the layer reaches the preset bifurcation number;

[0086] S12: taking a layer inside the current layer as the current layer, repeating step S11, and gradually advancing to the innermost layer until the radius of all blood vessel outlets in the generated blood vessel tree is less than the preset blood vessel threshold.

[0087] The radius of all the blood vessel outlets in the blood vessel tree is generally less than a blood vessel threshold, and the reduction of the blood vessel radius is generally achieved by bifurcation and according to an area bifurcation power law rule; to generate bifurcated blood vessels, the application first randomly selects a point P in a point cloud file of a myocardial model to connect with a main body blood vessel outlet to generate microcirculation blood vessels; then randomly selects a point T to connect with nearby microcirculation blood vessels to form a three-point combination of the point T, an upstream point and a downstream point in a certain microcirculation blood vessel, according to the principle that the total pressure drops of each branch are equal, selects a point K to connect with the point T, the upstream point and the downstream point in the certain microcirculation blood vessel to form a plurality of bifurcated microcirculation blood vessels, and thus the coronary terminal microcirculation blood vessels obtained by the method are close to the real coronary microcirculation blood vessel distribution characteristics in terms of geometry and function. The blood vessels generated in the method are all assumed to be linear and have circular cross sections.

[0088] S13: Calculate the resistance values of each outlet of the main body blood vessels according to the blood vessel tree obtained in step S12.

[0089] In step S13, the resistance values of each outlet of the main body blood vessels are calculated as follows: the resistance of each microcirculation blood vessel is calculated based on the Poiseuille theorem, and then the resistance of each blood vessel outlet in the blood vessel tree is calculated according to the series-parallel connection rule. The resistance is equivalent to the resistance, and the calculation expression of the resistance of each microcirculation blood vessel is as follows:

[0090]

[0091] In the formula, R is the resistance, μ is the blood viscosity, L is the blood vessel length, and A is the cross-sectional area of the blood vessel.

[0092] In step S13, the method of steps S1-S12 can also be used to calculate the capacitance and / or inductance of the blood vessels, so as to calculate the resistance of each blood vessel outlet. The calculation of the resistance, capacitance and inductance of the blood vessel outlet has been disclosed in the prior art, and the application focuses on providing a specific calculation method of the resistance, capacitance and inductance of the blood vessel, which is more accurate.

[0093] The resistance values of each outlet of the main body blood vessels are calculated as follows:

[0094] The resistance of each blood vessel outlet in the blood vessel tree is determined by calculating the capacitance and / or inductance of each blood vessel, and the calculation expression of the capacitance of the blood vessel is as follows:

[0095]

[0096] In the formula, C is the capacitance, A is the cross-sectional area of the blood vessel, L is the blood vessel length, ρ is the blood density, and a is the pulse wave velocity.

[0097] The calculation expression of the inductance of the blood vessel is as follows:

[0098]

[0099] wherein I is an inductance.

[0100] The method further comprises: obtaining a region of a cavity of the heart by the medical image, and if the pre-connected blood vessel passes through the region of the cavity of the heart, discarding the pre-connection in the pre-connection process in step S8 and step S10.

[0101] If the radius of the generated microcirculation blood vessel is less than half of the blood vessel threshold in step S10, discarding the pre-connection of the corresponding microcirculation blood vessel.

[0102] In summary, the method fully considers the distribution of the coronary artery between each layer of the myocardium in the real situation, and extracts the patient-specific myocardial volume, the running of the coronary trunk, the coronary cross-sectional area and other parameters, establishes a layered myocardial model, grows the microcirculation blood vessels in each layer of the myocardial model, and ensures the number of newly added branches in each layer, so that the resistance value calculated based on the microcirculation blood vessel model is more accurate and has the specificity of the patient.

[0103] The method determines the starting point of the microcirculation blood vessel growth and the initial cross-sectional area of the microcirculation blood vessel based on the coronary trunk with patient-specific increased collateral blood vessels, generates the coronary microcirculation blood vessel model inside the extracted myocardial model, fully considers the blood supply of the coronary artery to the myocardium, so that the established microcirculation blood vessel model is close to the real coronary microcirculation blood vessel distribution characteristics in geometry and function, and the resistance value calculated based on the microcirculation blood vessel model is more accurate and has the specificity of the patient.

[0104] The resistance value calculated by the method makes the numerical simulation model for calculating the flow reserve fraction have relatively accurate and patient-specific outlet boundary conditions, so that the coronary FFR obtained by numerical simulation is more accurate.

[0105] The embodiment also provides a coronary microcirculation blood vessel resistance acquisition system based on a layered myocardial model, comprising a memory and a processor, the memory stores a computer program, and the processor calls the computer program to execute the steps of the coronary microcirculation blood vessel resistance acquisition method based on the layered myocardial model.

[0106] The specific implementation process of the coronary microcirculation blood vessel resistance acquisition method based on the layered myocardial model in the embodiment is as follows:

[0107] (1) Obtain the corresponding coronary blood vessel model and the cross section of the aortic root from the CTA image.

[0108] (2) Determine the number of increased collateral vessels n (1-7) and the area of each collateral A and the corresponding bifurcation power law γ (1.7-3) according to the upstream (Ap) and downstream (Ad) area of each coronary artery.

[0109] Ap γ -Ad γ = n x A γ

[0110] (3) The increased collateral vessels are evenly distributed between the upstream and downstream.

[0111] (4) Obtain the area and position coordinates of each coronary artery outlet (including the newly added collateral vessels).

[0112] (5) Use the position coordinates obtained in step (4) to fit the myocardial outer wall equation based on the ellipsoid equation, and use the cross section in (1) to obtain the final myocardial outer wall surface.

[0113] (6) Based on the principle of similarity, construct the myocardial inner wall surface ellipsoid, so that the volume of the part surrounded by the two surfaces and the cross section in (1) is equal to the total volume of the myocardium. The space surrounded by the three surfaces is the final myocardial model.

[0114] (7) Use ellipsoid interpolation to perform layering operation on the obtained myocardial model, from inside to outside, and assign thickness to each layer in a linearly varying manner. Linear variation factor range: 0-2, total layer number: 10-30.

[0115] (8) Mesh the myocardial model of each layer to obtain the respective point cloud files.

[0116] (9) The angiogenesis process is from the outermost layer to the innermost layer. When the radius of all outlet segments (terminal) of the generated vascular tree model is less than a threshold r min (2μm-10μm), the generation of the entire coronary vascular model is completed.

[0117] (10) Randomly select a point P in the point cloud model of the outermost myocardium as the outlet point of the generated vascular segment. Connect P with each coronary outlet (area A i ) (directly discarded by passing through the cavity), and the length of the obtained vessel is L i , and then select the connection as a segment of the generated microcirculation vessel (the area of the vessel is the area of the selected coronary outlet) by the principle of minimum total vessel volume.

[0118] (11) Repeat step (10) until a segment of microcirculation vessel is generated for each outlet.

[0119] (12) Continue to randomly select point T in the myocardial model, and screen m microcirculation vessels closest to point T to perform pre-connection (directly discard the case of passing through the cavity). According to the principle of equal total pressure drop of each branch under the same coronary artery outlet, in combination with the area bifurcation power law rule, find the bifurcation point in the myocardium that makes the total volume of the vascular tree under this connection condition minimum, complete the optimization under this connection, and take it as the preliminary connection result. Then compare the total volume of the vascular tree generated by all pre-connections, and take the minimum case as the final optimization result (if the vascular radius generated by this connection is less than half of the threshold in (9), discard this case).

[0120] (13) Repeat step (12) until at least N times (2-10) of bifurcation from the upper layer to the layer, and gradually advance to the innermost layer until the termination condition is met.

[0121] (14) Calculate the resistance (resistance R) of each generated blood vessel based on Poiseuille's theorem, and then calculate the equivalent resistance value of each coronary artery outlet in combination with the series-parallel connection rule of resistance. Calculate the compliance (capacitance C) and inertia (inductance I) of each generated blood vessel by the following formula, and then calculate the equivalent capacitance and equivalent inductance of each coronary artery outlet in combination with the series-parallel connection rule. (A, L, μ, ρ, a represent the cross-sectional area of the blood vessel, the length of the blood vessel, the viscosity of the blood, the density of the blood, and the pulse wave velocity, respectively).

[0122]

[0123]

[0124]

[0125] The preferred embodiments of the application are described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and changes without creative work based on the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment based on the prior art by those skilled in the art in the technical field in accordance with the concept of the present application shall be within the protection scope determined by the claims.

Claims

1. A method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model, characterized in that, Includes the following steps: S1: Acquire medical images, extract and establish a coronary artery model, the cross-section of the aortic root, and the total volume of the myocardium; S2: Collateral vessels are generated upstream and downstream of each coronary artery in the coronary vessel model; S3: Treat all the coronary arteries and collateral vessels as main vessels, and obtain the location coordinates of the exit of each main vessel and the vessel radius; S4: Based on the position coordinates of each main blood vessel outlet, and by fitting the ellipsoid equation, construct the myocardial outer wall equation, and then combine it with the cross section where the aortic root is located to obtain the myocardial outer wall surface; S5: Based on the principle that the outer wall of the myocardium is similar to the inner wall of the myocardium, the inner wall of the myocardium is constructed according to the outer wall of the myocardium, and the volume enclosed by the outer wall of the myocardium, the inner wall of the myocardium, and the cross-section where the aortic root is located is equal to the total volume of the myocardium, thereby forming a myocardial model; S6: The internal layers of the myocardial model are interpolated using ellipsoidal surfaces, and a thickness is assigned to each layer; S7: Divide each layer of the myocardial model into meshes and obtain the point cloud file for each layer; S8: Randomly select point P in the outermost point cloud file of the myocardial model, pre-connect point P with the outlet of each main blood vessel, and select a segment of blood vessel from the pre-connection to generate a blood vessel as a microcirculatory blood vessel according to the principle of minimizing the total volume of the generated blood vessel. S9: Repeat step S8 until a microcirculatory vessel is generated at the outlet of each main blood vessel; S10: Randomly select point T in the point cloud file of the myocardial model in the current layer and outside the current layer, and pre-connect the m microcirculatory vessels closest to point T. For each pre-connected microcirculatory vessel, according to the principle that the total pressure drop of each branch under the same main vessel outlet is equal and the total volume of the microcirculatory vessel is minimized, select point K to connect point T and the upstream and downstream of the microcirculatory vessel respectively, and generate multiple microcirculatory vessels in a bifurcation pattern. Combine the area bifurcation power law rule to set the vessel radius of each newly generated microcirculatory vessel. Compare the total volume of all the pre-connected vascular trees and retain the pre-connection case with the smallest total volume of the vascular tree. The vascular tree includes coronary arteries, collateral vessels and microcirculatory vessels. S11: Repeat step S10 until the number of newly generated bifurcated microcirculatory vessels in the point cloud file of the myocardial model of this layer reaches the preset number of bifurcations. S12: Take the layer inside the current layer as the current layer, repeat step S11, and gradually advance to the innermost layer until the radius of all blood vessel outlets in the generated blood vessel tree is less than the preset blood vessel threshold. S13: Based on the vascular tree obtained in step S12, calculate the resistance value of each outlet of the main vascular system; In step S10, the radius of each newly generated microcirculatory vessel is specifically set according to the area bifurcation power law rule as follows: The generated bifurcated microcirculatory vessels include K-upper vessels, K-downper vessels, and KT vessels. The radius of the K-upper vessel is equal to the radius of the main vessel outlet. The radii of the K-downper vessel and the KT vessel are equal. The calculation expressions for the radii of the K-downper vessel and the KT vessel are as follows: In the formula, The radius of the KT vessel is given. The radius of the downstream vessel of K- is [missing information]. The radius of the upstream vessel of K is [value missing]. It follows the power law of bifurcation; The point K is selected based on the principle that the total pressure drop of each branch under the same main blood vessel outlet is equal and the total volume of the microcirculation blood vessels is minimized. Specifically: Based on the principle that the total pressure drop of each branch under the same main blood vessel outlet is equal, the selected point K is specified to have the same length and cross-sectional area as the upstream and downstream blood vessels connected in the microcirculation blood vessels; based on the principle of minimizing the total volume of the microcirculation blood vessels, the selected point K is made to satisfy the condition that the total volume of the upstream and downstream blood vessels connected to point T in the microcirculation blood vessels is minimized. Step S2 is as follows: The number of additional collateral vessels and the vessel radius of each collateral vessel and the corresponding bifurcation power law are determined based on the upstream and downstream vessel radii of each coronary artery in the coronary vessel model. The additional collateral vessels are evenly distributed upstream and downstream of the corresponding coronary artery. The relationship between the increased number of collateral vessels, the radius of each collateral vessel, and the corresponding bifurcation power law is as follows: In the formula, The radius of the upstream vessel of the coronary artery. The radius of the downstream vessel of the coronary artery. For bifurcation power law, The number of collateral vessels, This represents the radius of the collateral vessel.

2. The method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model according to claim 1, characterized in that, In step S6, the thickness of each layer is assigned in a linear manner from the inside out.

3. The method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model according to claim 1, characterized in that, The method for obtaining microcirculatory vascular resistance at the end of the coronary artery further includes: obtaining the region of the cardiac cavity through the medical image; in the pre-connection process in steps S8 and S10, if the pre-connected blood vessel passes through the region of the cardiac cavity, the pre-connection is discarded. If, in step S10, the radius of the generated microcirculatory blood vessel is less than half of the blood vessel threshold, then the pre-connection with the corresponding microcirculatory blood vessel is discarded.

4. The method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model according to claim 1, characterized in that, In step S13, the calculation of the resistance value of each outlet of the main blood vessel specifically involves: calculating the resistance of each microcirculatory blood vessel based on Poiseuille's theorem, and then calculating the resistance of each blood vessel outlet in the vascular tree according to the series-parallel connection rule. The resistance is equivalent to electrical resistance, and the calculation expression for the resistance of each microcirculatory blood vessel is as follows: In the formula, For resistance, For blood viscosity, The length of the blood vessel. This represents the cross-sectional area of ​​the blood vessel.

5. The method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model according to claim 1, characterized in that, In step S13, the calculation of the resistance value of each outlet of the main blood vessel specifically involves: By calculating the capacitance and / or inductance of each blood vessel, the resistance of each blood vessel outlet in the vascular tree is determined. The expression for calculating the capacitance of the blood vessel is as follows: In the formula, For capacitors, This represents the cross-sectional area of ​​the blood vessel. The length of the blood vessel. Blood density, This refers to the pulse wave velocity. The expression for calculating the inductance of the blood vessel is: In the formula, It is an inductor.

6. The method for obtaining coronary microcirculation vascular resistance based on a layered myocardial model according to claim 1, characterized in that, The resistance of each blood vessel outlet in the vascular tree obtained in step S13 is used to set the outlet boundary conditions of the three-dimensional CFD model of the vascular tree.

7. A system for acquiring coronary microcirculation vascular resistance based on a layered myocardial model, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor calling the computer program to perform the steps of the method as described in any one of claims 1 to 6.

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