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目的建立患者口腔每颗牙齿独立的3维模型对于计算机口腔修复的精确定位和量化评估具有十分重要的意义。针对口腔CT图像序列的牙齿形态变化和排列特点,提出一种新颖的基于水平集活动轮廓模型的3维牙齿重建方法。方法基于层间映射机制,对不同部位牙层切片采用不同的分割模型:利用先验形状约束能量、基于Flux模型的边缘梯度能量、基于先验灰度的局部区域能量相结合构造的单相混合水平集模型分割牙根层切片轮廓;利用结合区域竞争约束的双相混合水平集模型分割牙冠层切片轮廓;最后利用这些层间轮廓重建出牙齿3维模型。结果对不同位置的牙齿CT图像进行分割实验,结果表明,与现有的方法相比,本文方法具有较好的分割效果和较高的准确率,平均分割相似系数达到96%。结论本文的混合水平集模型能有效克服牙髓腔和牙槽骨的干扰以及图像灰度不均匀等问题,较准确地重建出每颗牙齿独立的3维模型,从而为制定口腔修复规划、生物力学分析等奠定坚实的基础。
Objective To establish an independent 3-D model of each tooth in a patient’s oral cavity is of great significance for the accurate localization and quantitative assessment of a computer oral repair. According to the morphological changes and arrangement of dental CT images, a novel 3D reconstruction method based on level set active contour model is proposed. Methods Based on the layer-to-layer mapping mechanism, different segmentation models were applied to different sections of tooth stratum: single-phase mixing based on prior shape constraint energy, edge gradient energy based on Flux model and local region energy based on prior grayscale The level set model was used to segment the root canal slice contour. The two-phase mixed level set model was used to separate the canopy slice contour. Finally, the three-dimensional model of the tooth was reconstructed using these two layer contour. Results The CT images of different positions were segmented experimentally. The results show that compared with the existing methods, this method has better segmentation results and higher accuracy, and the average segmentation similarity coefficient reaches 96%. Conclusion The mixed-level model in this paper can effectively overcome the problems of pulp cavity and alveolar bone interference and uneven grayscale of images, so as to reconstruct the three-dimensional model of each tooth accurately. Therefore, Mechanical analysis and lay a solid foundation.