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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

(A). Unconformed generic mesh. (B) Conformed mesh with similar shape of the simulated surgical mesh (C), but with the structure and topology.
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pone.0152381.g003: (A). Unconformed generic mesh. (B) Conformed mesh with similar shape of the simulated surgical mesh (C), but with the structure and topology.

Mentions: A modified generic mesh provided by Dimensional Imaging was used for the conformation process. The generic mesh consisted of 3763 vertices and 7327 triangles. For each volunteer the generic mesh and baseline meshes were imported into DiView, twenty four landmarks (Table 1) were placed on the generic mesh and the same twenty four landmarks in same order were digitized on one of the baseline meshs. Using the “shape transfer” function in DiView the three dimensional positions of the twenty four corresponding landmarks on the generic mesh and simulated surgical mesh were used to calculate a warping function that moved all of the landmarks on the generic mesh to the exact position of the corresponding landmark on the simulated surgical mesh. This warping function was then applied to all of the vertices of the generic mesh so that it took on the approximate shape of the simulated surgical mesh. All of the vertices of the warped generic meshs were then projected along the surface normal onto the surface of the simulated surgical mesh, giving the generic mesh the exact shape of the simulated surgical mesh, but with the structured and known topology of the original generic mesh, Fig 3.


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)

(A). Unconformed generic mesh. (B) Conformed mesh with similar shape of the simulated surgical mesh (C), but with the structure and topology.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0152381.g003: (A). Unconformed generic mesh. (B) Conformed mesh with similar shape of the simulated surgical mesh (C), but with the structure and topology.
Mentions: A modified generic mesh provided by Dimensional Imaging was used for the conformation process. The generic mesh consisted of 3763 vertices and 7327 triangles. For each volunteer the generic mesh and baseline meshes were imported into DiView, twenty four landmarks (Table 1) were placed on the generic mesh and the same twenty four landmarks in same order were digitized on one of the baseline meshs. Using the “shape transfer” function in DiView the three dimensional positions of the twenty four corresponding landmarks on the generic mesh and simulated surgical mesh were used to calculate a warping function that moved all of the landmarks on the generic mesh to the exact position of the corresponding landmark on the simulated surgical mesh. This warping function was then applied to all of the vertices of the generic mesh so that it took on the approximate shape of the simulated surgical mesh. All of the vertices of the warped generic meshs were then projected along the surface normal onto the surface of the simulated surgical mesh, giving the generic mesh the exact shape of the simulated surgical mesh, but with the structured and known topology of the original generic mesh, Fig 3.

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