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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) Superimposed conformed mesh baseline (grey) and baseline textured image showing the 21 landmarks of the chin region and the region in red selected on the baseline conformed mesh. (B) The conformed mesh showing the chin region in red selected on the baseline conformed mesh used to assess simulated mandibular surgery. This allows direct comparison with the 21 chin region landmarks.
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pone.0152381.g004: (A) Superimposed conformed mesh baseline (grey) and baseline textured image showing the 21 landmarks of the chin region and the region in red selected on the baseline conformed mesh. (B) The conformed mesh showing the chin region in red selected on the baseline conformed mesh used to assess simulated mandibular surgery. This allows direct comparison with the 21 chin region landmarks.

Mentions: For each patient the original baseline 3D textured image and their baseline conformed mesh were imported into MeshLab software (STI-CNR, Rome, Italy; http://meshlab.sourceforge.net/). Using the “select face” function in MeshLab the triangles on the conformed mesh that represented the similar region of interest on the textured image was selected, Fig 4. This was repeated for each of the six regions of interest on the conformed baseline mesh. Each conformed baseline mesh image and selected region was re-saved in Polygon file format (.PLY) with “flags” attached to the selected triangles within the file structure. The remaining simulated surgical movement.OBJ files were imported into MeshLab and re-saved as.PLY to produce a common file format. Using MATLAB the vertices associated with the “flagged” triangles were identified. Since all the images were conformed using the same generic mesh these flagged triangles and vertices could be identified on all the meshes and would represent the same region between them all, hence providing direct correspondence. The mean Euclidian distances and the mean absolute distances in the x, y and z directions between corresponding vertices making up the region were calculated.


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) Superimposed conformed mesh baseline (grey) and baseline textured image showing the 21 landmarks of the chin region and the region in red selected on the baseline conformed mesh. (B) The conformed mesh showing the chin region in red selected on the baseline conformed mesh used to assess simulated mandibular surgery. This allows direct comparison with the 21 chin region landmarks.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0152381.g004: (A) Superimposed conformed mesh baseline (grey) and baseline textured image showing the 21 landmarks of the chin region and the region in red selected on the baseline conformed mesh. (B) The conformed mesh showing the chin region in red selected on the baseline conformed mesh used to assess simulated mandibular surgery. This allows direct comparison with the 21 chin region landmarks.
Mentions: For each patient the original baseline 3D textured image and their baseline conformed mesh were imported into MeshLab software (STI-CNR, Rome, Italy; http://meshlab.sourceforge.net/). Using the “select face” function in MeshLab the triangles on the conformed mesh that represented the similar region of interest on the textured image was selected, Fig 4. This was repeated for each of the six regions of interest on the conformed baseline mesh. Each conformed baseline mesh image and selected region was re-saved in Polygon file format (.PLY) with “flags” attached to the selected triangles within the file structure. The remaining simulated surgical movement.OBJ files were imported into MeshLab and re-saved as.PLY to produce a common file format. Using MATLAB the vertices associated with the “flagged” triangles were identified. Since all the images were conformed using the same generic mesh these flagged triangles and vertices could be identified on all the meshes and would represent the same region between them all, hence providing direct correspondence. The mean Euclidian distances and the mean absolute distances in the x, y and z directions between corresponding vertices making up the region were calculated.

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