Accuracy and reliability of 3D stereophotogrammetry: A comparison to direct anthropometry and 2D photogrammetry

Objective:To evaluate the accuracy of three-dimensional (3D) stereophotogrammetry by comparing it with the direct anthropometry and digital photogrammetry methods. The reliability of 3D stereophotogrammetry was also examined.Materials and Methods:Six profile and four frontal parameters were directly measured on the faces of 80 participants. The same measurements were repeated using two-dimensional (2D) photogrammetry and 3D stereophotogrammetry (3dMDflex System, 3dMD, Atlanta, Ga) to obtain images of the subjects. Another observer made the same measurements for images obtained with 3D stereophotogrammetry, and interobserver reproducibility was evaluated for 3D images. Both observers remeasured the 3D images 1 month later, and intraobserver reproducibility was evaluated. Statistical analysis was conducted using the paired samples t-test, intraclass correlation coefficient, and Bland-Altman limits of agreement.Results:The highest mean difference was 0.30 mm between direct measurement and photogrammetry, 0.21 mm between direct measurement and 3D stereophotogrammetry, and 0.5 mm between photogrammetry and 3D stereophotogrammetry. The lowest agreement value was 0.965 in the Sn-Pro parameter between the photogrammetry and 3D stereophotogrammetry methods. Agreement between the two observers varied from 0.90 (Ch-Ch) to 0.99 (Sn-Me) in linear measurements. For intraobserver agreement, the highest difference between means was 0.33 for observer 1 and 1.42 mm for observer 2.Conclusions:Measurements obtained using 3D stereophotogrammetry indicate that it may be an accurate and reliable imaging method for use in orthodontics.     

Three-dimensional superimposition for patients with facial palsy: an innovative method for assessing the success of facial reanimation procedures

Facial palsy is a severe condition that may be ameliorated by facial reanimation, but there is no consensus about how to judge its success. In this study we aimed to test a new method for assessing facial movements based on 3-dimensional analysis of the facial surfaces. Eleven patients aged between 42 and 77 years who had recently been affected by facial palsy (onset between 6 and 18 months) were treated by an operation based on triple innervation: the masseteric to temporofacial nerve branch, 30% of the hypoglossal fibres to the cervicofacial nerve branch, and the contralateral facial nerve through two cross-face sural nerve grafts. Each patient had five stereophotogrammetric scans: at rest, smiling on the healthy side (facial stimulus), biting (masseteric stimulus), moving the tongue (hypoglossal stimulus), and corner-of-the-mouth smile (Mona Lisa). Each scan was superimposed onto the facial model of the “rest” position, and the point-to-point root mean square (RMS) value was automatically calculated on both the paralysed and the healthy side, together with an index of asymmetry. One-way and two-way ANOVA tests, respectively, were applied to verify the significance of possible differences in the RMS and asymmetry index according to the type of stimulus (p = 0.0329) and side (p < 0.0001). RMS differed significantly according to side between the facial stimulus and the masseteric one on the paralysed side (p = 0.0316). Facial stimulus evoked the most asymmetrical movement, whereas the masseteric produced the most symmetrical expression. The method can be used for assessing facial movements after facial reanimation.     

Precision and accuracy assessment of single and multicamera three-dimensional photogrammetry compared with direct anthropometry

ObjectivesTo assess the precision and accuracy of single-camera photogrammetry (SCP) and multicamera photogrammetry (MCP) compared with direct anthropometry (DA).Materials and MethodsA total of 30 participants were recruited, and 17 soft tissue landmarks were identified and used to complete a total of 16 measurements. Using SCP and MCP, two three-dimensional (3D) images were acquired from each participant. All 3D measurements and direct measurements were measured twice by the same operator to assess intraexaminer repeatability. Intraclass coefficients (ICCs) were used to evaluate intraexaminer repeatability and interexaminer agreement of the methods. Nonparametric bootstrap analyses were used to compare the means of the measurements among the three methods.ResultsAll three methods showed excellent intraexaminer repeatability (ICCs > 0.90), except interpupillary distance (ICC = 0.86) measured by SCP. Both SCP and MCP showed excellent interexaminer agreement (ICCs > 0.90), except interpupillary distance (ICC = 0.79), left gonion-pogonion (ICC = 0.74), and columella-subnasale-labrale superior angle (ICC = 0.86) measured by SCP. Overall, there was good agreement between methods, except for columella-subnasale-labrale superior angle (ICC = 0.40) between SCP and MCP.ConclusionsBoth SCP and MCP techniques were found to be reliable and valid options for 3D facial imaging. SCP produced slightly larger mean values for several measurements, but the differences were within a clinically acceptable range. Because of the larger margin of errors, measurements including the gonial area and subnasale should be assessed with caution.     

Evaluation of a portable low-budget three-dimensional stereophotogrammetry system for nasal analysis

Background

Three-dimensional (3D) photogrammetry has reached high standards and accuracy but is mainly conducted with stationary and expensive systems. The purpose of this study was to evaluate the accuracy of a low-budget portable system with special regard to the gracile and challenging nasal region.

三维面部影像在面部软组织不对称研究中的进展

面部美学是口腔医学关注的重点内容,而面部软组织对称性是影响面部美学的重要因素,近年来随着三维面部扫描技术及相关软件的发展,使得客观准确地评价面部软组织不对称性成为可能,相较于CBCT技术而言,该法更为便捷且无需担心辐射对患者的影响,因此在临床应用中有比较大的潜力。本文回顾了近年来利用三维面部影像分析面部不对称性的相关研究,梳理了该领域的发展方向以及具体的应用领域。     

三维面部影像在面部软组织不对称研究中的进展

面部美学是口腔医学关注的重点内容,而面部软组织对称性是影响面部美学的重要因素,近年来随着三维面部扫描技术及相关软件的发展,使得客观准确地评价面部软组织不对称性成为可能,相较于CBCT技术而言,该法更为便捷且无需担心辐射对患者的影响,因此在临床应用中有比较大的潜力。本文回顾了近年来利用三维面部影像分析面部不对称性的相关研究,梳理了该领域的发展方向以及具体的应用领域。     

Reliability and validity of measurements of facial swelling with a stereophotogrammetry optical three-dimensional scanner

Volume changes in facial morphology can be assessed using the 3dMD DSP400® stereo-optical 3-dimensional scanner, which uses visible light and has a short scanning time. Its reliability and validity have not to our knowledge been investigated for the assessment of facial swelling. Our aim therefore was to assess them for measuring changes in facial contour, in vivo and in vitro. Twenty-four healthy volunteers with and without an artificial swelling of the cheek were scanned, twice in the morning and twice in the afternoon (in vivo measurements). A mannequin head was scanned 4 times with and without various externally applied artificial swellings (in vitro measurements). The changes in facial contour caused by the artificial swelling were measured as the change in volume of the cheek (with and without artificial swelling in place) using 3dMD Vultus® software. In vivo and in vitro reliability expressed in intraclass correlations were 0.89 and 0.99, respectively. In vivo and in vitro repeatability coefficients were 5.9 and 1.3 ml, respectively. The scanner underestimated the volume by 1.2 ml (95% CI -0.9 to 3.4) in vivo and 0.2 ml (95% CI 0.02 to 0.4) in vitro.     

Reproducibility of the dynamics of facial expressions in unilateral facial palsy

The aim of this study was to assess the reproducibility of non-verbal facial expressions in unilateral facial paralysis using dynamic four-dimensional (4D) imaging. The Di4D system was used to record five facial expressions of 20 adult patients. The system captured 60 three-dimensional (3D) images per second; each facial expression took 3–4 seconds which was recorded in real time. Thus a set of 180 3D facial images was generated for each expression. The procedure was repeated after 30 min to assess the reproducibility of the expressions. A mathematical facial mesh consisting of thousands of quasi-point ‘vertices’ was conformed to the face in order to determine the morphological characteristics in a comprehensive manner. The vertices were tracked throughout the sequence of the 180 images. Five key 3D facial frames from each sequence of images were analyzed. Comparisons were made between the first and second capture of each facial expression to assess the reproducibility of facial movements. Corresponding images were aligned using partial Procrustes analysis, and the root mean square distance between them was calculated and analyzed statistically (paired Student t-test, P < 0.05). Facial expressions of lip purse, cheek puff, and raising of eyebrows were reproducible. Facial expressions of maximum smile and forceful eye closure were not reproducible. The limited coordination of various groups of facial muscles contributed to the lack of reproducibility of these facial expressions. 4D imaging is a useful clinical tool for the assessment of facial expressions.     

三维立体摄影技术在颜面部软组织中的应用

颜面部软组织三维图像信息的获取方法有莫尔云纹、激光扫描和三维立体摄影测量.莫尔条纹法具有成本低、非介入性等优点,但其面部重建还是不够直观且灵敏度较低.激光扫描精度高,立体重构快捷逼真;但其易伤害眼睛,只捕捉表面形貌,无法观察软组织质地;数据采集时间较长,易增加运动伪影.三维立体摄影测量为非介入性的,安全无创;拍摄迅速,图像采集时间短,无运动伪影的风险;数据存储方便,查询快捷,可对归档的图像进行后续的反复分析;提高了测量速度和精度;与被检查对象无接触;医师与患者间的沟通更加便捷,有利于医师设计和调整更符合患者要求的个体化治疗方案.三维立体摄影测量也令今后正畸和正颌专家的远程网上诊疗成为可能,有可能成为口腔颜面部修复重建的常规检查项目.     

Comparison of facial morphologies between adult Chinese and Houstonian Caucasian populations using three-dimensional imaging

The objective of this study was to compare the facial morphologies of an adult Chinese population to a Houstonian white population. Three-dimensional (3D) images were acquired via a commercially available stereophotogrammetric camera system, 3dMDface?. Using the system, 100 subjects from a Houstonian population and 71 subjects from a Chinese population were photographed. A complex mathematical algorithm was performed to generate a composite facial average (one for males and one for females) for each subgroup. The computer-generated facial averages were then superimposed based on a previously validated superimposition method. The facial averages were evaluated for differences. Distinct facial differences were evident between the subgroups evaluated. These areas included the nasal tip, the peri-orbital area, the malar process, the labial region, the forehead, and the chin. Overall, the mean facial difference between the Chinese and Houstonian female averages was 2.73 ± 2.20 mm, while the difference between the Chinese and Houstonian males was 2.83 ± 2.20 mm. The percent similarity for the female population pairings and male population pairings were 10.45% and 12.13%, respectively. The average adult Chinese and Houstonian faces possess distinct differences. Different populations and ethnicities have different facial features and averages that should be considered in the planning of treatment.     

激光扫描在面部畸形三维重建及测量中的初步应用

目的开发建立一套面部三维结构重建、测量及诊断分析系统。方法应用系统建立标准石膏立方体试件以及石膏头像三维计算机模型并进行定点、测量,测量值与标准值比较获得系统建模误差以及定点误差范围;2例面部畸形患者进行了面部三维扫描建模,应用系统对患者面部计算机模型进行了定点、线距、角度测量以及初步对称性分析。结果三维计算机模型的建模误差在0.2 mm以内,定点误差在0.5 mm以内。应用本系统可以完成三维计算机模型的定点、线距、角度测量及对称性分析工作,基本能够达到临床要求。结论三维激光扫描技术为颌面部畸形患者面部软组织三维结构重建和非接触式测量提供了一种简便、精确、高效的方法。     

Three-dimensional facial volume analysis using algorithm-based personalized aesthetic templates

Three-dimensional stereophotogrammetry is commonly used to assess volumetric changes after facial procedures. A lack of clear landmarks in aesthetic regions complicates the reproduction of selected areas in sequential images. A three-dimensional volumetric analysis was developed based on a personalized aesthetic template. The accuracy and reproducibility of this method were assessed. Six female volunteers were photographed using the 3dMDtrio system according to a clinical protocol, twice at baseline (T1) and twice after 1 year (T2). A styrofoam head was used as control. A standardized aesthetic template was morphed over the baseline images of the volunteers using a coherent point drift algorithm. The resulting personalized template was projected over all sequential images to assess surface area differences, volume differences, and root mean square errors. In 12 well-defined aesthetic areas, mean average surface area and volume differences between the two T1 images ranged from −7.6 mm² to 10.1 mm² and −0.11 cm³ to 0.13 cm³, respectively. T1 root mean square errors ranged between 0.24 mm and 0.62 mm (standard deviation 0.18–0.73 mm). Comparable differences were found between the T2 images. An increase in volume between T1 and T2 was only observed for volunteers who gained in body weight. Personalized aesthetic templates are an accurate and reproducible method to assess changes in aesthetic areas.     

2种三维颜面部扫描仪测量精度的定量评价

目的：对三维颜面部扫描仪进行真人实际测量精度评价。方法：分别应用三维颜面部扫描仪3dMD 和 FaceScan 获取10名正常面型志愿者的三维面相数字模型,测量每个模型上的10个特征线段长度和5个特征角度,并分别与高精度线激光扫描仪（Faro）获取的参考值进行统计学分析和测量学分析,计算面貌特征测量误差与实际测量精度。结果：3dMD 和 FaceS-can 对正常面型人群的长度测量精度分别为（－0．37±0．68）mm 和（－0．29±0．53）mm（P ＝0．223）,角度测量精度分别为（－0．22±2．14）°和（0．12±2．69）°（P ＝0．428）。结论：2种三维面部扫描仪获取的三维面相数据无显著差异。     

Three-dimensional stereophotogrammetry measurement of facial asymmetry in patients with congenital muscular torticollis: a non-invasive method

The aim of this study was to evaluate three-dimensional (3D) stereophotogrammetry based methods for measuring craniofacial asymmetry in patients with congenital muscular torticollis (CMT). This study focused on the differences in craniofacial asymmetry in CMT patients compared with a healthy control group using 3D photographs. The difference in facial asymmetry between the CMT group and control group was measured using two methods to analyse facial asymmetry in distinct anatomical regions: (1) mirroring and surface-based registration to analyse the overall facial asymmetry; (2) the ‘coherent point drift’ based method. Thirty-one patients with CMT and 84 controls were included in the study. A statistically significant difference was found between the CMT patients and a healthy control group. The measured facial asymmetry for the CMT group was 1.71 ± 0.66 mm and for the controls 0.46 ± 0.14 mm (P < 0.05). A significant difference was found in surface ratio for the cheek, nose and the forehead region (P < 0.05). With its minimal invasive character, 3D stereophotogrammetry is a useful tool in measuring the facial asymmetry associated with CMT and to quantify the treatment-induced facial changes. In the future 3D facial data could be used to create a ranking-scale to categorize the severity of facial asymmetry.     

二维及三维摄影应用于单侧唇裂患者面部测量的精确性比较

目的比较二维摄影与三维摄影应用于分析唇腭裂患儿不对称面貌的精确性,以及不对称畸形严重程度对面部测量精确性的影响,以指导临床测量工作。方法前瞻性纳入单侧唇裂患儿。分别拍摄二维和三维照片,对裂隙侧与非裂隙侧鼻尖偏移、鼻小柱基部偏移、人中切迹偏移、唇高比值、鼻小柱高度比值、鼻底宽度比值、侧唇长比值等7个指标进行测量,以游标卡尺面部直接测量为金标准。以裂隙侧/非裂隙侧比值表示畸形程度,以二维或三维摄影比值结果同直接测量的比值之差表示误差大小。结果最终纳入患者13例。与实际测量相比,二维摄影系统对唇高比值的测量结果偏大(P=0.019),对鼻小柱高度比值的测量结果偏小(P=0.008);三维摄影系统对鼻底宽度比值的测量结果偏小(P=0.003);二维摄影的鼻尖偏移(P=0.022)、三维摄影的人中切迹偏移(P=0.025)、侧唇长比值(P=0.036)的测量误差大小与畸形程度成显著负相关。结论二维摄影与三维摄影体系均存在夸大或缩小畸形程度的误差偏倚,且部分测量误差可能随畸形程度减小而增大。在应用二维摄影和三维摄影分析唇腭裂畸形时需考虑这些偏倚,以期更客观地进行面容评价。     

Esthetic evaluation of facial cheek volume: A study using 3D stereophotogrammetry

Objectives:To investigate the influence of cheek volume on facial esthetics judged by orthodontists and non-specialists.Materials and Methods:A 25-year-old female''s natural and smiling face was captured by 3D stereophotogrammetry. Cheek volume of the 3D image was altered to different degrees three-dimensionally. For the natural and smiling face, seven groups of facial images were created: decreased grade I/II/III, increased grade I/II/III, and the original one. Thirty orthodontists and 30 nonspecialists were invited to perform esthetic evaluation of the original and transformed images using a questionnaire. Data were calculated with one-way analysis of variance (least significant difference test) and independent samples t test.Results:Compared to nonspecialists, orthodontists gave lower esthetic scores to the decreased grade III facial images (maximum deformation degree: 7.500 mm and 7.327 mm in natural and smiling face-oriented image groups, respectively). The decreased grade III facial images also received the highest age ranks. However, the increased grade III facial images received the lowest scores and highest age ranks from nonspecialists (maximum deformation degree: 6.994 mm and 5.300 mm in natural and smiling face-oriented image groups, respectively) (P < .01).Conclusions:Orthodontists and nonspecialists showed different esthetic evaluation of varied cheek volume. The influence of cheek volume in orthodontic diagnostic analysis needs further consideration.     

Development of three-dimensional facial expression models using morphing methods for fabricating facial prostheses

Purpose

It is essential to fabricate a best-fit three-dimensional (3D) facial prosthesis model capable of facial expressions. In order for the facial prosthesis to remain in position, especially around marginal areas subject to movement, a new method of making 3D facial expression models using time-series data allowing changes in facial expression by morphing technique was developed.

Validation and reproducibility of a high-resolution three-dimensional facial imaging system

OBJECTIVE: To assess the accuracy and reproducibility of a high-resolution three-dimensional imaging system (Di3D). DESIGN: The three-dimensional imaging system was validated in vitro using 12 adult facial plaster casts, which had landmarks marked, and the positions of the landmarks on the three-dimensional images captured by Di3D were compared with those obtained by a coordinate measuring machine (CMM). METHODS: Operator error was measured by repeatedly locating landmarks on the three-dimensional image. Reproducibility error of the images was calculated by capturing three-dimensional images of the facial casts on two separate occasions; the Euclidean distance between the two matched sets of coordinates was then calculated. The Di3D system error was assessed by calculating the three-dimensional global positions of landmarks on the three-dimensional images and comparing them with those obtained by CMM (gold standard). RESULTS: The operator error in placement of landmarks on the three-dimensional model was 0.07mm, range 0.02-0.11mm. The reproducibility of the Di3D capture was 0.13mm, range 0.11-0.14mm. The mean distance between the CMM and Di3D landmarks, which constitutes the Di3D system error, was an average of 0.21mm, range 0.14-0.32mm. CONCLUSIONS: The Di3D system error was within 0.2mm, which is clinically acceptable, and offers considerable improvement in stereophotogrammetry for facial capture and analysis.