4D-Flow-CFD simulation model construction method and system for quantitatively evaluating cirrhosis portal vein hydrodynamics

Abstract

The invention discloses a 4D-Flow-CFD simulation model construction method and system for quantitative evaluation of cirrhosis portal vein hydrodynamics, and belongs to the technical field of medical image processing, the construction method comprises the following steps: step 1, placing a patient on a scanner, and sequentially performing structural image and 4D-Flow MRI (four-dimensional blood flow magnetic resonance) scanning; 2, integrating the 4D-Flow MRI and CFD (computational fluid dynamics) technology, performing post-processing on a 4D-Flow MRI image by adopting Circle software, and screening out hemodynamic characteristic parameters capable of representing the liver cirrhosis process; and 3, constructing a liver portal vein system finite element model by using the screened haemodynamic characteristic parameters so as to establish a quantitative evaluation model of portal vein haemodynamics of the patients with cirrhosis, so that a new haemodynamic detection method is explored for clinical systematic evaluation of cirrhosis, and a new thought is provided for accurate evaluation of cirrhosis.

Description

Technical Field

[0001] The present invention belongs to the technical field of image processing, and in particular relates to a 4D-Flow-CFD simulation model construction method and system for quantitatively evaluating portal vein flow dynamics in cirrhosis. Background Art

[0002] Cirrhosis is characterized by decreased liver function and portal hypertension. In the later stage, serious complications such as ascites and upper gastrointestinal bleeding will occur, which seriously endangers people's lives and health. In the early stage of cirrhosis, when there are no significant abnormalities in routine imaging examinations or even biochemical examinations, the hemodynamics of the liver has changed. And portal vein hemodynamics is an important prognostic indicator of chronic liver disease. Therefore, early identification of the presence of portal hypertension and accurate quantification of the severity of portal hypertension are of great guiding significance for the standardized treatment of cirrhosis.

[0003] Currently, the most reliable method for measuring portal vein hemodynamic parameters is percutaneous transhepatic portal vein catheterization and pressure measurement, but its invasiveness limits its widespread clinical application; ultrasound is currently the most commonly used technology for evaluating portal vein blood flow, but it depends on the operator's skills and is easily affected by various factors (such as gastrointestinal gas, ascites, etc.), and its accuracy is controversial; and CT portal vein angiography has the disadvantages of using iodine contrast agents, radiation damage, and inability to quantitatively evaluate portal vein blood flow status. Therefore, it is of great clinical significance to explore methods for early, non-invasive, and comprehensive evaluation of portal vein hemodynamic changes. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a 4D-Flow-CFD simulation model construction method and system for quantitatively evaluating the portal vein flow dynamics of cirrhosis. By integrating 4D-Flow MRI and CFD technology, a quantitative evaluation model of portal vein hemodynamics in patients with cirrhosis is constructed, and new hemodynamic detection methods are explored for the systematic evaluation of clinical cirrhosis, thereby providing new ideas for the accurate evaluation of cirrhosis.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for constructing a 4D-Flow-CFD simulation model for quantitatively evaluating portal vein flow dynamics in cirrhosis, the method comprising the following steps:

[0007] Step 1: Place the patient on the scanner and perform structural imaging and 4D-FlowMRI scans of the portal vein in sequence;

[0008] Step 2: Post-process the 4D-Flow MRI images to screen out the hemodynamic characteristic parameters that can characterize the progression of liver cirrhosis;

[0009] Step 3: Use the screened hemodynamic characteristic parameters to construct a finite element model of the liver portal vein system.

[0010] In some embodiments, in step 2, Circle software is used to perform post-processing analysis on the 4D-Flow MRI image to measure the hemodynamic parameters of the main portal vein (MPV), the left branch of the portal vein, the right branch of the portal vein, the superior mesenteric vein (SMV) and the splenic vein (SV) in the vascular cavity plane. The measurement point is selected 2 cm away from the confluence of the superior mesenteric vein (SMV) and the splenic vein (SV). The measurement plane is perpendicular to the long axis of the blood vessel, and the hemodynamic parameter values ​​are recorded.

[0011] In some embodiments, blood flow parameters include blood flow, peak flow velocity, wall shear, and portal vein pressure.

[0012] In some embodiments, the specific implementation process of step 3 includes:

[0013] Step 301: importing the structural image obtained in step 1 into Mimics software, using image segmentation technology to set a gray value threshold that matches the gray value of the image, thereby segmenting the liver portal vein system area, establishing a three-dimensional model, and exporting it to STL format; importing the three-dimensional model in STL format into Geomagic Studio software, performing smoothing and integrity processing on the three-dimensional model in STL format, converting it into a CAD object, and exporting it to a STEP format file;

[0014] Step 302: Import the three-dimensional model in STEP format into Ansys software, use the SpaceClaim module to cut the blood flow inlet and outlet of the liver portal vein, and after the cutting is completed, use the FLUENT Meshing module to set the parameters in CFD Surface Control according to the diameter of the liver portal vein, view the three-dimensional model in the Outline View interface, right-click the model to generate a mesh and a fluid domain, perform tetrahedral unstructured meshing on the fluid domain, perform layered processing on the boundary, and perform hexahedral structured meshing on the structural part;

[0015] Step 303: Using the FLUENT Solution module, select Models-Viscous-Laminar, Materials-Fluid, Boundary Conditions-Inlet / Outlet / Wall in the left menu bar, and use the portal vein pressure obtained by 4D-Flow MRI to define the inlet flow rate, outlet pressure, and fluid-solid coupling surface boundary conditions of CFD, and define the material properties of the fluid and structure parts;

[0016] Step 304: Use the time-step iteration method to perform fluid-solid coupling calculations. Set the time step according to the blood pressure pulsation parameters. Transfer the flow field pressure, flow velocity and interface displacement through the fluid-solid coupling surface. Repeat the iteration until the solution of the fluid control equation tends to be stable. Draw a cloud map in the Results option of the FLUENT Solution module to visualize the results of the 4D-Flow-CFD simulation.

[0017] In a second aspect, the present invention provides a 4D-Flow-CFD simulation model construction system for quantitatively evaluating portal vein flow dynamics in cirrhosis, comprising the following steps:

[0018] The above method is used to implement the system, which includes:

[0019] In the acquisition module, the patient is placed on the scanner and the portal vein is scanned sequentially for structural imaging and 4D-Flow MRI;

[0020] The processing module performs post-processing on the 4D-Flow MRI images and selects the hemodynamic characteristic parameters that can characterize the progression of liver cirrhosis;

[0021] The model building module uses the screened hemodynamic characteristic parameters to construct a finite element model of the liver portal vein system.

[0022] In a third aspect, the present invention further provides an electronic device, including a processor and a memory, wherein the memory stores computer instructions, and the processor is used to execute the computer instructions stored in the memory to implement the steps of the above-mentioned method.

[0023] In a fourth aspect, the present invention further provides a computer-readable storage medium storing computer instructions, wherein the computer instructions are used to execute the steps of the method as described above.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention integrates 4D-Flow MRI and CFD technology to construct a quantitative evaluation model for portal vein hemodynamics in patients with cirrhosis, which not only makes up for the shortcomings of 4D-Flow MRI technology, but also expands the application of CFD technology in patients with cirrhosis under complex blood flow background conditions, and studies the subtle changes in portal vein blood flow status during the occurrence and development of cirrhosis from a mechanical perspective. It has important clinical significance for understanding the hemodynamic mechanism of cirrhosis, explores new hemodynamic detection methods for the systematic evaluation of clinical cirrhosis, and provides new ideas for the accurate evaluation of cirrhosis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the technical route of the present invention.

[0027] Figure 2 It is a measurement method of 4D-Flow MRI; among them, Mainportal vein (MPV) is the main trunk of the portal vein; Splenic vein (SV) is the splenic vein; Superiormesenteric vein (SMV) is the superior mesenteric vein.

[0028] Figure 3 It is the three-dimensional geometric model of the portal vein.

[0029] Figure 4 This is the meshing result of the three-dimensional geometric model of the portal vein.

[0030] Figure 5 This is the hemodynamic distribution map 1.

[0031] Figure 6 This is the hemodynamic distribution map 2. DETAILED DESCRIPTION

[0032] In the description of the present invention, it should be noted that, if the specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0033] The present invention is further described below in conjunction with specific embodiments.

[0034] 80% of the blood supply to the liver comes from the portal vein. 4D-Flow MRI can simultaneously obtain the hemodynamic data of several blood vessels and retrospectively evaluate the blood flow velocity in the entire field of view. Studies have shown that 4D-Flow MRI can distinguish the differences in portal vein blood flow between healthy subjects and patients with cirrhosis, predict the prevalence and severity of cirrhosis and portal hypertension, as well as the risk of rupture of high-risk esophageal varicose veins and preoperative planning and follow-up studies for liver surgery and interventional treatment. Our previous study also found that 4D-Flow MRI blood flow imaging can more objectively reflect the changes in portal vein hemodynamics in patients with cirrhosis, and the blood flow (FR) and diameter of the portal vein trunk and splenic vein can be used as characteristic parameters for diagnosing cirrhotic varicose veins (AUC = 0.83). Therefore, 4D-Flow MRI is expected to become a valuable non-invasive examination technology for evaluating portal vein hemodynamics.

[0035] Cirrhosis is a progressive chronic liver disease caused by multiple etiologies, characterized by diffuse hepatocyte necrosis, abnormal hepatocyte regeneration, angiogenesis, massive proliferation of fibrous tissue, and pseudolobule formation. This leads to complex and diverse portal vein blood flow. First, the obstruction of portal vein blood flow into the liver causes increased portal vein pressure. There is also a debate about "backward blood flow" and "forward blood flow". However, 4D-Flow MRI requires a large range of data acquisition and three-dimensional velocity encoding, so the acquisition time is relatively long, and it is easily affected by noise and artifacts, resulting in a decrease in image quality. At the same time, due to the large scanning coverage, its spatial resolution is limited, and there is distortion in the hemodynamic analysis of small blood vessels. Our previous studies have also found that an important limitation of 4D-Flow MRI imaging technology is the lack of temporal and spatial resolution. At the same time, in order to ensure the accuracy of 4D-Flow MRI parameters, appropriate velocity encoding is also required. However, there is currently a lack of a unified velocity encoding standard. Inappropriate encoding may cause velocity aliasing, resulting in deviations in measurement results. Therefore, there are still certain limitations in using a single 4D-Flow MRI technique to study portal vein hemodynamics.

[0036] CFD is an interdisciplinary subject between mathematics, fluid mechanics and computers. It mainly uses computers and numerical methods to solve the governing equations of fluid mechanics and simulate and analyze fluid mechanics problems. With the development of computer technology, vascular morphology has gradually been characterized, and the research on solving mechanical problems through computer analysis has gradually increased, especially for complex blood vessels and bifurcated blood vessels. For example: evaluate the hemodynamic changes after occlusion of multiple intracranial aneurysms, understand the occurrence, growth and rupture of cerebral aneurysms, predict the hemodynamic characteristic parameters of unruptured cerebellar aneurysm growth, and evaluate intracranial atherosclerotic stenosis. At the same time, it also shows good application prospects in the treatment of chronic obstructive pulmonary disease, establishing left atrial blood flow, simulating non-invasive posterior urethral pressure, and establishing personalized liver cancer radioembolization dose models. In the early stage, we used CFD for intracranial aneurysm hemodynamic simulation and found that CFD can construct high-resolution three-dimensional geometric models of blood vessels and aneurysms, and can perform comprehensive hemodynamic analysis of the tumor-bearing artery, assisting the clinical diagnosis and treatment of intracranial aneurysms.

[0037] In terms of portal vein applications, most current research is based on CFD simulations based on CT enhanced images, and the focus is mainly on the main trunk of the portal vein. However, changes in portal vein hemodynamics in cirrhosis may only appear in small branches in the early stages, while the main trunk may not change; at the same time, accurate assessment of the hemodynamics of small side branches is also required to predict the risk of complications of portal hypertension. Computational fluid dynamics based on 4D-Flow MRI (4D-Flow-CFD) uses the portal vein pressure and flow velocity measured by 4D-Flow MRI as the inlet flow velocity required to construct CFD, and uses MRI structural images to construct a complete vascular three-dimensional geometric pathway from the blood sinus to the portal vein, which is expected to systematically and comprehensively quantify the portal vein hemodynamic state.

[0038] Based on the above ideas, a 4D-Flow-CFD simulation model construction method for quantitatively evaluating the portal vein flow dynamics in cirrhosis was formed, such as Figure 1 As shown, the specific research contents are as follows:

[0039] 1. Volunteer recruitment

[0040] When the liver is diseased, its hemodynamic changes are mainly affected by blood flow resistance, blood flow, vascular wall hardening, vascular endothelial cell damage and other factors in the blood circulation. These changes can lead to reduced blood flow, reduced blood flow velocity, changes in blood flow patterns, vascular endothelial cell apoptosis and increased blood flow resistance, which in turn lead to liver function damage. Therefore, in order to understand this process, this study plans to recruit 120 volunteers, including 30 healthy volunteers and 90 volunteers with cirrhosis (according to the Child-Pugh classification, 30 volunteers in each level).

[0041] 2. Collection of laboratory indicators of volunteers and population baseline data

[0042] Laboratory data of volunteers were collected, including routine blood tests: WBC count, NEUT, Hb, PLT; liver function tests: ALT, AST, ALB, TBIL; coagulation function tests: PT, PTA, APTT.

[0043] Collection of demographic baseline data: record the volunteer's gender, age, height, marital history, life history, etc.

[0044] 3. Imaging examination of volunteers

[0045] The volunteers were placed on the SignaArchitect 3.0T scanner produced by GE and underwent structural imaging and 4D-Flow MRI scans.

[0046] 4. Image Processing

[0047] The Circle software produced by Circle Cardiovascular Ltd. of Canada was used for post-processing analysis of 4D-Flow MRI images to measure the main portal vein blood flow parameters (FV, FR blood flow, peak flow velocity, wall shear force) and portal vein pressure in the vascular lumen plane.

[0048] 5. Finite element model of liver portal vein system

[0049] Using MRI thin-layer data, the 4D-Flow MRI images were post-processed, and the three-dimensional visualization images of the portal vein and various hemodynamic parameters were deeply studied. The hemodynamic characteristic parameters that can characterize the process of cirrhosis were screened out, and a finite element model of the liver portal vein system was accurately constructed. The changes in portal vein hemodynamic parameters in cirrhosis were analyzed based on the computational fluid dynamics method, and the relevant statistical analysis of the morphological parameters and hemodynamic parameters of the liver was performed. The biomechanical mechanism of the liver was explored, and the changing laws of hemodynamics in the process of cirrhosis were explained from a mechanical perspective.

[0050] The specific operations are as follows:

[0051] 5.14D-Flow MRI hemodynamic parameter acquisition

[0052] The Circle software produced by Circle Cardiovascular Ltd. of Canada was used for post-processing analysis to measure the blood flow parameters (blood flow, peak flow velocity, wall shear force, portal vein pressure) of the portal vein trunk (MPV), left portal vein branch, right portal vein branch, superior mesenteric vein (SMV), splenic vein (SV) and other parts in the vascular cavity plane. The measurement point was selected to be about 2 cm away from the confluence of SMV and SV, and the measurement plane was perpendicular to the long axis of the blood vessel (as shown below). Figure 2 ) and record the vascular values.

[0053] 5.2CFD Construction

[0054] Using MRI thin-layer data, the geometric structure of the liver portal vein system was reconstructed in three dimensions and its finite element model was constructed. The portal vein pressure and flow velocity obtained by 4D-Flow MRI were set as the inlet flow velocity of CFD, and Ansys CFX was used to solve the fluid area based on the idea of ​​finite volume method, and Ansys Fluent was used to solve the structure part based on the fluid-solid coupling method. The specific implementation process is as follows:

[0055] (1) Importing the structural image obtained above into Mimics software, using image segmentation technology to set a gray value threshold that matches the gray value of the image, thereby segmenting the liver portal vein system area, establishing a three-dimensional model, and exporting it to STL format; importing the three-dimensional model in STL format into Geomagic Studio software, selecting the options of Delete Spikes, Mesh Doctor, Precise Surface, Surface Automation, and Fit Surface in the software menu bar in turn, smoothing and integrity processing the three-dimensional model in STL format, converting it into a CAD object, and exporting it to a STEP format file;

[0056] (2) Import the 3D model in STEP format into Ansys software. Use the SpaceClaim module and select Sketch-Circle, Design, and Sketch Mode in the menu bar in turn to cut the blood flow inlet and outlet of the liver portal vein. After cutting, click End Sketch Drawing and Combine in the menu bar, and finally click Esc to exit. Use the FLUENT Meshing module to set the parameters in CFD Surface Control according to the diameter of the liver portal vein. View the 3D model in the Outline View interface, right-click the model to generate the mesh and fluid domain, perform tetrahedral unstructured meshing on the fluid domain, perform layered processing on the boundary, and perform hexahedral structured meshing on the structural part.

[0057] (3) Using the FLUENT Solution module, select Models-Viscous-Laminar, Materials-Fluid, Boundary Conditions-Inlet / Outlet / Wall in the left menu bar, and use the portal vein pressure obtained by 4D-Flow MRI to define the CFD inlet flow rate, outlet pressure, and fluid-solid coupling surface boundary conditions, and define the material properties of the fluid and structure parts;

[0058] (4) The time-step iteration method is used to perform fluid-solid coupling calculations. The time step is set according to the blood pressure pulsation parameters. The flow field pressure, flow velocity, and interface displacement are transmitted through the fluid-solid coupling surface. The iteration is repeated until the solution of the fluid control equation decreases and tends to be stable. A cloud map is drawn in the Results option of the FLUENT Solution module to visualize the results of the 4D-Flow-CFD simulation.

[0059] Specifically, the parametric modeling software Proe was used to process the liver 3D model to generate a 3D geometric model of the portal vein with wall thickness ( Figure 3 After the blood vessel model is imported into Ansys, it is filled and processed to generate the fluid domain. The fluid domain is divided into tetrahedral unstructured grids, the boundaries are layered, and the structural part is divided into hexahedral structured grids ( Figure 4).

[0060] The portal vein pressure measured by 4D-Flow MRI is used to define boundary conditions such as inlet flow velocity, outlet pressure, and fluid-solid coupling surface, and to define the material properties of the fluid and structural parts.

[0061] The time-step iteration method is used for fluid-solid coupling calculation. The appropriate time step is set according to the blood pressure pulsation parameters. The flow field pressure, flow velocity and interface displacement are transmitted through the fluid-solid coupling surface. The cycle is repeated until the convergence condition is met, and finally the blood flow mechanics distribution map is obtained ( Figure 5 , Figure 6 ).

[0062] This application starts from the portal vein hemodynamics that affect the liver state, collects and screens the hemodynamic characteristic parameters that characterize the progression of cirrhosis, analyzes the influence of hemodynamic parameters on the occurrence, development, and outcome of cirrhosis, studies the changing patterns of portal vein blood flow in the progression of cirrhosis, and provides comprehensive hemodynamic information on cirrhosis. It has important clinical significance for understanding the hemodynamic mechanism of cirrhosis. The research results will have a profound impact on the research field of cirrhosis, provide a scientific basis and new strategies for the diagnosis and treatment of cirrhosis and related liver diseases, and have significant social value and economic benefits.

Claims

1. A 4D-Flow-CFD simulation model construction method for quantitatively evaluating portal vein flow dynamics in cirrhosis, characterized in that: The construction method includes the following steps: Step 1: Place the patient on the scanner and perform structural imaging and 4D-FlowMRI scans of the portal vein in sequence; Step 2: Post-process the 4D-Flow MRI images to screen out the hemodynamic characteristic parameters that can characterize the progression of liver cirrhosis; Step 3: Use the screened hemodynamic characteristic parameters to construct a finite element model of the liver portal vein system.

2. A 4D-Flow-CFD simulation model construction method for quantitatively evaluating portal vein flow dynamics in cirrhosis according to claim 1, characterized in that: In step 2, the Circle software was used to post-process and analyze the 4D-Flow MRI images, and the hemodynamic parameters of the portal vein trunk, left portal vein branch, right portal vein branch, superior mesenteric vein, and splenic vein in the vascular cavity plane were measured. The measurement point was selected 2 cm from the confluence of the superior mesenteric vein and splenic vein. The measurement plane was perpendicular to the long axis of the blood vessel, and the hemodynamic parameter values ​​were recorded.

3. A 4D-Flow-CFD simulation model construction method for quantitatively evaluating portal vein flow dynamics in cirrhosis according to claim 2, characterized in that: Hemodynamic parameters included blood flow, peak flow velocity, wall shear force, and portal vein pressure.

4. A 4D-Flow-CFD simulation model construction method for quantitatively evaluating portal vein flow dynamics in cirrhosis according to claim 3, characterized in that: The specific implementation process of step 3 includes: Step 301: importing the structural image obtained in step 1 into Mimics software, using image segmentation technology to set a gray value threshold that matches the gray value of the image, thereby segmenting the liver portal vein system area, establishing a three-dimensional model, and exporting it to STL format; importing the three-dimensional model in STL format into Geomagic Studio software, performing smoothing and integrity processing on the three-dimensional model in STL format, converting it into a CAD object, and exporting it to a STEP format file; Step 302: Import the three-dimensional model in STEP format into Ansys software, use the SpaceClaim module to cut the blood flow inlet and outlet of the liver portal vein, and after the cutting is completed, use the FLUENT Meshing module to set the parameters in CFD Surface Control according to the diameter of the liver portal vein, view the three-dimensional model in the Outline View interface, right-click the model to generate a mesh and a fluid domain, perform tetrahedral unstructured meshing on the fluid domain, perform layered processing on the boundary, and perform hexahedral structured meshing on the structural part; Step 303: Using the FLUENT Solution module, select Models-Viscous-Laminar, Materials-Fluid, Boundary Conditions-Inlet / Outlet / Wall in the left menu bar, and use the portal vein pressure obtained by 4D-Flow MRI to define the inlet flow rate, outlet pressure, and fluid-solid coupling surface boundary conditions of CFD, and define the material properties of the fluid and structure parts; Step 304: Use the time-step iteration method to perform fluid-solid coupling calculations. Set the time step according to the blood pressure pulsation parameters. Transfer the flow field pressure, flow velocity and interface displacement through the fluid-solid coupling surface. Repeat the iteration until the solution of the fluid control equation tends to be stable. Draw a cloud map in the Results option of the FLUENT Solution module to visualize the results of the 4D-Flow-CFD simulation.

5. A 4D-Flow-CFD simulation model construction system for quantitatively evaluating portal vein flow dynamics in cirrhosis, characterized in that: The method according to any one of claims 1 to 4 is implemented, and the system comprises: In the acquisition module, the patient is placed on the scanner and the portal vein is scanned sequentially for structural imaging and 4D-Flow MRI; The processing module performs post-processing on the 4D-Flow MRI images and selects the hemodynamic characteristic parameters that can characterize the progression of liver cirrhosis; The model building module uses the screened hemodynamic characteristic parameters to construct a finite element model of the liver portal vein system.

6. An electronic device comprising a processor and a memory, characterized in that: The memory stores computer instructions, and the processor is used to execute the computer instructions stored in the memory to implement the steps of the method as described in any one of claims 1 to 4.

7. A computer-readable storage medium storing computer instructions, characterized in that: The computer instructions are used to execute the steps of the method as claimed in any one of claims 1 to 4.

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