Objective: To establish a novel method based on three-dimensional (3D) shape analysis and weighted Procrustes analysis (WPA) algorithm to construct a 3D facial symmetry reference plane (SRP), automatically assigning weight to facial anatomical landmarks. The WPA algorithm suitability for commonly observed clinical cases of mandibular deviation were analysed and evaluated.
Methods: Thirty patients with mandibular deviation were recruited for this study. The 3D facial SRPs were extracted independently based on original-mirror alignment method. Thirty-two anatomical landmarks were selected from the overall region by three times to obtain the mean coordinate. The SRP of experimental groups 1 and 2 were using the standard Procrustes analysis (PA) algorithm and WPA algorithm, respectively. A reference plane defined by experts based on regional iterative closest point (ICP) algorithm, served as the ground truth. Three experts manually selecting facial regions with good symmetry for original model, and common region was included in the study. The angle error values between the SRP of WPA algorithm in the experimental group 1 and the truth plane were evaluated in this study, and the SRP of PA algorithm of experimental group 2 was calculated in the same way. Statistics and measurement analysis were used to comprehensively evaluate the clinical suitability of the WPA algorithm to calculate the SRP. A paired t-test analysis (two-tailed) was conducted to compare the angles.
Results: The average angle error between the SRP of WPA algorithm and the ground truth was 1.53°±0.84°, which was smaller than that between the SRP of PA and the ground truth (2.06°±0.86°). There were significant differences in the angle errors among the groups (P < 0.05). For the patients with severe mandibular deviation that the distance between pogonion and facial midline greater than 12 mm, the average angle error of the WPA algorithm was 0.86° smaller than that of the PA algorithm.
Conclusion: The WPA algorithm, based on weighted shape analysis, can provide a more adaptable SRP than the standard PA algorithm when applied to mandibular deviation patients and preliminarily simulate the diagnosis strategies of clinical experts.
目的: 建立一种基于三维形态学分析的赋权普氏分析(weighted Procrustes analysis, WPA)方法, 实现对下颌偏斜患者面部解剖标志点不对称程度量化赋权的三维面部对称参考平面自动化构建。
方法: 临床收集下颌偏斜患者30例, 基于本体-镜像关联法的普氏分析(Procrustes analysis, PA)算法和自主研发的WPA算法, 分别构建每名患者三维面部模型的对称参考平面(实验组一和二), 以专家定义的区域迭代最近点(iterative closest point, ICP)算法(选取对称性良好的区域)构建的对称参考平面为“真值平面”, 作为参考组。以实验组与参考组的平面角度误差作为评价指标, 分别比较两个实验组与参考组的差异, 评价WPA算法构建对称参考平面的临床适用性。
结果: 30例下颌偏斜患者WPA算法构建的对称参考平面与真值平面的角度误差为1.53°±0.84°, PA算法构建的对称参考平面与真值平面的角度误差为2.06°±0.86°。对于下颌偏斜大于12 mm的患者, WPA算法比PA算法的平均平面角度误差小0.86°。
结论: 基于三维面部形态学分析的WPA算法对下颌偏斜面部不对称畸形患者构建三维面部对称参考平面的临床应用效果比传统PA算法有显著提高, 初步达到了口腔临床专家级诊断策略的效果。
Keywords: Euclidean distance matrix analysis; Facial asymmetry; Procrustes analysis; Symmetry reference plane.