CRÁNEO


  • Soft Tisue Reconstruction
  • Superposition Skull-Photo
Funding Entity: 

Project funded in 2008 through the program PROFIT (Tractor project) by the Spanish Ministry of Industry, Tourism and Commerce.


Start Date: 
Tuesday, 1 January 2008 to Friday, 31 December 2010
Stage: 
Closed
Design and introduction of software solutions in legal and forensic medicine

Development of a software application to reconstruct individual faces starting from their skull in legal and forensic medicine.

Human identification from a skull is a critical process in legal and forensic medicine, especially when no other means are available. Traditional clay-based methods attempt to generate the human face, in order to identify the corresponding person. However, these reconstructions lack of objectivity and consistence, since they depend on the practitioner. Moreover, the results of the reconstruction cannot be easily distributed and consulted from everywhere.

The objective of this project is to develop a 3D craniofacial reconstruction automatic system. Moreover, a web application has been developed, so results can be consulted and modified by authenticated users via web. The whole system consists of a main application able to generate a 3D mesh simulating the skin of a person from the 3D image corresponding to his/her skull. Facial features are not included in the generated mesh, as they cannot be confidently deduced only from skull. For this purpose, a completely objective method is used. On the other hand, both input data and reconstructions generated by the main application are contained in a database which can be accessed from the Internet.

Another objective of the project CRÁNEO, is the development of a software that automates the process of skull-photo superimposition used by forensic experts in identifying character. This software will automatically superimpose the 3D geometry of the scanned skull with any 2D photograph regardless of the angle it was taken allowing to make a large number of overlays in a rapid and automatic way.

Finaly, another task has been to create a web application that will serve as medical documentation center networking. The application will be used by any registered expert system can access and view any of the subjects and their associated data stored in a remote database through a web browser, from anywhere, just need an internet connection.

Results:

Soft tissue generation process

  • 3D Facial Reconstruction. The main application scheme comprises the following elements (see Figure):

craneo-schema.png

Main application scheme

  • Input Data:Set of data used by the application to generate the soft tissue mesh. Three different input data are required:
    • Skull image: a 3D image of the skull needed to obtain its facial reconstruction.
    • 66 landmark points placed on the skull surface: in those reference points, soft tissue depth is known.
    • Age, gender and BMI range of the person the skull belongs to. Age and gender can be deduced from skull morphology, so they will always be known by the user. However, BMI range will be an unknown parameter, so it will be estimated.
  • Landmark insertion module (LIM):in charge of placing the 66 reference points on the skull surface, and assigning them a tissue depth value, according to age, gender and BMI parameters. The reference points used for this purpose are two sets of points traditionally used in forensic medicine:

craneo-landmarks.png

Lanndmark definition used for craniofacial reconstruction in the project: set of 52 points to generate facial reconstruction in facial zone (black) and set of 14 points to generate craniofacial reconstruction in neurocranium (red)

  • Soft tissue generation module:the Skin Mesh Generation Module (SMGM) block represents the main functional module in the application. Based on the output data generated in LIM, it generates a set of intermediate points on the skull surface, whose depth values can be interpolated from thickness values in reference points (see next Figure). The whole set of points (landmarks and intermediate points) are used to build the final 3D mesh representing the soft tissue (skin) corresponding to the given skull.

craneo-reconstruction.jpg

Soft tissue generation process

  • Skull-Photo Superimposition. The main application scheme comprises the following elements (see Figure):

sobreimposicion.png

Skull-Photo Superimposition scheme

  • Input Data:Set of data used by the application to generate the soft tissue mesh. Three different input data are required:
    • Skull image: a 3D image of the skull needed to obtain its facial reconstruction.
    • 5 landmark points placed on the skull surface.
    • 5 cefalometric points placed on 2D photo.
  • Facial Features Detection Module: this module is capable of detecting face, eyes and nose automatically on the photography. These positions will be useful to calculate cefalometric points correctly.

craneo-cara-1.png

Face, Eyes and Nose areas detected on photo.

  • 3D Points Insertion Module:this module places the set of 5 reference points on the 3D skull. For this module, the implementation already developed in 3D Facial Reconstruction has been used (see Landmark insertion module).  
  • 2D Points Insertion Module:The 2D Points Insertion Module places the set of 5 reference points on the photograph

craneo-cara-2.png

Example of photo with final points calculated.

  • Homography Calculation Module: After estimating the position of the points on the skull and on the photograph, it is necessary to calculate the correlation between them. The correlation between the two set of points is performed using a homography. Homography [Hartley and Zisseman (2000), Hartley and Zisseman (2003)] is a special projective transformation which relates the coordinate system  x =[x1, x2] con with x’  =[x’1, x’2] (see figure).

craneo-homoghafia.png

Example of homography between 2 sets of points

  • Matching Module: The Matching Module calculates the degree of correspondence between skull and photograph points after they have been correlated by the Homograph.
  • Medical Documentation Centre Online

On the other hand, a Web environment of the 3D reconstruction application has been implemented to allow the remote visualization of both the input data and generated reconstructions obtained by the main application.

The interaction between remote (web) users and the main application is illustrated in the following figure. Through this scheme a user can visualize and modify via Internet any information contained in the application database (skull information and generated reconstructions). 

craneo-web_eng.png

Interaction between main application and web users

 

 

Video demo of reconstruction application