||Anatomy-Based Force Model for Predicting Facial Morphological Change
||Institute of Biomedical Engineering
soft tissue change prediction
finite elements method
電腦輔助顏面變化預測系統可以協助醫師預視病患治療後的顏面外觀，同時也可以增進醫病溝通說明，本研究是以本實驗室過去所發展的顏面變化預測系統為基礎，加以研究改進，以提高顏面變化預視的準確度。本研究增加顏面肌肉模型，從電腦斷層資料建立通用頭顱模型及建立非均勻網格模型；臉部可變形模組則是應用節點施力法與有限元素法整合而成，透過節點施力法可以提供每個節點相對應的力量，而節點間則使用彈簧參數，建立骨骼模型和人臉外廓間非均勻關係；有限元素法則提供一連續且平滑的形變方式來計算顎骨位移時，顏面外廓模型所產生的形變量，最後使用三維繪圖函式庫(OpenGL)來呈現立體顏面變化的情形。比較臨床病患經正顎手術後與系統產生的顏面變化預視結果顏面的側面輪廓圖，分析臨床量化顏面軟組織變化的四個參數(FCA、NFCA、LL-LE、LL-E)，探討顏面變化預視的準確性。從實驗結果顯示，FCA相差4.89度，NFCA相差1.28度，LL-LE相差0.3 mm，和LL-E相差0.33 mm，因此改良後的系統在顏面預視方面確實較原系統更加準確，顏面變化預視結果也更符合實際病患術後的臉形。
Computer-aided system for predicting the facial changes can help the clinician to preview the face of the patient after surgical procedure. It may also facilitate the communication between the orthodontists and patients. In this study, it is to improve the accuracy of the facial change predicting system previously developed in our lab. A facial musculature model built from the CT image data with non-uniform mesh is developed for the generic model. The nodal loading force and finite element method are applied to integrate in the deformable face model. Thus, the force is applied rough the nodes, and the spring stiffness is set between neighboring nodes. The internal bone model and surface muscle model is then correlated in non-linear relationship. The finite element method is employed to provide the continuous and smooth deformation for computing the displacement of mandible. The resulting facial changes in three-dimension are obtained and previewed using OpenGL software. Comparing the actual facial profiles for the patient after treatment and predicted using proposed system with four parameters (FCA、NFCA、LL-LE、LL-E), the accuracy are analyzed. From experimental results of one case, the errors for FCA is 4.89 degree, NFCA 1.28 degree, LL-LE 0.3 mm, and LL-E 0.33 mm, respectively. It is demonstrated that the proposed system is improved in accuracy of facial change prediction, and the resulting facial profile is also very matching to the patient.
LIST OF TABLES V
LIST OF FIGURES VI
Chapter 1 INTRODUCTION 1
1.1 Background 1
1.2 Literature Review 3
1.3 Motivation 5
1.4 Purposes 6
1.5 The Organization of Thesis 6
Chapter 2 METHODS 8
2.1 System Description 8
2.2 A Generic 3D Head Model Reconstruction 10
2.3 Finite Element Method Based Deformable Facial Model 14
Chapter 3 RESULTS AND DISCUSSIONS 39
3.1 Case Application 39
3.2 Generic Head Model Improvement 41
3.3 Muscle Modification 47
3.4 The Verification for Orthognathic Surgical Simulation 48
3.5 Prediction of the 3D Facial Changes 56
3.6 Quantitative Interface for Clinical Verification 59
3.7 Discussion 63
Chapter 4 CONCLUSION AND PROSPECTS 67
4.1 Conclusion 67
4.2 Prospects 70
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