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The Accuracy of Conformation of a Generic Surface Mesh for the Analysis of Facial Soft Tissue Changes.

Cheung MY, Almukhtar A, Keeling A, Hsung TC, Ju X, McDonald J, Ayoub A, Khambay BS - PLoS ONE (2016)

Bottom Line: The same six regions were selected on the aligned conformed simulated meshes and the surgical movement determined by determining the Euclidean distances and the mean absolute x, y and z distances of the mesh points making up the six regions were determined.In all cases the mean Euclidian distance between the simulated movement and conformed region was less than 0.7 mm.For the x, y and z directions the majority of differences in the mean absolute distances were less than 1.0mm except in the x-direction for the left and right cheek regions, which was above 2.0 mm.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Dentistry, University of Hong Kong, Hong Kong, China.

ABSTRACT

Purpose: Three dimensional analysis of the face is required for the assessment of complex changes following surgery, pathological conditions and to monitor facial growth. The most suitable method may be "dense surface correspondence".

Materials and methods: This method utilizes a generic facial mesh and "conformation process" to establish anatomical correspondences between two facial images. The aim of this study was to validate the use of conformed meshes to measure simulated maxillary and mandibular surgical movements. The "simulation" was performed by deforming the actual soft tissues of the participant during image acquisition. The study was conducted on 20 volunteers and used 77 facial landmarks pre-marked over six anatomical regions; left cheek, right cheek, left upper lip, philtrum, right upper lip and chin region. Each volunteer was imaged at rest and after performing 5 different simulated surgical procedures using 3D stereophotogrammetry. The simulated surgical movement was determined by measuring the Euclidean distances and the mean absolute x, y and z distances of the landmarks making up the six regions following digitization. A generic mesh was then conformed to each of the aligned six facial 3D images. The same six regions were selected on the aligned conformed simulated meshes and the surgical movement determined by determining the Euclidean distances and the mean absolute x, y and z distances of the mesh points making up the six regions were determined.

Results: In all cases the mean Euclidian distance between the simulated movement and conformed region was less than 0.7 mm. For the x, y and z directions the majority of differences in the mean absolute distances were less than 1.0mm except in the x-direction for the left and right cheek regions, which was above 2.0 mm.

Conclusions: This concludes that the conformation process has an acceptable level of accuracy and is a valid method of measuring facial change between two images i.e. pre- and post-surgery. The conformation accuracy is higher toward the center of the face than the peripheral regions.

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Related in: MedlinePlus

3D image showing 77 facial pre-marked landmarks; left cheek (18 landmarks), right cheek (18 landmark), left upper lip (7 landmarks), philtrum (6 landmarks), right upper lip (7 landmarks) and chin region (21 landmarks).
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pone.0152381.g001: 3D image showing 77 facial pre-marked landmarks; left cheek (18 landmarks), right cheek (18 landmark), left upper lip (7 landmarks), philtrum (6 landmarks), right upper lip (7 landmarks) and chin region (21 landmarks).

Mentions: The individual in this manuscript has given written informed consent (as outlined in PLOS consent form) to publish their images. Following approval by the Institutional Review Board (IRB) of The University of Hong Kong and Hospital Authority Hong Kong West Cluster (UW 14–159); 20 individuals, 10 male and 10 female volunteers, were properly instructed and gave consent to participate in this study by signing the appropriate informed consent paperwork. For each individual 77 facial landmarks were pre-marked in six anatomical regions; left cheek (18 landmarks), right cheek (18 landmark), left upper lip (7 landmarks), philtrum (6 landmarks), right upper lip (7 landmarks) and chin region (21 landmarks), Fig 1. The number and anatomical distribution of the landmarks were standardized by constructing a template; made from hard-cured acrylic with 2mm diameter holes equally spaced 5mm apart. Each template was placed on each specific anatomical area and using a black non-permanent fine eyeliner pen (Dodo Japan Co., Ltd. Tokyo, Japan) the landmarks were placed on the patients skin, the template was removed prior to imaging. Male volunteers with facial hair were excluded in this study.


The Accuracy of Conformation of a Generic Surface Mesh for the Analysis of Facial Soft Tissue Changes.

Cheung MY, Almukhtar A, Keeling A, Hsung TC, Ju X, McDonald J, Ayoub A, Khambay BS - PLoS ONE (2016)

3D image showing 77 facial pre-marked landmarks; left cheek (18 landmarks), right cheek (18 landmark), left upper lip (7 landmarks), philtrum (6 landmarks), right upper lip (7 landmarks) and chin region (21 landmarks).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4836697&req=5

pone.0152381.g001: 3D image showing 77 facial pre-marked landmarks; left cheek (18 landmarks), right cheek (18 landmark), left upper lip (7 landmarks), philtrum (6 landmarks), right upper lip (7 landmarks) and chin region (21 landmarks).
Mentions: The individual in this manuscript has given written informed consent (as outlined in PLOS consent form) to publish their images. Following approval by the Institutional Review Board (IRB) of The University of Hong Kong and Hospital Authority Hong Kong West Cluster (UW 14–159); 20 individuals, 10 male and 10 female volunteers, were properly instructed and gave consent to participate in this study by signing the appropriate informed consent paperwork. For each individual 77 facial landmarks were pre-marked in six anatomical regions; left cheek (18 landmarks), right cheek (18 landmark), left upper lip (7 landmarks), philtrum (6 landmarks), right upper lip (7 landmarks) and chin region (21 landmarks), Fig 1. The number and anatomical distribution of the landmarks were standardized by constructing a template; made from hard-cured acrylic with 2mm diameter holes equally spaced 5mm apart. Each template was placed on each specific anatomical area and using a black non-permanent fine eyeliner pen (Dodo Japan Co., Ltd. Tokyo, Japan) the landmarks were placed on the patients skin, the template was removed prior to imaging. Male volunteers with facial hair were excluded in this study.

Bottom Line: The same six regions were selected on the aligned conformed simulated meshes and the surgical movement determined by determining the Euclidean distances and the mean absolute x, y and z distances of the mesh points making up the six regions were determined.In all cases the mean Euclidian distance between the simulated movement and conformed region was less than 0.7 mm.For the x, y and z directions the majority of differences in the mean absolute distances were less than 1.0mm except in the x-direction for the left and right cheek regions, which was above 2.0 mm.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Dentistry, University of Hong Kong, Hong Kong, China.

ABSTRACT

Purpose: Three dimensional analysis of the face is required for the assessment of complex changes following surgery, pathological conditions and to monitor facial growth. The most suitable method may be "dense surface correspondence".

Materials and methods: This method utilizes a generic facial mesh and "conformation process" to establish anatomical correspondences between two facial images. The aim of this study was to validate the use of conformed meshes to measure simulated maxillary and mandibular surgical movements. The "simulation" was performed by deforming the actual soft tissues of the participant during image acquisition. The study was conducted on 20 volunteers and used 77 facial landmarks pre-marked over six anatomical regions; left cheek, right cheek, left upper lip, philtrum, right upper lip and chin region. Each volunteer was imaged at rest and after performing 5 different simulated surgical procedures using 3D stereophotogrammetry. The simulated surgical movement was determined by measuring the Euclidean distances and the mean absolute x, y and z distances of the landmarks making up the six regions following digitization. A generic mesh was then conformed to each of the aligned six facial 3D images. The same six regions were selected on the aligned conformed simulated meshes and the surgical movement determined by determining the Euclidean distances and the mean absolute x, y and z distances of the mesh points making up the six regions were determined.

Results: In all cases the mean Euclidian distance between the simulated movement and conformed region was less than 0.7 mm. For the x, y and z directions the majority of differences in the mean absolute distances were less than 1.0mm except in the x-direction for the left and right cheek regions, which was above 2.0 mm.

Conclusions: This concludes that the conformation process has an acceptable level of accuracy and is a valid method of measuring facial change between two images i.e. pre- and post-surgery. The conformation accuracy is higher toward the center of the face than the peripheral regions.

Show MeSH
Related in: MedlinePlus