CN104107039A - Noninvasive portal vein hemodynamic parameter measuring method - Google Patents

Abstract

The invention provides a noninvasive portal vein hemodynamic parameter measuring method which includes the steps of firstly, using a thin-section CT image to build a three-dimensional geometric model of a liver portal vein; secondly, using the finite element analyzing method of hydromechanics calculating software ANSYS to perform meshing on the geometric model and build a three-dimensional mathematic model; thirdly, calculating the hemodynamic parameter of the portal vein in an analog manner to obtain a speed and pressure distribution effect picture. The method is safe, noninvasive, simple to operate, visualized, quantized and high in accuracy, and the effective model is built for scientific researches and clinic services.

Description

A kind of non-invasive portal venous flow Determination of Kinetic Parameters method

Technical field

The invention belongs to physiology, pathophysiology and clinical medicine domain, be specifically related to a kind of assay method of physiological parameter, more specifically relate to the assay method of portal venous flow kinetic parameter.

Background technology

In current physiology, pathophysiology research and clinical medicine practise, still lack a kind of safe noinvasive, easy and simple to handle, intuitively quantize and the high evaluation methodology of portal vein hydromechanics and the pressure parameter detection technique of accuracy.Conventional detection means includes wound property (as: portal vein puncture in portal vein catheterization, the puncture of B ultrasonic Guided Percutaneous THPV, art) and non-invasive (as: color doppler ultrasonography, CT angiography, magnetic resonance angiography) two large classes.

there is wound property detection technique

1. portal vein catheterization: the method is to assess the classical way of portal venous pressure in clinical position, is considered to " goldstandard ".During operation, by Seldinger method, measure HVPG, with this, assess portal venous pressure, but in fact HVPG reaction be that sinus hepaticus is pressed, be not real portal venous pressure.In addition, the method must complete under X-ray examination guiding, and person under inspection must accept a large amount of rays; This technical operation difficulty is larger, has thrombosis, wear the complication such as the total vein of neck may by mistake.

The super Guided Percutaneous THPV of 2.B puncture: research shows, to have the measurement of wound property to compare safer with other for the method, and the incidence rate of complication is lower.Yet the method need to be carried out under local anesthesia, inevitably can be subject to the impact that anaesthetic disturbs and pneumoretroperitoneum pressure of flaccid muscles changes; In addition, person under inspection's portal venous pressure generally the rising risk that can cause puncturing strengthen.

3. portal vein puncture in art: in art, directly portal vein puncture pressure measuring is reflection portal venous pressure method comparatively reliably, acquired results directly, quantification, accuracy be high.The limitation of the method is: operation must be opened abdomen and carried out under general anesthesia, is vulnerable to the impact of anaesthetic and person under inspection's stress state, therefore may there is certain deviation with actual portal venous pressure.

non-invasive detection technique

1. color doppler ultrasonography: the method is comparatively conventional in clinical and scientific research, its measurement index comprises internal diameter, blood flow rate and the blood flow of a splenic vein, Hepatic artery and splenic artery pulsatility index, drag index, liver vessel exponential sum Hepatic artery buffer index etc.Yet the subjectivity of the method the data obtained is strong, in close relations with examiner's technical merit, be also subject to the factor impacts such as patient respiratory, position and build.Research shows, this detection method is at present still without the specificity parameter of evaluation portal venous pressure, and existing indirect indexes can not truly reflect patient's portal venous pressure.

2.CT angiography: as a kind of non-invasive inspection technology, CT angiography three-dimensional reconstruction image can make up the limitation, multiaxis of crosspiece bit scan to multi-angle observation pathological changes; In addition, cheap expense and easy operation are easily accepted it by patient.But its limitation is: CT angiography only can provide anatomic information, judge the situations such as hepatoportal form, degree of mobility and side Zhi Xunhuan, directly quantitatively evaluating hemodynamic parameter.

3. magnetic resonance angiography: the method manifests gradually in the advantage that detects portal system hemodynamics information.Magnetic resonance angiography not only can show gate Venous system side Zhi Xunhuan and spatial relationship, also can carry out quantitative analysis to flow velocity, flow.Yet every analytical technology of application still cannot quantize to draw pylic pressure index at present, its expensive diagnostic fees has also limited its clinical practice to a certain extent.

In sum, at present conventional portal system hemodynamics parameter detecting technology is subject to the impact of various interference factors, as: have traumatic, data do not quantize and it is large etc. to make a variation.In addition the research deficiency that, relevant portal venous pressure detects both at home and abroad is also: research range is confined to main portal vein, and the main genus that seldom relates to Portal system props up; Be confined to the piezometry at a certain position, the integral pressure of not setting up portal system distributes; Hemorheology Study is still in the starting stage, and the variation of blood viscosity and the reduction of erythrocyte deformability all can change the resistance of portal vein blood vessel.Therefore, in the urgent need to invent a kind of safe noinvasive, easy and simple to handle, intuitively quantize and the high evaluation methodology of portal vein hydromechanics and the pressure parameter detection technique of accuracy.

Present inventor, by the method for reconstruction, finite element analysis and the hematodinamics calculating of hepatic portal vein numerical model, sets up a kind of evaluation methodology of portal vein hydromechanics and pressure parameter detection technique that meets scientific research and clinical demand, thereby has completed the present invention.

Summary of the invention

The object of this invention is to provide the evaluation methodology of a kind of portal vein hydromechanics and pressure parameter detection technique, for physiology, pathophysiology research provide foundation, and further for clinical therapeutics is given a clue.

Portal vein hydromechanics of the present invention evaluation methodology comprises the following steps:

1. utilize thin-layer CT image, build hepatoportal 3-D geometric model;

2. with the finite element method of fluid calculation software ANSYS, after being divided, above-mentioned geometric model grid sets up out three-dimensional mathematical model;

3. the pylic hemodynamic parameter of analog computation, acquisition speed and pressure distribution design sketch.

The present invention adopts medical image to control software MIMICS and sets up geometric model, uses fluid calculation software ANSYS to set up three-dimensional mathematical model.Its feasibility analysis is as follows:

Arranged by the basic physical law such as the conservation of mass, the conservation of momentum and preservation of energy.Fluid Mechanics Computation is to show by computer numerical value calculation and image, to the analysis that includes that fluid flows and the system of the relevant physical phenomena such as conduction of heat is done.

Portal vein and Main Branches thereof are one section of crooked blood vessels with geometry, its tube wall does not have very large practical distortion amount, therefore the present invention is assumed to rigid pipe by blood vessel, wherein the viscosity of blood is lower and can be considered constant viscosity, be in the internal friction shearing force τ of fluid and unit distance the relative velocity between LAYER FLUID is approximated to linear relationship, and density is approximately constant, therefore the approximate Newtonian fluid that can not press that is assumed to be of blood in portal vein.

It is that the dimensionless parameter of laminar flow or turbulent flow is Reynolds number (Re) that judgement fluid flows, and is defined as R _e=ρ VD/ μ, wherein, ρ is fluid density, V is the mobile speed of fluid, the interior diameter that D is pipe, μ is fluid viscosity.Generally, R _eduring <2000, fluid is in laminar condition; R _eduring >3000, flow for turbulent flow.In preliminary experiment model, portal vein diameter 7mm, speed 21cm/s, fluid density 1.05 * 10 ³kg/m ³, fluid viscosity is 0.0035.As calculated, pylic Reynolds number R _e=819<2000, therefore blood is done laminar motion in portal vein.

Hydrodynamics software ANSYS carries out analog computation according to limited element analysis technique, by one, continuous solve the many small unit that territory is divided into arbitrarily suitable shape, and in each junior unit burst structure interpolating function, then according to extremum principle (variation or weighted residual method), the governing equation of problem is converted into the finite element equation on all unit, using overall extreme value as each unit extreme value sum, be about to local unit totally synthetic, formation has embedded the Algebraic Equation set of specified boundary condition, solves this equation group and obtains each node functional value to be asked.

Ignore the impact of gravity, we can adopt Three dimensional transient Navier-Stokes equation

$\frac{\&PartialD;\left(\mathrm{\&rho;u}\right)}{\&PartialD;t}+\mathrm{div}\left(\mathrm{\&rho;uu}\right)=\mathrm{div}\left(\mathrm{\&mu;}\mathrm{grad}u\right)-\frac{\&PartialD;p}{\&PartialD;x}+S_u$

$\frac{\&PartialD;\left(\mathrm{\&rho;v}\right)}{\&PartialD;t}+\mathrm{div}\left(\mathrm{\&rho;uu}\right)=\mathrm{div}\left(\mathrm{\&mu;}\mathrm{grad}u\right)-\frac{\&PartialD;p}{\&PartialD;x}+S_v$

$\frac{\&PartialD;\left(\mathrm{\&rho;w}\right)}{\&PartialD;t}+\mathrm{div}\left(\mathrm{\&rho;uu}\right)=\mathrm{div}\left(\mathrm{\&mu;}\mathrm{grad}u\right)-\frac{\&PartialD;p}{\&PartialD;x}+S_w$

In formula, s _u, S _v, S _wthe broad sense source item of momentum conservation equation, S _u=F _x+ s _x, S _v=F _y+ s _y, S _w=F _z+ s _z, and s wherein _x, s _y, s _zexpression formula as follows:

$s_x=\frac{\&PartialD;}{\&PartialD;x}\left(\mathrm{\&mu;}\frac{\&PartialD;u}{\&PartialD;x}\right)+\frac{\&PartialD;}{\&PartialD;y}\left(\mathrm{\&mu;}\frac{\&PartialD;v}{\&PartialD;x}\right)+\frac{\&PartialD;}{\&PartialD;z}\left(\mathrm{\&mu;}\frac{\&PartialD;w}{\&PartialD;x}\right)+\frac{\&PartialD;}{\&PartialD;x}\left(\mathrm{\&lambda;}\mathrm{div}u\right)$

$s_x=\frac{\&PartialD;}{\&PartialD;x}\left(\mathrm{\&mu;}\frac{\&PartialD;u}{\&PartialD;y}\right)+\frac{\&PartialD;}{\&PartialD;y}\left(\mathrm{\&mu;}\frac{\&PartialD;v}{\&PartialD;y}\right)+\frac{\&PartialD;}{\&PartialD;z}\left(\mathrm{\&mu;}\frac{\&PartialD;w}{\&PartialD;y}\right)+\frac{\&PartialD;}{\&PartialD;y}\left(\mathrm{\&lambda;}\mathrm{div}u\right)$

$s_z=\frac{\&PartialD;}{\&PartialD;x}\left(\mathrm{\&mu;}\frac{\&PartialD;u}{\&PartialD;z}\right)+\frac{\&PartialD;}{\&PartialD;y}\left(\mathrm{\&mu;}\frac{\&PartialD;v}{\&PartialD;z}\right)+\frac{\&PartialD;}{\&PartialD;z}\left(\mathrm{\&mu;}\frac{\&PartialD;w}{\&PartialD;z}\right)+\frac{\&PartialD;}{\&PartialD;z}\left(\mathrm{\&lambda;}\mathrm{div}u\right)$

Wherein λ is second viscosity, general desirable λ=-2/3.

By above-mentioned feasibility analysis, the present invention adopts medical image to control software MIMICS and fluid calculation software ANSYS sets up three dimensional door vein model, and then analog computation goes out the hemodynamic parameter of portal system.

Figure 1A-1C shows the concrete technical scheme of the invention described above method.

Structure hepatic portal vein 3-D geometric model in the inventive method step (1) specifically comprises: after obtaining CT data, import MIMICS software, automatically calculate and generate coronalplane and sagittal plane two dimension composite diagram; According to organizing grey value difference, passing threshold is set and is extracted fat and muscular tissue, then carries out scope and confine; Utilize MIMICS software multilamellar editting function editor to scheme layer, delete portal vein and belong to its outer hetero-organization, carry out three-dimensional reconstruction; Each tomography picture is manually filled up to pixel, smooth, cutting, to repair the blood vessel wall surface hole because of the different generation of CT value difference; Model after processing is exported as to ANSYS file (Figure 1A).

In the step of the inventive method (2), the foundation of three-dimensional mathematical model specifically comprises: with 3-D geometric model face, import ANSYS, in ANSYS software, generate solid; Model gateway is truncated into blood vessel and moves towards vertical plane; Threedimensional model is divided into limited tetrahedron, as grid cell, generates computing node; Set up discrete initial and boundary condition; Parameter (density and viscosity), the number of times of given iterative computation and control accuracy etc. (Figure 1B) are controlled in solving of given governing equation.

The step of the inventive method (3) is to obtain portal vein and the three-dimensional of branch or the speed of arbitrary plane and pressure-plotting.

After the calculating of the Flotran of ANSYS module finishes, can obtain speed and the pressure distributed in three dimensions design sketch of portal vein and branch thereof.Because this technology is to simulate in vitro, therefore can utilize different two dimensional surfaces, carry out multi-angle truncated models, obtain speed and the pressure distribution of arbitrary plane in space, and then the blood flow motion conditions of analyzing three-dimensional portal system.The three-dimensional pressure distribution, portal vein sagittal plane pressure (I) and speed (II) scattergram and portal vein transverse section pressure (I) and speed (II) scattergram that in Fig. 1 C, have shown portal system.

Fig. 2 shows that abdominal CT is conventionally strengthened to image to be imported iconography and control in software MIMICS, the hepatic portal vein 3-D geometric model reconstructing.Fig. 3 shows the finite element method that uses fluid calculation software ANSYS, after geometric model grid is divided, sets up out three-dimensional mathematical model.

Fig. 4 and Fig. 5 show respectively by setting discrete boundary condition, solving and control after parameter, iterations and control accuracy, simulate hepatoportal blood flow motion and HVPG and portal venous pressure and the VELOCITY DISTRIBUTION design sketch of acquisition.

The beneficial effect of the invention

The present invention combines with applied mathematics, hydromechanical intersection by physiology, pathophysiology, obtained a kind of safe noinvasive, easy and simple to handle, intuitively quantize and the high evaluation methodology of portal vein hydromechanics and the pressure parameter detection technique of accuracy.Meanwhile, also set up one and can, for clinical and valid model Scientific Research Service, the pressure distribution of hepatic portal vein and branch thereof organically have been contacted into an integral body.Therefore, the present invention can solve the actual needs of portal venous flow kinetics being evaluated at present to a great extent both at home and abroad, has made up preferably the deficiency of related discipline research.

" science and engineering doctor " of the present invention multidisciplinary crossed dominance and novelty, is also embodied in following five aspects:

(1) novelty of technology: be used at present assessing mostly being non-specificity index and being difficult to quantification of portal venous pressure in clinical position.This project utilizes interactive image to control software and finite element analysis software, in the hepatic portal vein three-dimensional modeling enterprising promoting the circulation of blood hydromechanics in basis and rheology, calculates, and obtains the hemodynamic index of objective quantification.Research about this respect there is not yet report at present both at home and abroad.

(2) integrity of model: the main deficiency of correlational study is to be confined to main portal vein both at home and abroad at present, seldom relates to the Main Branches of Portal system; What be confined to concrete position has a piezometry of wound property, and does not set up whole its distribution of theoretical model analysis pressure.Yet the main genus that effective theoretical model must comprise portal system props up, and correctly reflect the constitutive relation of each branch and interrelated.The model that this technology is set up, is distributed with machine by the pressure of hepatic portal vein and branch thereof, speed etc. first and contacts into an integral body, thereby more profoundly reflect the blood flow motion conditions of portal system.Research about this respect there is not yet report at present both at home and abroad.

(3) pressure distribution is directly perceived: the technical difficulty of measuring at present directly portal venous pressure is high, serious complication greatly, easily occurs wound; In indirect determination, lack again the index of specificity and good relationship.The Three-dimension Reconstruction Model that this technology is used, spatial impression is strong.Utilize finite element analysis and hydrodynamic methods to calculate hepatoportal pressure-plotting, thus make multiaxis to multi-angular analysis blood flow move into for may, and provide certain foundation for the design of surgical method.Research about this respect there is not yet report at present both at home and abroad.

(4) consider portal system VELOCITY DISTRIBUTION: research finds, the blood flow rate of portal system (size and direction) is stocked with liver function, the selection of art formula, life cycle length have close relationship.Yet color doppler ultrasonography can only rest on two dimensional surface for the analysis of speed, and stronger to operator's subjective dependency.Method of the present invention can obtain the speed of each point in three-dimensional hepatic portal system, thereby simulates hepatoportal blood flow motion conditions.Research about this respect there is not yet report at present both at home and abroad.

(5) consider hemorheology: compare with hematodinamics, the Hemorheology Study of portal system is still in the starting stage.Clinical and lab testing finds, the blood constituents such as platelet count, leukocyte change, and blood viscosity changes and the reduction of erythrocyte deformability all can change the resistance of portal vein blood vessel, and then affect its hemodynamic parameter.The present invention, when the hydrodynamics motion of simulated main portal vein blood and calculating pressure parameter, has considered that hemorheology change is on hemodynamic impact.The current domestic and international rarely seen report of research about this respect.

Brief description of drawings

Fig. 1 is Technology Roadmap, and wherein Figure 1A is for utilizing thin-layer CT picture construction geometric model; Figure 1B is for utilizing blood flow motion correlated characteristic to set up mathematical model; Fig. 1 C is the pylic hemodynamic parameter of analog computation, acquisition speed and pressure distribution design sketch.

Fig. 2 is for controlling by iconography the hepatic portal vein 3-D geometric model that software MIMICS reconstructs.

Fig. 3 is that finite element grid builds three-dimensional mathematical model schematic diagram.

Fig. 4 is HVPG schematic diagram.

Fig. 5 is hepatic portal vein barometric gradient schematic diagram.

Fig. 6 is the statistical of portal venous pressure virtual value (the inventive method income value) and direct measured value.

Fig. 7 is the correlation analysis of portal venous pressure virtual value (the inventive method income value) and direct measured value.

The specific embodiment

For a more detailed description to the present invention with embodiment below.These embodiment are only the descriptions to best mode for carrying out the invention, scope of the present invention are not had to any restriction.

Embodiment 1 sets up geometric model

By gathering the CT obtaining in GE Medical Systems work platforms, strengthen picture, export as dicom form, bed thickness 1.250mm, amounts to 570 layers, image resolution ratio 512 pixel * 512 pixels, Pixel Dimensions 0.797mm.Picture imports to medical image and controls in software MIMICS, and software calculates two dimensional surface (coronalplane, the sagittal plane) composite diagram that generates portal system automatically.Different according to the CT value difference of blood vessel and surrounding tissue, passing threshold is set, and extracts the tissues such as fat and muscle, then research range is limited, and obtains pylic preliminary threedimensional model.Due to portal vein and branch more difficult directly separated in threedimensional model with surrounding tissue, therefore, utilize the edit operation of MIMICS multilamellar, the tissue outside research range is deleted in selected region of interest simultaneously, reconstructs the model of portal vein and branch thereof.Because CT imaging noise is many, the model surface of generation can produce more cavity.Therefore, all coronalplanes or sagittal tomography picture are carried out to craft again and fill up pixel, obtain the solid door vein model of inner chamber sealing.Model is carried out after smooth treatment, export as ANSYS face Parameter File.

Embodiment 2 sets up mathematical model

Geometric model is imported to the Flotran module of fluid calculation software ANSYS, generate body file, set up numerical model.Utilize the planar interception vascular pattern vertical with blood flow direction to obtain entrance and exit.According to finite element theory, use three-dimensional tetrahedron element to carry out grid division to internal blood vessel, grid number amounts to 848432,150796 of computing nodes.In order to obtain pressure and the VELOCITY DISTRIBUTION of portal system, three-dimensional blood vessel model is carried out to local mesh reflnement, to improve computational accuracy.Subsequently, discrete initial boundary condition is set: 1. the blood flow rate 0cm/s of blood vessel wall place; 2. main portal vein speed 15.8cm/s; 3. blood vessel exports terminal pressure 10mmHg.Subsequently, required control parameter (blood viscosity=4.90mpas, density of blood=1.05 * 10 of given solving equation ³kg/m ³), set and calculate iterations 100.In computational process, the convergence of Real-Time Monitoring solution.

Acquisition and the analysis of embodiment 3 speed and pressure-plotting

After the calculating of the Flotran of ANSYS module finishes, can obtain speed and the pressure whole structure figure of three dimensional door vein and branch thereof.Can find out that portal system force value reduces gradually from supreme bring out mouthful (portal vein end enters liver) of lower end entrance (superior mesenteric vein and the splenic vein).Because the present invention is in-vitro simulated technology, therefore can multi-angle rotary and observe pressure distribution.In addition, we utilize perpendicular to pylic sagittal plane truncated models, can obtain speed and the pressure-plotting of internal blood vessel.VELOCITY DISTRIBUTION prompting: converge to into liver from portal vein, blood flow rate increases gradually because caliber attenuates; The speed integral body of blood vessel lateral wall is lower than medial wall, and this is consistent with the ultimate principle of Bernoulli equation.Pressure distribution prompting: the pressure of blood vessel lateral wall is significantly higher than medial wall.Meanwhile, utilize a plurality of transverse section to be interrupted the change that truncated models is dynamically observed blood flow motion.Transverse section before the splenic vein and superior mesenteric vein converge (aa ', bb ') locate, because blood vessel is without obvious geometry deformation, pressure distribution is more regular, and VELOCITY DISTRIBUTION presents the low parabolic type of the high periphery in center; To vein, converge (cc ') and locate, blood vessel lateral wall pressure starts to raise, and central speed offsets to splenic vein side; At main portal vein section (dd ', ee '), locate, because blood vessel occurs bending and deformation, pressure distribution shows as by inner side to lateral wall and raises gradually, and velocity bias also occurs more obviously to change.

Experimental example 1

In order to verify the effect of the inventive method, we enter to have organized 11 routine objects altogether.The portal venous flow velocity simulate that utilizes every group of data epigastrium CT enhancing picture and color doppler ultrasonography to record calculates virtual portal venous pressure; In operation, utilize water column method directly to measure portal venous pressure as " goldstandard " simultaneously.The inventive method gained virtual value is shown in Fig. 6 with the statistical result of direct two groups of data of measured value.The dependency (r=0.748, p=0.008) of further analyzing two groups of pressure datas is as Fig. 7.Statistical result shows, the type gate vein pressure virtual test technique the present invention relates to has higher accuracy.

Claims (6)

1. a portal vein hydromechanics evaluation methodology, comprises the following steps:

(1) utilize thin-layer CT image, build hepatoportal 3-D geometric model;

(2) with the finite element method of fluid calculation software ANSYS, step (1) gained geometric model is carried out setting up out three-dimensional mathematical model after grid division;

(3) the pylic hemodynamic parameter of analog computation, acquisition speed and pressure distribution design sketch.

2. the method for claim 1, wherein step (1) comprising: after obtaining CT data, import MIMICS software, automatically calculate and generate coronalplane and sagittal plane two dimension composite diagram; According to organizing grey value difference, passing threshold is set and is extracted fat and muscular tissue, then carries out scope and confine; Utilize MIMICS software multilamellar editting function editor to scheme layer, delete portal vein and belong to its outer hetero-organization, carry out three-dimensional reconstruction; Each tomography picture is manually filled up to pixel, smooth, cutting, to repair the blood vessel wall surface hole because of the different generation of CT value difference; Model after processing is exported as to ANSYS file.

3. the method for claim 1, wherein step (2) comprising: with 3-D geometric model face, import ANSYS, in ANSYS software, generate solid; Model gateway is truncated into blood vessel and moves towards vertical plane; Threedimensional model is divided into limited tetrahedron, as grid cell, generates computing node; Set up discrete initial and boundary condition; Given governing equation solve control parameter, the number of times of given iterative computation and control accuracy.

4. method as claimed in claim 3, it is density and viscosity that the solving of wherein said equation controlled parameter.

5. the method for claim 1, wherein step (3) comprising: obtain portal vein and the three-dimensional of branch or the speed of arbitrary plane and pressure-plotting.

6. method as claimed in claim 5, wherein said arbitrary plane comprises sagittal plane and transverse section.