Coronary artery virtual stent implantation method and system based on hemodynamic analysisTechnical Field
The invention relates to a coronary artery virtual stent implantation method and system based on hemodynamic analysis.
Background
The drug therapy, the operation therapy and the catheter minimally invasive interventional operation therapy are three most commonly used methods for treating coronary heart disease at present. The minimally invasive interventional therapy is a special method for diagnosing and treating coronary heart disease by using a special catheter and an instrument, and inserting the catheter and the instrument into a human body through percutaneous puncture or a certain original channel of the human body so as to reach a diseased part. Percutaneous Transluminal Coronary Angioplasty (PTCA) is a minimally invasive interventional therapy for coronary heart disease that is widely used in clinical practice. In the course of PTCA surgery, the support material of metal or other material in the shape of a mesh tube, which is used to be implanted in a coronary vessel of a human body and which serves to support and prop up the vessel, is a coronary stent. Stents are typically mounted on a balloon catheter device and are delivered to the stenotic lesion through the balloon catheter device under X-ray radiographic monitoring; then, inflating and expanding the balloon at the tail end of the balloon catheter, and then expanding the stent to force the vessel cavity at the narrow part to be open, so that blood can normally pass through the vessel; finally, the saccule device is withdrawn, and the blood vessel stent is permanently fixed at the lesion part, thereby achieving the purposes of supporting the narrow blood vessel and keeping the blood flow unobstructed.
In the PTCA intravascular stent placement operation, the selection of the size and the placement mode of the stent and the accurate positioning of the stent are critical to the success of the operation. The current clinical diagnostic method is to estimate the lesion degree of the blood vessel and the model of the needed stent by using some two-dimensional analysis techniques based on X-ray Coronary Angiography (CAG) or CT coronary angiography (CTA) images. However, the spatial information provided by CAG or CTA images is very limited and does not truly reflect the actual condition of the vessel and its lesions. Moreover, the measurement results are affected by subjective factors, which makes it difficult to accurately estimate the type of the stent used.
In light of the above deficiencies and the practical requirements of clinical applications, people are beginning to explore and develop virtual stent implantation systems for planning before artery stenting operation. Such as philips INTEGRIS 3D-RA workstation, build a patient-specific vessel model by automatic and semi-automatic image segmentation tools in combination with mesh generation tools, and automatically extract vessel lumen centerlines on the three-dimensional image model. A virtual stent is then placed along the lumen centerline and the length and diameter of the stent are interactively adjusted for surgical planning, such as simulated stent placement, simulated blood flow procedures, and the like. The method can visually display the effect of placing the stent at the narrow part of the vascular cavity in the stent implantation operation, and the stent can be repeatedly replaced until the model is proper. But the defects are that the calculation of the degree of the stenosis of the blood vessel cannot be automatically carried out, the lesion cannot be automatically identified and a stent strategy is generated, the influence of stent implantation on the fractional flow reserve cannot be predicted too much depending on the experience of a doctor, and the condition of improving the patient by the operation cannot be objectively evaluated.
Among them, Fractional Flow Reserve (FFR) is a "gold standard" for clinical judgment of myocardial ischemia, and is an important technique for diagnosing physiological functions of coronary artery. FFR determines whether a stenosis induces ischemia by measuring the ratio of the pressure at the distal end to the pressure at the proximal end of the stenosis in the maximal hyperemic state in response to the restriction of the maximum blood flow by the stenosis. A large number of clinical trials provide evidence-based medical evidence to date, and the FFR can be used for evaluating the functional significance of the stenosis, and especially has important guiding significance for selecting a treatment scheme for critical stenosis. Measurement of FFR is invasive, however, and researchers have begun to perform mechanical analysis and studies of stented vessels using finite element analysis to quantitatively assess stent improvement in blood flow. The specific method is to perform Computational Fluid Dynamics (CFD) analysis based on a three-dimensional geometric model of the blood vessel. CFD is a computer program-based method of solving fluid mechanics equations, and CFD calculations require knowledge of the shape of the flow region and the mechanical parameters of the fluid itself. The three-dimensional shape of the blood vessel can be reconstructed by CT and MRI technologies, the blood vessel and the surrounding tissues are separated according to the gray levels of CT and MRI images, then the grid is continuously divided, and the grid is formed by combining tetrahedrons or hexahedrons and is calculated. The whole CFD calculation is based on solving partial differential equations, and the required calculation accuracy can be achieved by adjusting the spatial resolution and the time resolution.
Disclosure of Invention
The invention aims to provide a coronary artery virtual stent implantation method and system based on hemodynamic analysis, which can automatically complete the calculation of the stenosis degree of a blood vessel, generate a stent implantation strategy, quantitatively evaluate the implantation effect of a virtual stent, reduce the dependence on personal experience, improve the decision-making efficiency of doctors and reduce the decision risk of the doctors.
The invention relates to a coronary artery virtual stent implantation method based on hemodynamic analysis, which comprises the following steps:
reading coronary artery CTA image data of a patient, identifying calcified plaque, establishing a coronary artery blood vessel three-dimensional image model, removing the calcified plaque and recording the position of the calcified plaque;
receiving the physiological parameters of the patient, setting the boundary conditions of CFD, performing CFD calculation to obtain the stable blood flow speed and pressure at each part of the coronary artery, and obtaining the FFR at each part of the coronary artery according to the ratio of the blood flow pressure at each part of the coronary artery to the mean pressure of the aorta;
according to the three-dimensional blood vessel form, the calcified plaque characteristics and the FFR value of each part of the coronary blood vessel, carrying out lesion identification on the coronary blood vessel three-dimensional image model;
generating a virtual stent implantation scheme according to the identified lesion, a stent specification database and a preset virtual stent implantation strategy, and generating a new blood vessel three-dimensional geometric model after virtual stent implantation;
and under the new three-dimensional geometric model of the blood vessel, performing CFD calculation again to obtain a new FFR value, and outputting an optimal virtual stent implantation scheme according to a preset virtual stent implantation scheme selection standard.
According to one embodiment of the invention, the method for identifying the lesion on the blood vessel three-dimensional image model comprises the following steps:
calculating the coronary stenosis degree G
G＝1－DX/DZ，
In the formula DXDiameter of the vessel at the stenosis DZNormal vessel diameter;
or G-1-SX/SZ
In the formula SXThe area of the blood vessel in the stenosis SZNormal blood vessel area;
finding out all points which accord with the coronary artery stenosis degree of more than 50 percent, combining the points into different stenosis sections, and combining adjacent stenosis sections for a single section of blood vessel according to a preset distance threshold value; the bifurcations are divided into seven types according to the Medina classification method according to the stenosis degree and the position;
the lesions on coronary vessel trees become one of two types:
(a) lesions on a single segment of a vessel (starting location, ending location);
(b) bifurcation lesions (starting point, first bifurcation termination point, second bifurcation termination point);
and removing the lesion with the FFR larger than 0.8 according to the FFR after the lesion, wherein the rest lesion needs to be implanted with a stent.
According to an embodiment of the present invention, the diameter of the stenosis is obtained by conversion of a cross-sectional area: the stenosis diameter is 4 cross-sectional area/circumference and the normal vessel diameter is obtained by fitting a curve of the diameter of the entire vessel.
According to one embodiment of the present invention, the data stored in the stent specification database includes the stent specification models, the fully expanded diameter and the length of the stent of each manufacturer; the stent implantation strategy is as follows:
the bifurcation lesion adopts a bracket strategy aiming at the bifurcation lesion and arranged by a Chen forest;
if the lesion needing to be treated contains calcified plaque on the main branch proximal segment, and the distance between the calcified plaque and the side branch is less than or equal to 10mm on the side close to the side branch, the side branch also needs to be protected by a stent, namely the side branch also needs to be implanted with the stent to prevent the main branch from being implanted with the stent and crushing the plaque, and the broken plaque blocks the side branch downwards along with blood flow;
the fully-opened size of the stent is not less than the average diameter of the normal blood vessel fitted by the lesion section and not more than the product of the average diameter of the normal blood vessel fitted by the lesion section and a preset threshold value.
According to one embodiment of the invention, the preset selection criteria of the virtual stent implantation scheme are that FFR is more than 0.8 after the virtual stent implantation and the number of implanted stents is minimum.
The invention relates to a coronary artery virtual stent implantation system based on hemodynamic analysis, which comprises at least one computer system, wherein the at least one computer system is configured to:
reading coronary artery CTA image data of a patient, identifying calcified plaque, establishing a coronary artery blood vessel three-dimensional image model, removing the calcified plaque and recording the position of the calcified plaque;
receiving the physiological parameters of the patient, setting the boundary conditions of CFD, performing CFD calculation to obtain the stable speed and pressure of each part of the coronary artery, and obtaining the FFR of each part of the coronary artery according to the ratio of the blood pressure of each part of the coronary artery to the mean pressure of the aorta;
according to the three-dimensional blood vessel form, the calcified plaque characteristics and the FFR value of each part of the coronary blood vessel, carrying out lesion identification on the coronary blood vessel three-dimensional image model;
generating a virtual stent implantation scheme according to the identified lesion, a stent specification database and a preset virtual stent implantation strategy, and performing virtual stent implantation to generate a new blood vessel three-dimensional geometric model;
and under the new three-dimensional geometric model of the blood vessel, performing CFD calculation again to obtain a new FFR value, and outputting an optimal virtual stent implantation scheme according to a preset virtual stent implantation scheme selection standard.
According to one embodiment of the invention, the method for identifying the lesion on the coronary vessel three-dimensional image model comprises the following steps:
calculating the coronary stenosis degree G
G＝1－DX/DZ，
In the formula DXDiameter of the vessel at the stenosis DZNormal vessel diameter;
or G-1-SX/SZ
In the formula SXThe area of the blood vessel in the stenosis SZNormal blood vessel area;
finding out all points which accord with the coronary artery stenosis degree of more than 50 percent, combining the points into different stenosis sections, and combining adjacent stenosis sections for a single section of blood vessel according to a preset distance threshold value; the bifurcations are divided into seven types according to the Medina classification method according to the stenosis degree and the position;
all the diseases on the coronary vessel tree are changed into one of the following two diseases:
(a) lesions on a single segment of a vessel (starting location, ending location);
(b) bifurcation lesions (starting point, first bifurcation termination point, second bifurcation termination point);
and removing the lesion with the FFR larger than 0.8 according to the FFR after the lesion, wherein the rest lesion needs to be implanted with a stent.
According to one embodiment of the invention, the diameter D of the vessel at the stenosisXThe cross-sectional area S is converted into:
DX＝4*S/L
wherein S is the cross-sectional area and L is the perimeter;
normal vessel diameter is obtained by fitting a diameter curve of the entire vessel.
According to one embodiment of the present invention, the data stored in the stent specification database includes the stent specification models, the fully expanded diameter and the length of the stent of each manufacturer; the stent implantation strategy is as follows:
the bifurcation lesion adopts a bracket strategy aiming at the bifurcation lesion and arranged by a Chen forest;
if the lesion needing to be treated contains calcified plaque on the main branch proximal segment, and the distance between the calcified plaque and the side branch is less than or equal to 10mm on the side close to the side branch, the side branch also needs to be protected by a stent, namely the side branch also needs to be implanted with the stent to prevent the main branch from being implanted with the stent and crushing the plaque, and the broken plaque blocks the side branch downwards along with blood flow;
the fully-opened size of the stent is not less than the average diameter of the normal blood vessel fitted by the lesion section and not more than the product of the average diameter of the normal blood vessel fitted by the lesion section and a preset threshold value.
According to one embodiment of the invention, the preset selection criteria of the virtual stent implantation scheme are that FFR is more than 0.8 after the virtual stent implantation and the number of implanted stents is minimum.
The coronary artery virtual stent implantation method and system based on the hemodynamic analysis have the following beneficial effects:
(1) the invention can automatically calculate the stenosis degree, can avoid the problems of experience deviation and low efficiency caused by manual measurement in the prior art, and has very high processing efficiency. At present, a plurality of image post-processing software of CT equipment manufacturers can assist doctors to manually measure coronary stenosis degree, and the manual measurement is experienced in deviation and low in efficiency.
(2) The invention can automatically generate the stent implantation strategy, and can form a plurality of complete operation schemes including stent implantation alternative schemes before the stent implantation operation so as to improve the decision efficiency of doctors and reduce the risk brought by temporary decision in the operation.
(3) The coronary artery virtual stent implantation method can quantitatively evaluate the effect of the coronary artery virtual stent implantation scheme, can automatically recommend the optimal stent scheme, and reduces the decision risk of doctors depending on experience. Through quantifying coronary artery stenosis degree, the accurate presentation of pathological change position and scope, and the hemodynamic evaluation after the stent implantation, quantify the improvement effect of the stent implantation operation to the state of an illness to a certain extent, realized accurate operation scheme planning, reduce the risk of relying on artifical judgement.
The coronary artery virtual stent implantation method and system based on the hemodynamic analysis of the invention are further described in detail below with reference to the accompanying drawings.
Drawings
FIG. 1 is a flow chart of a coronary artery virtual stent implantation method based on hemodynamic analysis according to the present invention;
FIG. 2 is a graph of a vessel diameter fit in accordance with an embodiment of the present invention;
fig. 3 is a schematic diagram of Medina classification for bifurcation lesions;
FIG. 4 is a schematic view of a lesion containing calcified plaque;
fig. 5 is a diagram illustrating the effect of mesh filling on the original three-dimensional mesh after implantation of the virtual stent in an embodiment of the present invention.
Detailed Description
Referring to fig. 1, the coronary artery virtual stent implantation method based on the hemodynamic analysis of the invention comprises the following steps:
s1, reading in a DICOM image file of CT scanning of a patient, selecting seed points through a method of artificial assistance or automatic positioning of computer software, such as machine learning, and generating a three-dimensional image model of coronary vessels through an image growth algorithm, wherein a specific generation method can be seen in patent applications: application number 2015103631541 entitled coronary artery three-dimensional image segmentation method.
During image growth, according to the characteristic that the calcified plaque is high in brightness, plaque information is obtained by setting a threshold value, and the position information of the removed calcified plaque is removed from the three-dimensional image model of the coronary artery blood vessel of the patient and recorded, so that the three-dimensional model of coronary artery blood flow specific to the patient is obtained.
Then, through three-dimensional image processing software, the three-dimensional model of coronary blood flow is smoothed and gridded, for example, the model is divided into small tetrahedrons, a central line is generated, and the information of vessel bifurcation and diameter is obtained.
S2, receiving physiological parameters of a patient, setting boundary conditions of fluid calculation, obtaining stable blood flow speed and pressure at each part of a coronary artery, and obtaining the FFR at each part of the coronary artery according to the ratio of the blood flow pressure at each part of the coronary artery to the mean pressure of the aorta.
The boundary conditions are used to describe blood flow characteristics, including blood flow velocity, pressure, etc., at the boundaries of the coronary three-dimensional model anatomy. The boundary conditions vary due to the physiological condition of the patient, as the blood flow through the heart may vary due to the physiological condition of the patient. Since the fractional flow reserve FFR of a patient is measured under hyperemic physiological conditions and can also be induced pharmacologically, for example with adenosine, the boundary conditions calculated for the fluid should also be those under hyperemic conditions. The physiological parameters of the patient, such as heart rate, blood pressure, etc., which can be obtained are basically in the resting state of the patient, so that a patient physiological parameter model needs to be defined to simulate the change of the physiological parameters of the patient from the resting state to the hyperemic state.
The patient physiological parameter model may be obtained by prior medical knowledge or medical statistics. There is medical knowledge, such as the relationship of total blood flow to myocardial mass. Medical statistics can be derived from known parameters such as age, heart rate, weight, blood pressure, etc. by taking a sufficient sample size of patients and collecting their physiological parameters and establishing relationships between the physiological parameters by regression analysis to derive unknown parameters such as coronary inlet pressure.
After the boundary conditions are set, fluid mechanics calculation methods, such as Navier-Stokes equations, namely N-S equations, are called to perform fluid calculation, and the blood flow velocity and pressure of each grid on the blood vessel are obtained.
The N-S equation is shown in equation (1) and equation (2).
Formula (1) isThe N-S equation of Newtonian fluid can be compressed, and the formula (2) is a momentum conservation equation. Wherein,is the laplace operator, ρ is the fluid density, p is the pressure, u is the velocity of the fluid, F is the external force, μ depends on the properties of the fluid, called the viscosity coefficient. The velocity and pressure of the blood flow are numerically solved by variational and finite element methods. According to the principle, a three-dimensional blood vessel model is segmented, a fluid field of the blood vessel is converted into a space filled with a limited number of tetrahedrons, an N-S equation is numerically solved on each tetrahedron to obtain speed and pressure, the interaction between the tetrahedrons is considered, and stable blood flow speed and pressure at each position of the blood vessel are obtained through iterative calculation.
As defined for FFR, Pd/Pa, Pd: stenotic distal coronary mean pressure at maximum hyperemia, Pa: mean aortic pressure in the maximal hyperemic state. The fractional flow reserve FFR of the grid is obtained by the ratio of the blood pressure at the grid to the mean pressure of the aorta.
And S3, according to the three-dimensional blood vessel shape, the plaque characteristics and the FFR value of each part of the coronary blood vessel, carrying out lesion identification and classification on the coronary blood vessel three-dimensional image model.
Assessment of the degree of coronary stenosis is a prerequisite for performing stenting procedures. The degree of coronary stenosis can be defined by diameter or area, i.e. the degree of coronary stenosis G is calculated
G＝1－DX/DZ，
In the formula DXDiameter of the vessel at the stenosis DZNormal vessel diameter;
or G-1-SX/SZ
In the formula SXThe area of the blood vessel in the stenosis SZNormal blood vessel area;
on the basis of obtaining a coronary artery three-dimensional blood vessel model, a central line is obtained through calculation, and the area and the diameter of the coronary artery are calculated along the central line. Since the coronary vessel is not necessarily a regular cylinder, the diameter can be calculated by area conversion, and calculated by equivalent diameter, for example, 4 × cross-sectional area/circumference. In order to obtain the stenosis degree of a specific point on the central line of the blood vessel, the normal vessel diameter, i.e. the vessel diameter when the blood vessel is not stenosed, is obtained by fitting the diameter curve of the whole blood vessel, see fig. 2. The normal vessel fitting method may be to remove the abnormal points on the vessel first, because the plaque causes the vessel of the three-dimensional reconstruction to be too narrow or too wide, such as removing the points with the average diameter of 2 times or 1/2, and then to perform linear fitting to obtain the vessel diameter of the normal vessel.
The degree of stenosis at each point on the vessel can be measured as 1-vessel diameter/fitting to the normal vessel diameter, as in FIG. 2, 1-d 2/d 1. By finding and combining all points with a stenosis degree of more than 50% into different small segments. And the small narrow segments less than 2mm apart are merged into a large narrow segment according to a preset distance threshold, such as 2 mm.
The stenosis at the bifurcation is divided into seven types according to the internationally more popular Medina classification according to the degree and location of the stenosis, see fig. 3, i.e. the multiple lesions at the bifurcation can be merged into one large lesion according to the Medina classification.
Thus, all lesions on the coronary vessel tree will be one of two:
(a) lesions on a single segment vessel (starting position, ending position)
(b) Bifurcation lesion (first point of bifurcation, first point of bifurcation and second point of bifurcation)
Bifurcation lesions also need to be supplemented with calcified plaque information, and the location of calcified plaque will affect the posterior stent implantation strategy, concerning whether collateral needs protection.
And removing the lesions with FFR >0.8 according to the FFR value after lesion, which indicates that the lesions do not bring ischemia and do not need to be implanted with a stent. The remaining lesions require virtual stent implantation and evaluation.
And S4, generating a virtual stent implantation scheme according to the identified lesion, the stent specification database and a preset virtual stent implantation strategy, and generating a new blood vessel three-dimensional geometric model after virtual stent implantation.
The data stored in the support specification database comprises the support specification models, the fully-opened diameters and the lengths of the supports of all manufacturers. Aiming at each lesion, a virtual stent implantation strategy can be executed, the lesion on a single section of blood vessel is simpler, and the strategy of bifurcation lesion can be implanted by a single stent or double stents according to an instruction manual in the industry, such as a stent strategy aiming at bifurcation lesion in domestic aged forest arrangement. In addition, referring to fig. 4, if the bifurcation lesion to be treated contains calcified plaque 1, and the calcified plaque 1 is on the main proximal segment 2, and the distance a between the calcified plaque 1 and the side branch 3 is less than or equal to 10mm on the side close to the side branch 3, the side branch 3 also needs to be protected by a stent, i.e. the side branch 3 also needs to be implanted by the stent to prevent the main branch from being implanted with the stent, crushing the plaque, and blocking the side branch 3 with the blood flow. When stent matching is performed, the model is selected through the diameter, the diameter of the completely expanded stent is not less than the average diameter of the normal blood vessel fitted to the lesion section and not more than the product of the average diameter of the normal blood vessel fitted to the lesion section and a preset threshold, for example, the preset threshold is 1.1, and the diameter of the matched stent is less than the product of 1.1 times the average diameter of the normal blood vessel fitted to the lesion section. The number of stents is then selected by the length of the lesion. Multiple virtual stent implantation schemes are possible for a lesion.
And after the virtual stent implantation scheme is confirmed, performing virtual stent implantation. And (3) simulating the space form of the blood vessel after the stent is implanted and the stent is completely opened by adopting a computer system, and filling grids on the original three-dimensional grid, wherein the dark color part is the original blood vessel 4, and the light color part is the filling 5 after the virtual stent is implanted, referring to fig. 5.
After the virtual stent is implanted, a new blood flow three-dimensional geometric model is generated.
And S5, under the new blood vessel three-dimensional geometric model, carrying out fluid calculation again to obtain a new FFR value, wherein the selection criterion can be that the minimum stent number is less and the FFR is more than 0.8 after implantation according to a preset selection criterion. For example, in case of the first scheme, two stents are required, the FFR value after stent implantation is 0.95, in case of the second scheme, one stent is required, the FFR value after stent implantation is 0.9, and in accordance with the principle of minimum number of stents, the second scheme is the optimal scheme. And outputting the optimal scheme for reference of a clinician.
The stent strategy for bifurcation lesions in domestic Chenjilin organization is described in the book of Chenjilin's main edition < < interventional therapy for coronary bifurcation lesions > > published by "people health Press" in 2008/08.