本文選題：有限元分析 + 脊柱��； 參考：《南方醫(yī)科大學(xué)》2013年碩士論文

【摘要】：背景： 數(shù)字醫(yī)學(xué)概念的提出促進了有限元技術(shù)與醫(yī)學(xué)的結(jié)合,CT數(shù)據(jù)集在三維重建方面的廣泛應(yīng)用更加快了這一進程的發(fā)展,尤其是在骨骼模型的構(gòu)建方面顯得特別突出。三維有限元模型可以用于正常骨骼的應(yīng)力應(yīng)變分析,也可用于分析其發(fā)生骨折的危險系數(shù)或內(nèi)固定物的微動情況。在國外,O'Reilly和Whyn, Schmidt等,Little等,Schileo等,Yosibash等對脊柱和股骨等部位進行了相關(guān)的研究。在國內(nèi)有限元方面研究也逐漸加深,特別是數(shù)字醫(yī)學(xué)概念的提出更是把有限元技術(shù)與醫(yī)學(xué)方面結(jié)合起來。很多學(xué)者在有限元仿真等領(lǐng)域做出相應(yīng)的研究。 有限元建模是指建立一個可以由計算機順利計算的數(shù)字模型,該模型要和現(xiàn)實中物理模型的力學(xué)性能相一致,其實質(zhì)是用有限元方法在計算機的虛擬環(huán)境中建立一個數(shù)字模型,這個模型有以下要求：一,要保證力學(xué)的完整性；二：要保證計算的有效性。即建立的有限元模型有兩個使命,對上要承載完整的力學(xué)信息,對下要保證計算機可以快速準(zhǔn)確的計算。在建立有限元模型的過程中既要保證所建模型外形與現(xiàn)實相近,也要使模型的一些力學(xué)材料性能與真實情況盡量相符。Marom等認為CT掃描可以反映出骨骼模型的高特征性。CT掃描作為一種臨床常規(guī)體外非侵入性的診斷方法,它不僅可以提供骨骼精確的幾何學(xué)信息,更可以提供骨骼相關(guān)的機械性能參數(shù)�，F(xiàn)階段,CT數(shù)據(jù)在有限元領(lǐng)域的最主要用途在于骨骼三維模型構(gòu)建,而對于有限元模型構(gòu)建的另一個重要組成部分：材料屬性賦值,卻甚少涉及。骨骼是醫(yī)學(xué)有限元分析的主要對象之一,人骨的材料屬性更是十分復(fù)雜的,個體差異明顯,不同人或同一人體不同部位之間都存在差別。傳統(tǒng)的骨骼材料屬性劃分方法是將骨單純分為皮質(zhì)骨和松質(zhì)骨兩部分進行賦值,這樣劃分必然與人骨材料屬性復(fù)雜性不符,在計算中不免會出現(xiàn)較大誤差。隨著人們對CT數(shù)據(jù)認識的加深和相應(yīng)軟件的開發(fā)運用,逐漸開發(fā)出的一類軟件如MIMICS, BONEMAT, AMAB等,這些軟件可以把CT數(shù)據(jù)作為一種內(nèi)部的數(shù)據(jù)代碼與有限元仿真模型相結(jié)合,其分配方案是根據(jù)CT數(shù)據(jù)的灰度值來決定有限元模型的材料屬性的,具體方法是通過提取出單元體積內(nèi)所有CT圖像的像素值,并計算出其平均值來賦予到該單元中。這種方法可以最終達到通過CT灰度值確定有限元模型中每個單元彈性模量的目的。 醫(yī)學(xué)圖像的三維重建及可視化技術(shù)是一種運用計算機圖形學(xué)、圖像處理、計算機視覺以及人機交互技術(shù)將醫(yī)學(xué)圖像數(shù)據(jù)轉(zhuǎn)換為圖形或圖像在屏幕上顯示出來,并進行交互處理的理論、方法和技術(shù)。MIMICS是Materialise公司研發(fā)的交互式的醫(yī)學(xué)影像控制系統(tǒng)(Materialise's interactive medical image control system),是一套高度整合而且易用的3D圖像生成及編輯處理軟件,它能輸入各種醫(yī)學(xué)影像(CT、MRI)數(shù)據(jù),建立3D模型進行編輯,在PC機上進行大規(guī)模數(shù)據(jù)的轉(zhuǎn)換處理。該軟件除了可以運用于構(gòu)建3D模型,更可以將CT灰度值與模型的材料屬性聯(lián)系起來,按照一定的劃分梯度對模型的材料屬性進行賦值。一個較好的賦值方法,配合一個較好的分配方案,可以改善計算中因個體差異造成的誤差。本實驗就是在MIMICS軟件的基礎(chǔ)上在完成較好的幾何重建的前提下,運用其材料屬性分配模塊對模型的彈性模量按照不同分配梯度進行賦值,并將這些賦值后模型的有限元分析結(jié)果進行比較,再將其與手動賦值方法模型有限元結(jié)果比較,得出較好的賦值方法。通過研究兩種賦值方法(CT灰度值賦值法、手動賦值法)及CT灰度值賦值法中不同梯度變化對有限元分析結(jié)果的影響,得出一個相對經(jīng)濟、準(zhǔn)確的劃分梯度,為將該法在有限元研究中的應(yīng)用特別是臨床相關(guān)快速建模分析等方面提供相關(guān)的理論依據(jù)。 椎骨有限元建模 本部分內(nèi)容重點對課題實施的前期建模工作進行歸納總結(jié),闡述了相關(guān)的方法和技術(shù),細致的說明了本實驗進行有效建模的全過程。有限元分析是近年來在生物力學(xué)領(lǐng)域仿真人體結(jié)構(gòu)力學(xué)功能的一個重要實驗手段。通過建立人體有限元分析模型,賦予模型相應(yīng)的材料屬性并合理模擬在體條件,可以有效地分析人體結(jié)構(gòu)的物理性質(zhì)。其中,建立有限元幾何模型是有限元仿真分析的基礎(chǔ),其目的就在于為進一步的有限元分析過程提供一個物理框架,然后可以對這個框架進行相應(yīng)的修飾完善,最終達到可以完成分析的目標(biāo)。本部分內(nèi)容就是以胸腰椎標(biāo)本為例來說明相應(yīng)骨骼有限元模型建立的一般流程技術(shù)方法及注意事項。重點闡述了對三維重建中構(gòu)造幾何模型的過程,通過相應(yīng)的Remesh操作提高有限元網(wǎng)格劃分成功率及質(zhì)量的方法,以及使用geomagic軟件處理相應(yīng)三維模型得到理想有限元模型的方法。 自動分配方法中材料屬性分配梯度對椎骨有限元模型力學(xué)性能的影響 [目的] 研究以灰度值為基礎(chǔ)的不同材料屬性分配梯度對椎骨有限元模型力學(xué)性能的影響。 [方法] 對一位健康成人脊柱(T12～L5節(jié)段)進行快速CT薄層掃描,在MIMICS中對每節(jié)椎骨進行三維重建,通過Geomagic軟件處理后,導(dǎo)入ANSYS中進行網(wǎng)格劃分,再返回到MIMICS中按2,4,8,10,50,100,200,400份等8種梯度對材料屬性進行分配,最后重新導(dǎo)入ANSYS軟件按照同一載荷條件進行有限元分析。 [結(jié)果] 2、4、400這三個分配梯度與其它分配梯度相比,應(yīng)力情況存在顯著性差異(P0.05),而8、10、50、100、200梯度之間計算結(jié)果偏差不大。 [結(jié)論] 有限元模型材料屬性劃分不宜過多或過少,10份左右的劃分梯度既可保證運算結(jié)果的精確性,也相對可以提高運算速度,尤其適用于臨床個性化快速有限元建模。 材料屬性手動分配法與自動分配法對椎骨有限元模型力學(xué)性能的影響 [目的] 研究自動分配方法與手動賦值法對椎骨有限元模型力學(xué)性能的影響。 [方法] 對一位健康成人脊柱(T12-L5)進行快速CT薄層掃描,在MIMICS中對每節(jié)椎骨進行三維重建,通過Geomagic軟件處理后導(dǎo)回MIMICS中進行Remesh處理,然后導(dǎo)入ANSYS中進行網(wǎng)格劃分。材料屬性按兩種方法劃分：一、手動賦值法,直接在ANSYS中選取外圍單元賦予皮質(zhì)骨屬性,其它單元賦予松質(zhì)骨屬性；二、CT灰度值賦值法(自動分配法),模型導(dǎo)回到MIMICS中按照10份得分配梯度進行材料屬性的賦值。最后在ANSYS中進行有限元分析。 [結(jié)果] 手動賦值法中椎體的最大位移為28.0583mm,最大應(yīng)力為149.167N；CT灰度10分法椎體的最大位移處位移為24.3517mmm,最大應(yīng)力為148.986N。節(jié)點的位移分布情況,手動賦值法中位移活動范圍等值線較少；CT灰度10分法呈多處等值線。根據(jù)路徑圖可以看出.兩種方法運算結(jié)果存在顯著性差異。直接賦值法較灰度賦值法應(yīng)力情況總體偏低,其中皮質(zhì)骨部分應(yīng)力顯著偏大,松質(zhì)骨部分應(yīng)力明顯偏小。 [結(jié)論] 手動賦值法的應(yīng)力分布數(shù)據(jù)在皮質(zhì)骨和松質(zhì)骨之間分布相對離散,CT灰度值賦值法的應(yīng)力分布數(shù)據(jù)分布相對集中。相比較而言灰度賦值法10分法其分法更貼近于人骨復(fù)雜材料屬性的狀況,尤其適用于臨床個性化快速有限元建模。
[Abstract]:Background:
The concept of digital medicine has promoted the combination of finite element technology and medicine. The extensive application of CT data set in 3D reconstruction has accelerated the development of this process, especially in the construction of bone model. The three-dimensional finite element model can be used to analyze the stress and strain of normal bone, and can also be used to analyze it. The risk factor of fracture or the micromovement of internal fixation. In foreign countries, O'Reilly and Whyn, Little et al, Schileo et al, Yosibash and other parts of the spine and femur have been studied. The research on the finite element in China is gradually deepened, especially the concept of digital medicine is put forward by the finite element technology and the medical prescription. Many scholars have made corresponding research in the field of finite element simulation.
Finite element modeling refers to the establishment of a digital model that can be successfully calculated by a computer. The model is consistent with the mechanical properties of the physical model in reality. The essence of this model is to establish a digital model in the virtual environment of the computer by the finite element method. The model has the following requirements: first, to ensure the integrity of the mechanics; two: to The validity of the calculation is guaranteed. That is, the established finite element model has two missions to carry the complete mechanical information to ensure that the computer can calculate quickly and accurately. In the process of establishing the finite element model, we should not only ensure that the shape of the model is similar to the reality, but also the performance of some mechanical materials and the real situation of the model. The high characteristic.CT scanning that CT scan can reflect the bone model can be used as a non invasive diagnostic method of clinical routine in vitro. It can not only provide accurate geometry information of bone, but also provide bone related mechanical properties. At this stage, the most important use of CT data in the finite element field is at the present stage. The construction of three-dimensional model of bone, and another important part of the construction of finite element model: material attribute assignment, but little involved. Bone is one of the main objects of medical finite element analysis, the material properties of human bone are more complex, individual differences are obvious, there are differences between different people or different parts of the same human body. The traditional method of dividing the properties of bone materials is to assign the bone to two parts of the cortical bone and the cancellous bone, which is incompatible with the complexity of the human bone material property, and there will be great errors in the calculation. With the deepening of the understanding of the CT data and the development and application of the corresponding software, a class of software developed gradually. Such as MIMICS, BONEMAT, AMAB and so on, these software can combine the CT data as an internal data code and the finite element simulation model. The allocation scheme is based on the gray value of the CT data to determine the material properties of the finite element model. The specific method is to extract the pixel values of all the CT images in the single volume and calculate it. The average value is assigned to the cell. This method can finally achieve the purpose of determining the elastic modulus of each element in the finite element model through the CT gray value.
3D reconstruction and visualization of medical images is a theory that uses computer graphics, image processing, computer vision and human-computer interaction technology to convert medical image data into graphics or images on screen and interact with each other. Method and technology.MIMICS is an interactive medicine developed by Materialise company. The Materialise's interactive medical image control system is a highly integrated and easy to use 3D image generation and editing processing software. It can input various medical images (CT, MRI) data, establish 3D model for editing, and transform the large-scale data into the PC machine. This software can be used in addition to the application of the software. In building the 3D model, we can connect the CT gray value with the material properties of the model, and assign the material properties of the model according to a certain partition gradient. A better assignment method and a better allocation scheme can improve the error caused by individual difference in the calculation. This experiment is based on the MIMICS software. On the premise of better geometric reconstruction, the modulus of elasticity of the model is assigned by its material attribute allocation module, and the results of the finite element analysis of these models are compared, and a better assignment method is obtained by comparing it with the finite element method of the manual assignment method. Two kinds of assignment methods (CT gray value assignment method, manual assignment method) and the influence of different gradient changes on the finite element analysis results in the CT gray value assignment method, a relative economic and accurate division gradient is obtained, which provides the relevant theoretical basis for the application of the method in the finite element study, especially in the rapid modeling and analysis of clinical phase.
Finite element modeling of vertebrae
This part mainly summarizes the early modeling work of the implementation of the subject, expounds the related methods and techniques, and illustrates the whole process of effective modeling in this experiment. Finite element analysis is an important experimental means to simulate the function of human structure and mechanics in the field of biomechanics in recent years. The finite element model is the basis of the finite element simulation analysis. The aim of this model is to provide a physical framework for further finite element analysis, and then the frame can be applied to this frame. In this part, the general flow technique method and attention for the establishment of the corresponding skeleton finite element model are illustrated by the example of the thoracic and lumbar specimens. The process of constructing the geometric model in the three-dimensional reconstruction is emphasized, and the corresponding Remesh operation is used to improve the process. The method of limiting the success rate and quality of mesh generation and the method of obtaining the ideal finite element model by using Geomagic software to process the corresponding three-dimensional model.
Effect of gradient of material property distribution on mechanical properties of finite element model of vertebrae in automatic allocation method
[Objective]
The effects of different material property distribution gradients based on gray value on mechanical properties of vertebral finite element models were studied.
[method]
A healthy adult spinal column (T12 ~ L5 segment) was scanned by fast CT thin layer, and each vertebra was reconstructed in MIMICS. After Geomagic software, the mesh was introduced into ANSYS and then returned to MIMICS to distribute the material properties according to the 8 gradients such as 2,4,8,10,50100200400, and finally reimported the ANSYS software. The finite element analysis is carried out according to the same load condition.
[results]
Compared with other distribution gradients, there is a significant difference in stress between the three distribution gradients of 2,4400 (P0.05), but the results of the 8,10,50100200 gradient have little deviation.
[Conclusion]
The material attributes of the finite element model should not be too much or too little. The 10 partition gradient can not only ensure the accuracy of the calculation results, but also improve the computing speed. It is especially suitable for the personalized rapid finite element modeling of clinical personalization.
Effects of manual distribution and automatic allocation of material properties on mechanical properties of finite element models of vertebrae
[Objective]
The influence of automatic allocation method and manual assignment method on the mechanical properties of the finite element model of vertebrae is studied.
[method]
A healthy adult spinal column (T12-L5) was scanned by fast CT thin layer, and each vertebra was reconstructed in MIMICS. Remesh treatment was carried out in MIMICS through Geomagic software, and then transferred into ANSYS to mesh. The material attributes were divided according to two methods: first, manual assignment method, directly selecting peripheral single in ANSYS. The element gives the cortical bone attribute, the other units give the cancellous bone property; two, the CT gray value assignment method (automatic distribution method), the model is guided back to the MIMICS to assign the material attribute according to the distribution gradient of 10 parts. Finally, the finite element analysis is carried out in the ANSYS.
[results]
The maximum displacement of the vertebral body in the manual assignment method is 28.0583mm, the maximum stress is 149.167N, the maximum displacement of the CT gray 10 point method is 24.3517mmm, the maximum stress is the displacement distribution of the 148.986N. node, the displacement range contour line is less in the manual assignment method, and the CT grey degree method has multiple contour lines. We can see that there are significant differences in the results of the two methods. The stress in the direct assignment method is generally lower than that of the gray value method. The partial stress of the cortical bone is significantly larger and the partial stress of the cancellous bone is obviously smaller.
[Conclusion]
The distribution of stress distribution in the manual assignment method is relatively discrete between the cortical bone and the cancellous bone, and the distribution of the stress distribution data of the CT gray value assignment method is relatively concentrated. In comparison with the gray value method, the 10 division method is more close to the state of the human bone complex material properties, especially for the personalized rapid finite element modeling of clinical individualization.
【學(xué)位授予單位】：南方醫(yī)科大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2013
【分類號】：R318.08

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