M. Bock

Validation of a Vision-Based, Three-Dimensional Facial Imaging System

Objective The aim of this study was to assess the accuracy of a newly developed three-dimensional (3D) imaging system in recording facial morphology. Methods Twenty-one infants with cleft lip each had a full-face alginate impression taken at the time of primary lip repair, and a stone cast was constructed from each impression. Five anthropometric points were marked on each cast. Each cast was digitized, and the 3D co-ordinates of the five points were obtained using a co-ordinate measuring machine (CMM, Ferranti) of documented accuracy (9.53 μm). Each cast was scanned in four positions using a computerized stereophotogrammetry (C3D) system. The five points were located on the 3D images, and their 3D co-ordinates were extracted by three operators. The co-ordinate systems produced by C3D were aligned, via translation and rotation, to match the CMM co-ordinate system using partial ordinary procrustes analysis. The displacements of the adjusted C3D co-ordinates from the reference co-ordinates were then measured. Three different types of errors were identified: operator, system, and registration errors. Results Operator error was within 0.2 mm of the true co-ordinates of the landmarks. C3D was accurate within 0.4 mm. The average displacement of points over the 21 casts at four positions for the three operators was 0.79 mm (median 0.68). Conclusions The presented 3D imaging system is reliable in recording facial deformity and could be utilized in recording cleft deformities and measuring the changes following surgery

An appraisal of three methods of rating facial deformity in patients with repaired complete unilateral cleft lip and palate.

OBJECTIVES To evaluate the reliability of clinical assessment, two-dimensional color transparencies and three-dimensional imaging for evaluating the residual facial deformity in patients with repaired complete unilateral cleft lip and palate (UCLP) and compare the ratings of facial deformity made by health care professionals with those made by lay assessors. PATIENTS AND PARTICIPANTS Thirty-one randomly selected subjects aged 10 to 30 years with repaired complete UCLP. Five professionals and five laypersons evaluated each subjects residual cleft-related facial deformity using clinical assessment, two-dimensional color transparencies, and three-dimensional images. MAIN OUTCOME MEASURES The facial deformity of the full face, lip, nose, and midface were scored using a 5-point ordinal scale on two occasions with a 1-month interval. Intra- and interexaminer agreements were calculated from weighted kappa statistics. Bootstrap permutation tests were used to detect any differences in agreement. RESULTS Assessment of facial deformity showed good reproducibility across the three assessment media (kappa = 0.42 to 0.83, SE 0.08). Clinical assessment among lay assessors, however, was poor to moderate (kappa = 0.16 to 0.58, SE 0.07). For all assessors, there was no difference in the two nonclinical media relative to the standard clinical assessment for assessments of the full face (p =.377). For assessments of the lip or nose, transparency scores were in greater agreement with the clinical scores than were the three-dimensional assessment scores (p =.017 and.011, respectively). For rating the midface, the three-dimensional scores were in greater agreement with the clinical scores than were the color transparencies scores (p =.047). CONCLUSIONS In comparison with lay assessors, clinical assessment among professionals was more reproducible. This was not so for nonclinical media. The equivalence of using the color transparencies and three-dimensional media relative to the clinical assessment depends on the region of the face being considered.

Are Facial Expressions Reproducible

OBJECTIVES To determine the extent of reproducibility of five facial expressions. DESIGN Thirty healthy Caucasian volunteers (15 males, 15 females) aged 21 to 30 years had 20 landmarks highlighted on the face with a fine eyeliner pencil. Subjects were asked to perform a sequence of five facial expressions that were captured by a three-dimensional camera system. Each expression was repeated after 15 minutes to investigate intrasession expression reproducibility. To investigate intersession expression reproducibility, each subject returned 2 weeks after the first session. A single operator identified 3-dimensional coordinate values of each landmark. A partial ordinary procrustes analysis was used to adjust for differences in head posture between similar expressions. Statistical analysis was undertaken using analysis of variance (linear mixed effects model). RESULTS Intrasession expression reproducibility was least between cheek puffs (1.12 mm) and greatest between rest positions (0.74 mm). The reproducibility of individual landmarks was expression specific. Except for the lip purse, the reproducibility of facial expressions was not statistically different within each of the two sessions. Rest position was most reproducible, followed by lip purse, maximal smile, natural smile, and cheek puff. Subjects did not perform expressions with the same degree of symmetry on each occasion. Female subjects demonstrated significantly better reproducibility with regard to the maximal smile than males (p =.036). CONCLUSIONS Under standardized conditions, intrasession expression reproducibility was high. Variation in expression reproducibility between sessions was minimal. The extent of reproducibility is expression specific. Differences in expression reproducibility exist between males and females.

Facial characterization of infants with cleft lip and palate using a three-dimensional capture technique.

Objective To characterize the soft tissue features of infants with unilateral cleft lip (UCL) and unilateral complete cleft lip and palate (UCLP) prior to primary surgery and compare with noncleft controls. Design Prospective controlled capture of the facial morphology of infants using a noninvasive three-dimensional stereophotogrammetry method. Participants 23 children with presurgical cleft: 11 UCL (M = 6, F = 5); 12 UCLP (M = 9, F = 3), and 21 noncleft controls (M = 7, F = 14) were imaged at approximately 3 months of age (range 10 to 16 weeks). Main Outcome Measure Accurate, repeatable quantification of facial soft tissues in infants with clefts prior to surgery. Results Significant differences (p < .05) were found between the UCLP group and UCL and control groups in anatomical and soft nose width, cleft-side alar wing length, and nasal tip horizontal displacement. Both cleft groups were significantly different from controls and from each other in cleft-side nostril dimensions, alar wing angulation, columella angle, and alar base to corner of mouth dimension; alar base width; and soft tissue defect in nose and the lip and philtrum length bordering the cleft. Significant differences between clefts and controls were identified in the nostril and philtrum on the noncleft side. Conclusions The use of children with UCL as controls for UCLP studies is inappropriate. This technique overcame the limitations of direct measurement of infant faces to aid the surgeon in the planning and subsequent re-evaluation of surgical rationale.

Three-dimensional facial characteristics of Caucasian infants without cleft and correlation with body measurements.

Objective The aim of this study was to characterize the soft tissue facial features of infants without cleft and to report on the correlation between these with weight, length, and head circumference. Design This was a prospective study using a noninvasive three-dimensional (3D) stereophotogrammetry (C3D) system to capture the images of the participants. Landmarks were identified on the 3D facial images. Means and SDs were derived for facial distances and angles. A facial asymmetry score was calculated for each image. Two sample Students t tests, Pearsons correlation coefficients and analysis of covariance were used to ascertain any gender differences and determine whether these could be explained by weight differences. Participants Eighty-three infants, 41 boys and 42 girls, were captured at rest with their lips apart, at approximately 3 months of age. Results Significant sex differences, of 1 to 2 mm, were found in several facial dimensions, such as face height and nose width. The larger facial measurements correlated significantly with body measurements. Analysis of variance confirmed these differences could be explained by differences in weight. There were no sex differences in the nose/mouth width ratios or in any of the angles measured, suggesting that there may be little sex difference in shape. A slight degree of asymmetry in the faces of infants without cleft was detected. Conclusions Comparisons between noncleft controls and infants with cleft should take cognizance of normal age and sex variations in height and weight that occur among infants.

Estimation and inference for error variance in bivariate nonparametric regression

In nonparametric regression, principal interest usually lies in the estimation of a smooth curve or surface defining the mean response at particular values of the co-variates. However, in order to move beyond descriptive use an estimate of the underlying error variance is required as an essential step in constructing interval estimates or comparing models. In the case of a single covariate, a variety of methods is available for estimating error variance, based on local differencing techniques. These methods are investigated in the important case of two covariates. An estimator constructed from residuals based on a nonparametric regression surface using a very small value of smoothing parameter is proposed as the most effective approach. A specific proposal based on nearest neighbour distances is investigated for choice of the smoothing parameter. Quadratic form techniques are used to construct confidence intervals and tests based on estimates of error variance. These include comparisons of error variances from different groups of data and the assessment of the assumption of constant variance across a regression surface. The techniques are illustrated on examples with real data.

Exploring Variation in Three-Dimensional Shape Data

A variety of very useful methods of statistical shape analysis are available for landmark data. In particular, standard methods of multivariate analysis can often be applied after suitable alignment and transformation of the data. An important example is the use of principal components analysis to provide a convenient route to graphical exploration of the main modes of variation in a sample. Where there are many landmarks or shape information is extracted in the form of curves or surfaces, the dimensionality of the resulting data can be very high and it is unlikely that substantial proportions of variability will be captured in one or two principal components. Issues of graphical exploration are explored in this setting, including random tours of a suitable low-dimensional subspace, the comparison of different groups of data, longitudinal changes and the identification of the features which distinguish individual cases from a group of controls. A suitable software environment for handling these methods with three-dimensional data is outlined. Issues of comparing principal components across time are also tackled through appropriately constructed permutation tests. All of these techniques are illustrated on a longitudinal study of facial development in young children, with particular interest in the identification of differences in facial shape between control children and those who have undergone surgical repair of a cleft lip and/or palate.

Data Extraction from Dense 3-D Surface Models

Stereo-photogrammetry involves the use of pairs of cameras to extend standard photographic methods by recovering depth information through triangulation (Ayoub et al. 1998). The resulting data consist of a point-cloud of three-dimensional observations, providing a digital representation of the surface of the object of interest. The number of observations can typically be many thousands, providing a rich source of information on object shape. This can be represented efficiently as an irregular triangular mesh, in Virtual Reality Modelling Language form.