Limits...
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.

Show MeSH

Related in: MedlinePlus

21 chin region landmarks used to measure surgical simulation of left mandibular displacement (B) from the baseline rest image (A).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4836697&req=5

pone.0152381.g002: 21 chin region landmarks used to measure surgical simulation of left mandibular displacement (B) from the baseline rest image (A).

Mentions: Following alignment the Euclidian distances and the absolute distances in the x, y and z directions between corresponding landmarks on the baseline mesh and each of the simulated surgical meshes were used to assess the actual soft tissue change of each region. This was carried out by digitizing the landmarks in the region of interest using DiView. For example, to assess simulated mandibular advancement (mandible to left), following alignment of the baseline mesh with the mandibular to left mesh, the chin region landmarks were digitized on both meshes and exported, Fig 2. Using MATLAB (MathWorks, Cambridge, UK) the Euclidian distances between each of the 21 corresponding points together with the mean and standard deviation were calculated. The same procedure was carried out for the remaining simulated surgical movement. The chin region was used to assess the three different mandibular simulated surgical movement, whilst the left, right and philtrum regions of the upper lip and cheek regions were used to assess the maxillary simulated surgical movements.


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)

21 chin region landmarks used to measure surgical simulation of left mandibular displacement (B) from the baseline rest image (A).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0152381.g002: 21 chin region landmarks used to measure surgical simulation of left mandibular displacement (B) from the baseline rest image (A).
Mentions: Following alignment the Euclidian distances and the absolute distances in the x, y and z directions between corresponding landmarks on the baseline mesh and each of the simulated surgical meshes were used to assess the actual soft tissue change of each region. This was carried out by digitizing the landmarks in the region of interest using DiView. For example, to assess simulated mandibular advancement (mandible to left), following alignment of the baseline mesh with the mandibular to left mesh, the chin region landmarks were digitized on both meshes and exported, Fig 2. Using MATLAB (MathWorks, Cambridge, UK) the Euclidian distances between each of the 21 corresponding points together with the mean and standard deviation were calculated. The same procedure was carried out for the remaining simulated surgical movement. The chin region was used to assess the three different mandibular simulated surgical movement, whilst the left, right and philtrum regions of the upper lip and cheek regions were used to assess the maxillary simulated surgical movements.

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