手術(shù)仿真系統(tǒng)中四面體切割方法的研究.pdf

1、隨著科學(xué)可視化技術(shù)的成熟和發(fā)展,醫(yī)學(xué)成為虛擬現(xiàn)實(VR)的主要應(yīng)用領(lǐng)域之一.VR在醫(yī)學(xué)領(lǐng)域上的一類重要應(yīng)用是手術(shù)仿真系統(tǒng),就是專門用來模擬在手術(shù)過程可能遇到的各種現(xiàn)象的虛擬現(xiàn)實應(yīng)用系統(tǒng).它所涉及的內(nèi)容包括對醫(yī)學(xué)數(shù)據(jù)的交互與可視化,以及對于物體運動變化的模擬和各種感官反饋的模擬.手術(shù)仿真是一個極具挑戰(zhàn)性的研究課題,涉及諸多研究領(lǐng)域,如計算機圖形學(xué)、計算機視覺、生物力學(xué)、機器人學(xué)、醫(yī)學(xué)等等.人體軟組織及器官的切割仿真是虛擬手術(shù)仿真的重要組成

2、部分,軟組織及器官的幾何模型普遍采用四面體模型,切割的同時,軟組織及器官的拓撲結(jié)構(gòu)發(fā)生變化,模型中的部分四面體基元必須能夠通過分裂或合并以適應(yīng)上述變化,醫(yī)學(xué)數(shù)據(jù)在三維場景中的交互和可視化是手術(shù)仿真的基本要求,因此,第二章"四面體重構(gòu)"以及第三章"四面體單元穩(wěn)定性"是該文重點討論的兩個部分.該論文主要研究以下兩個方面的工作:1)四面體重構(gòu)針對部分切割四面體和完全切割四面體拓撲結(jié)構(gòu)的不同,該文提出了采用對部分切割的四面體和完全切割的四面體分

3、別采用不同的方法來進行四面體重構(gòu).對部分切割四面體采取無縫切割法,對完全切割的四面體采用最小子集法分別進行處理,在減小新生成的四面體的數(shù)量上和處理的復(fù)雜性上做一個折衷.2)四面體單元穩(wěn)定性的提高四面體重構(gòu)后新產(chǎn)生的單元的數(shù)量和質(zhì)量將直接影響到模型后續(xù)計算.整個模型的穩(wěn)定性取決于單個四面體的穩(wěn)定性,如果某個四面體不穩(wěn)定,將會造成整個模型的不穩(wěn)定.該文引入了兩種單元質(zhì)量的描述方法,簡單介紹了已有的提高四面體穩(wěn)定性方法之一—投射法;然后介紹了

4、Delaunay方法中使用較廣泛的逐點插入法的核心思想,將Delaunay網(wǎng)格構(gòu)造法中處理退化單元的方法:刪除法和換面法,改造后應(yīng)用于四面體穩(wěn)定性的提高上.試驗結(jié)果表明:此法在一定程度上避免了狹長單元和扁平單元的產(chǎn)生.關(guān)鍵詞:手術(shù)仿真,規(guī)整法,無縫切割法,最小數(shù)據(jù)集法,投射法,Delaunay方法.AbstractMedicine is becoming one of the major application fields for V

5、irtualReality (VR), due to rapid development of Scientific Visualization in recentyears.Surgery Simulation System is a medical Virtual Reality systemdedicated to simulating the dynamic process in surgery. It involves the

6、visualization of medical data (usually anatomical), interaction with thevisualized data, simulating behaviors of body deformation and feedback inmodalities of vision, sound, force, touch, and smell. VR with a medicalappl

7、ication combines research in Computer Graphics,Computer Vision, Biomechanics, Robotics and Medicine. Cutting process of soft tissue and organs is very important in virtual surgery simulation. Tetrahedron is widely used t

8、o construct the geometric model of virtual organs. Efficient methods must be developed to split or merge tetrahedrons in order to adapt to topology changes during cutting process.The main parts of this thesis are the two

9、 chapters on"Reconstruction of Tetrahedrons"and"Stability of Tetrahedrons" Main research work I have done is listed as follows: 1) Reconstruction of Tetrahedrons. Noticing the difference in constructing partially cut tet

10、rahedron and fully cut tetrahedron, we take two different approaches to reconstruct tetrahedron. The crack free method is used for partially cut tetrahedron and minimal set method is used for fully cut tetrahedron. This

11、is a reasonable compromise between reducing the number of tetrahedrons generated and complexity of reconstruction.2) Stability of Tetrahedrons.The quality and quantity of the newly generated tetrahedrons will greatly aff

12、ect the subsequent computations. The stability of the model depends on each individual tetrahedron. A single unstable tetrahedron could lead to instability of the entire model.Two waysto measure stability of tetrahedrons

13、 will be introduced. An earlier method to improve tetrahedron stability, the Snap Method, will be briefly discussed. Then techniques used in Delaunay triangulation to deal with degenerated elements will bethoroughly inve

14、stigated.These techniques,element deletion and face swapping, will be used for improving stability of tetrahedrons in this thesis.Zhang Jiping(Computer Software and Theory) Directed by Pan ZhenkuanKeywords:SurgerySimulat