基于格子Boltzmann方法的個(gè)體化顱內(nèi)動(dòng)脈瘤幾何重建及其數(shù)值模擬
發(fā)布時(shí)間：2018-08-25 14:48
【摘要】：顱內(nèi)動(dòng)脈瘤是危害人類健康的最危險(xiǎn)和最常見(jiàn)疾病之一,而血流動(dòng)力學(xué)作為影響顱內(nèi)動(dòng)脈瘤產(chǎn)生、發(fā)展、破裂和治療的主要因素,受到國(guó)內(nèi)外學(xué)者的廣泛關(guān)注。在臨床治療方面,血流轉(zhuǎn)向支架和彈簧圈栓塞的血管內(nèi)部介入治療手段取得了好的療效,但支架和彈簧圈的工業(yè)設(shè)計(jì)仍需要理論和實(shí)驗(yàn)的進(jìn)一步改善。但是傳統(tǒng)的臨床實(shí)驗(yàn)面臨風(fēng)險(xiǎn)大、周期長(zhǎng)、成本高的困境。目前基于醫(yī)學(xué)圖像的個(gè)體化顱內(nèi)動(dòng)脈瘤數(shù)值實(shí)驗(yàn)受到青睞�，F(xiàn)有的數(shù)值研究方法大多采用各種計(jì)算流體力學(xué)(CFD)軟件,在使用過(guò)程中受到血管復(fù)雜幾何結(jié)構(gòu)、血液流動(dòng)特性、低計(jì)算效率等諸多問(wèn)題的限制。 近年來(lái),格子Boltzmann方法(LBM)因其在計(jì)算流體力學(xué)方面的快速發(fā)展越來(lái)越備受矚目。在模型的通用性、處理復(fù)雜邊界的能力和計(jì)算的效率上,LB方法有其天然的優(yōu)勢(shì),適合用于顱內(nèi)動(dòng)脈瘤血流動(dòng)力學(xué)的模擬和分析。此外,很多學(xué)者已將LB方法作為一種有效的數(shù)值方法用于求解各種偏微分方程,如：對(duì)流擴(kuò)散方程、反應(yīng)擴(kuò)散方程、泊松方程等。 目前,基于LBM的動(dòng)脈瘤血流動(dòng)力學(xué)數(shù)值模擬已有一些研究工作,但是在動(dòng)脈瘤幾何模型上已有的工作大多基于二維的模型或者圓柱加圓球組合的理想三維模型,缺乏個(gè)體化病人的研究；在病人個(gè)體化數(shù)據(jù)的研究中,數(shù)值模擬的進(jìn)出口邊界條件仍需要討論。在此基礎(chǔ)上,本文以LBM為主要的數(shù)值手段研究個(gè)體化顱內(nèi)動(dòng)脈瘤血流動(dòng)力學(xué)模擬的整個(gè)過(guò)程：從臨床采集的三維斷層醫(yī)學(xué)影像數(shù)據(jù)出發(fā),通過(guò)發(fā)展多種格子Boltzmann模型,并借助圖形處理器(GPU)并行計(jì)算設(shè)備完成個(gè)體病人血管圖像分割、幾何重建、LBM計(jì)算網(wǎng)格處理和血流動(dòng)力學(xué)模擬。 論文的工作主要包括兩個(gè)方面：個(gè)體化動(dòng)脈瘤幾何外形的重建和復(fù)雜邊界的血流動(dòng)力學(xué)數(shù)值模擬。在幾何外形重建和計(jì)算網(wǎng)格方面： (1)本文通過(guò)對(duì)格子Boltzmann方法求解方程的特點(diǎn)和基于偏微分方程的圖像去噪、邊緣檢測(cè)、圖像分割模型特點(diǎn)的研究,提出一種能高效解決圖像去噪,邊緣檢測(cè)和圖像分割的LB模型,并將此模型運(yùn)用于個(gè)體化顱內(nèi)動(dòng)脈瘤斷層CT圖像數(shù)據(jù)處理之中,能夠準(zhǔn)確的完成個(gè)體化動(dòng)脈瘤三維幾何模型的圖像分割。該模型不僅僅能運(yùn)用于醫(yī)學(xué)圖像,對(duì)于更為復(fù)雜的自然圖片的輪廓檢測(cè)和圖像分割也具有良好的效果。 (2)為了達(dá)到格子Boltzmann方法計(jì)算網(wǎng)格和臨床研究的需求,我們對(duì)幾何模型做了進(jìn)一步改進(jìn),使得幾何模型更加合理�；趫D像分割的結(jié)果,我們提出血管中心線方法,重建載瘤血管和血管支架。一方面,使得載瘤血管更加光滑,更接近實(shí)際情況；另一方面,可以根據(jù)研究需要隨意取舍動(dòng)脈瘤附近分支血管。通過(guò)與傳統(tǒng)CFD軟件重建的三維模型的對(duì)比,本文提出的幾何模型處理結(jié)果更為合理,且滿足各種類型血管支架的設(shè)計(jì)。 在復(fù)雜邊界的血流動(dòng)力學(xué)數(shù)值模擬方面： (1)在血管幾何模型的基礎(chǔ)上,我們發(fā)展基于復(fù)雜邊界的格子Boltzmanr模型,以此求解描述血流動(dòng)力學(xué)的Navier-Stokes方程。同時(shí)也探討個(gè)體化顱內(nèi)動(dòng)脈瘤進(jìn)出口條件。研究發(fā)現(xiàn)采用速度進(jìn)口,壓力出口條件更適合各種個(gè)體化顱內(nèi)動(dòng)脈瘤幾何模型的需求。此外,在速度進(jìn)口與壓力出口的邊界條件下,討論了脈動(dòng)速度進(jìn)口與定常速度進(jìn)口的區(qū)別,發(fā)現(xiàn)采用脈動(dòng)速度均值和脈動(dòng)峰值的平均值作為定常速度進(jìn)口可以近似模擬血流脈動(dòng)峰值時(shí)刻的流動(dòng)狀態(tài)。 (2)結(jié)合臨床治療中的問(wèn)題,我們對(duì)多例頸動(dòng)脈瘤病人數(shù)據(jù)的進(jìn)行了數(shù)值模擬。針對(duì)血管支架的設(shè)計(jì)問(wèn)題,本文研究了不同疏密和類型的血管支架置入載瘤血管后瘤內(nèi)血流動(dòng)力學(xué)變化。發(fā)現(xiàn)支架置入之后動(dòng)脈瘤內(nèi)部流線形態(tài)發(fā)生明顯變化,血流速度明顯減小,且隨著支架密度的增大而減小得更顯著,同樣疏密的螺旋網(wǎng)狀支架比單螺旋支架更能抑制瘤內(nèi)速度；研究了動(dòng)脈瘤附近支血管對(duì)瘤內(nèi)血流動(dòng)力學(xué)的影響,并通過(guò)對(duì)瘤內(nèi)部速度大小和流態(tài)的分析得出當(dāng)載瘤血管與支血管直徑比較大或者分支血管距離動(dòng)脈瘤較遠(yuǎn)時(shí),瘤內(nèi)流場(chǎng)差異較小。在數(shù)值研究中可以根據(jù)需要去除這部分分支血管。 總之,本文以格子Boltzmann方法為主要數(shù)值手段,建立了個(gè)體化顱內(nèi)動(dòng)脈瘤血流動(dòng)力學(xué)模擬的整套方案,并在GPU高性能并行平臺(tái)下完成了LB算法的設(shè)計(jì),相比CPU程序得到近兩個(gè)數(shù)量級(jí)的加速比,大大提高了數(shù)值模擬算法的效率。與此同時(shí),本文針對(duì)臨床病例開(kāi)展數(shù)值研究,分析了各種幾何模型對(duì)于血流動(dòng)力學(xué)的影響,并通過(guò)臨床的對(duì)比得到了定性上的驗(yàn)證。為進(jìn)一步探索動(dòng)脈瘤治療手段,本文將兩種螺旋支架數(shù)字化置入個(gè)體化病人動(dòng)脈瘤幾何模型中,一方面通過(guò)數(shù)值模擬對(duì)臨床治療給出了理論上的解釋,另一方面對(duì)臨床血管支架置入選擇和置入位置給予了指導(dǎo)。
[Abstract]:Intracranial aneurysms are one of the most dangerous and common diseases that endanger human health. Hemodynamics, as a major factor affecting the generation, development, rupture and treatment of intracranial aneurysms, has attracted wide attention of scholars both at home and abroad. In clinical treatment, interventional therapy with blood flow diversion stent and coil embolization has been achieved. However, the traditional clinical trials are faced with the difficulties of high risk, long cycle and high cost. At present, individual numerical experiments based on medical images are favored. Most of the existing numerical methods use various computational flows. Body mechanics (CFD) software is limited by the complex geometry of blood vessels, the characteristics of blood flow and the low computational efficiency.
In recent years, lattice Boltzmann method (LBM) has attracted more and more attention because of its rapid development in computational fluid dynamics. LB method has its natural advantages in the generality of models, the ability to deal with complex boundaries and the efficiency of computation. It is suitable for the simulation and analysis of intracranial aneurysm hemodynamics. As an effective numerical method, the method is used to solve various partial differential equations, such as convection-diffusion equation, reaction-diffusion equation and Poisson equation.
At present, there are some research work on the numerical simulation of aneurysm hemodynamics based on LBM, but most of the work on the geometric model of aneurysm is based on the two-dimensional model or the ideal three-dimensional model combined with cylinder and sphere, lacking of individual patient research; in the study of individual patient data, the import and export of numerical simulation. On this basis, the whole process of individualized hemodynamic simulation of intracranial aneurysms is studied by using LBM as the main numerical means: starting from the clinical acquired three-dimensional tomographic medical image data, a variety of lattice Boltzmann models are developed and implemented with the help of a graphics processor (GPU) parallel computing device. Individual patient's blood vessel image segmentation, geometric reconstruction, LBM computational grid processing and hemodynamics simulation.
The work of this paper includes two aspects: reconstruction of the geometric shape of aneurysm and numerical simulation of hemodynamics with complex boundary.
(1) By studying the characteristics of the lattice Boltzmann method and the image denoising, edge detection and image segmentation model based on PDE, this paper proposes a LB model which can efficiently solve image denoising, edge detection and image segmentation, and applies this model to the computed tomography image of intracranial aneurysms. In principle, the 3D geometric model of individual aneurysms can be accurately segmented. The model can not only be applied to medical images, but also has a good effect on contour detection and image segmentation of more complex natural images.
(2) In order to meet the needs of grid computing and clinical research, we have further improved the geometric model to make the geometric model more reasonable. Based on the results of image segmentation, we propose a vascular center line method to reconstruct tumor-bearing vessels and vascular stents. On the other hand, the branches near the aneurysms can be freely removed according to the needs of the study. Compared with the three-dimensional models reconstructed by traditional CFD software, the geometric model presented in this paper is more reasonable and can meet the design of various types of vascular stents.
In the numerical simulation of complex boundary hemodynamics,
(1) Based on the vascular geometry model, we developed a lattice Boltzmanr model with complex boundary to solve the Navier-Stokes equations describing hemodynamics. We also discussed the individualized inlet and outlet conditions of intracranial aneurysms. In addition, under the boundary conditions of the velocity inlet and the pressure outlet, the difference between the pulsatile velocity inlet and the steady velocity inlet is discussed. It is found that the flow state at the peak time of the pulsatile flow can be approximately simulated by using the mean value of the pulsatile velocity and the mean value of the pulsatile peak value as the steady velocity inlet.
(2) Combining with the problems in clinical treatment, we simulated the data of several patients with carotid aneurysms. Aiming at the design of stents, we studied the hemodynamic changes in aneurysms after implantation of different dense and different types of stents. With the increase of stent density, the same dense spiral mesh stent can inhibit the intratumoral velocity more effectively than single spiral stent. The effect of the branches near the aneurysm on the intratumoral hemodynamics was studied, and the velocity and flow pattern inside the aneurysm were analyzed. The flow field in the aneurysm is smaller when the diameter of the branch is larger or the branch is farther away from the aneurysm.
In a word, this paper takes the lattice Boltzmann method as the main numerical means, establishes the whole scheme of individual intracranial aneurysm hemodynamics simulation, and completes the design of LB algorithm under the high performance parallel platform of GPU. Compared with the CPU program, the acceleration ratio of nearly two orders of magnitude is obtained, which greatly improves the efficiency of numerical simulation algorithm. In order to further explore the treatment of aneurysms, two kinds of spiral stents were digitally implanted into the geometric models of individual patients with aneurysms. On the one hand, the numerical models were used. This paper provides a theoretical explanation for the clinical treatment, on the other hand, it provides guidance for the selection and placement of clinical vascular stents.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TP391.41;R739.41
本文編號(hào)：2203205
[Abstract]:Intracranial aneurysms are one of the most dangerous and common diseases that endanger human health. Hemodynamics, as a major factor affecting the generation, development, rupture and treatment of intracranial aneurysms, has attracted wide attention of scholars both at home and abroad. In clinical treatment, interventional therapy with blood flow diversion stent and coil embolization has been achieved. However, the traditional clinical trials are faced with the difficulties of high risk, long cycle and high cost. At present, individual numerical experiments based on medical images are favored. Most of the existing numerical methods use various computational flows. Body mechanics (CFD) software is limited by the complex geometry of blood vessels, the characteristics of blood flow and the low computational efficiency.
In recent years, lattice Boltzmann method (LBM) has attracted more and more attention because of its rapid development in computational fluid dynamics. LB method has its natural advantages in the generality of models, the ability to deal with complex boundaries and the efficiency of computation. It is suitable for the simulation and analysis of intracranial aneurysm hemodynamics. As an effective numerical method, the method is used to solve various partial differential equations, such as convection-diffusion equation, reaction-diffusion equation and Poisson equation.
At present, there are some research work on the numerical simulation of aneurysm hemodynamics based on LBM, but most of the work on the geometric model of aneurysm is based on the two-dimensional model or the ideal three-dimensional model combined with cylinder and sphere, lacking of individual patient research; in the study of individual patient data, the import and export of numerical simulation. On this basis, the whole process of individualized hemodynamic simulation of intracranial aneurysms is studied by using LBM as the main numerical means: starting from the clinical acquired three-dimensional tomographic medical image data, a variety of lattice Boltzmann models are developed and implemented with the help of a graphics processor (GPU) parallel computing device. Individual patient's blood vessel image segmentation, geometric reconstruction, LBM computational grid processing and hemodynamics simulation.
The work of this paper includes two aspects: reconstruction of the geometric shape of aneurysm and numerical simulation of hemodynamics with complex boundary.
(1) By studying the characteristics of the lattice Boltzmann method and the image denoising, edge detection and image segmentation model based on PDE, this paper proposes a LB model which can efficiently solve image denoising, edge detection and image segmentation, and applies this model to the computed tomography image of intracranial aneurysms. In principle, the 3D geometric model of individual aneurysms can be accurately segmented. The model can not only be applied to medical images, but also has a good effect on contour detection and image segmentation of more complex natural images.
(2) In order to meet the needs of grid computing and clinical research, we have further improved the geometric model to make the geometric model more reasonable. Based on the results of image segmentation, we propose a vascular center line method to reconstruct tumor-bearing vessels and vascular stents. On the other hand, the branches near the aneurysms can be freely removed according to the needs of the study. Compared with the three-dimensional models reconstructed by traditional CFD software, the geometric model presented in this paper is more reasonable and can meet the design of various types of vascular stents.
In the numerical simulation of complex boundary hemodynamics,
(1) Based on the vascular geometry model, we developed a lattice Boltzmanr model with complex boundary to solve the Navier-Stokes equations describing hemodynamics. We also discussed the individualized inlet and outlet conditions of intracranial aneurysms. In addition, under the boundary conditions of the velocity inlet and the pressure outlet, the difference between the pulsatile velocity inlet and the steady velocity inlet is discussed. It is found that the flow state at the peak time of the pulsatile flow can be approximately simulated by using the mean value of the pulsatile velocity and the mean value of the pulsatile peak value as the steady velocity inlet.
(2) Combining with the problems in clinical treatment, we simulated the data of several patients with carotid aneurysms. Aiming at the design of stents, we studied the hemodynamic changes in aneurysms after implantation of different dense and different types of stents. With the increase of stent density, the same dense spiral mesh stent can inhibit the intratumoral velocity more effectively than single spiral stent. The effect of the branches near the aneurysm on the intratumoral hemodynamics was studied, and the velocity and flow pattern inside the aneurysm were analyzed. The flow field in the aneurysm is smaller when the diameter of the branch is larger or the branch is farther away from the aneurysm.
In a word, this paper takes the lattice Boltzmann method as the main numerical means, establishes the whole scheme of individual intracranial aneurysm hemodynamics simulation, and completes the design of LB algorithm under the high performance parallel platform of GPU. Compared with the CPU program, the acceleration ratio of nearly two orders of magnitude is obtained, which greatly improves the efficiency of numerical simulation algorithm. In order to further explore the treatment of aneurysms, two kinds of spiral stents were digitally implanted into the geometric models of individual patients with aneurysms. On the one hand, the numerical models were used. This paper provides a theoretical explanation for the clinical treatment, on the other hand, it provides guidance for the selection and placement of clinical vascular stents.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TP391.41;R739.41
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