Finite Element Analysis of the Facial Skin

Prepared by:

Dr. A. Zeiny

April 2000

1. Introduction:

Since the human face plays a key role in interpersonal relationships, prediction of post-surgical morphology and appearance of human faces for patients with facial deformities is a critical issue in facial surgery. Even very subtle malformations of facial proportions can strongly affect the appearance of a face and determine on aesthetic aspects such as individual beauty. In addition, many procedures in maxillofacial surgery lead to a change in the facial morphology of the patient, e.g. cutting of the jawbones and bringing them into a desired position. Maxillofacial surgery also consists of the resection of malformed parts of the face or tumors and reconstruction of missing or malformed structures. Furthermore, the treatment of patients with facial fractures influences facial shape and surface. Therefore, surgeons often face the problem of predicting a fair facial surface before the actual surgery is carried out. Figure l illustrates a typical malformation of a young girl's face and its correction by surgery. Typically, the maxillofacial surgeon with the help of a medical artist draws the patients predicted profile to give at least a 2D appearance of the future face. It is clear that both surgeons and their patients have a strong demand for a method, which enables them to compute highly realistic 3D pictures of the post surgical shape. Any computation should be based on data obtained from the patient, e.g. CT scans. More specifically, with the development of advanced range scanners the idea was born to combine both volume and surface data to build a physically based facial model. Obviously, the model has to capture the most important anatomical and mechanical parameters of' the face. Furthermore, it should allow interactive manipulations and the prediction of resulting facial shape.

2. Objective Of Research:

The purpose of this research project is to use modern numerical analysis techniques to analyze the human face. This project will produce a software package that is capable of inputting the shape of a face, and then manipulating that face to simulate the effects of reconstructive surgery on the shape of the face. The interface of the proposed software is shown in Figure 2. This software could be used in the medical industry by doctors and plastic surgeons to aid them in preparation for maxillofacial surgery.

Figure 1: Typical malformation of a young girl's face

Figure 2: Proposed Software Package

3. Proposed Approach:

The proposed task will be to implement using the finite element numerical technique coupled with advanced computer graphics packages. The finite element will be used to model the mechanical and biological properties of the facial skin. A pre-processor interfacing unit will be developed to convert medical data into finite element data. The post-processing unit takes the deformed wire frame resulting from the finite element analysis and renders the predicted new shape of the human face.

4. References:

· Pieper S, "More than Skin Deep: Physical Modeling of Facial Tissue", M.S. Thesis, MIT Media Lab, Cambridge MA, 1989

· Komatsu, K., "Human skin model capable of natural shape variation", The Visual Computer, Volume 3, No. 5, pp. 265-271, 1988

· W. Larrabee, "A finite element model of skin deformation I: Biomechanics of skin and soft tissue: A review", Laryngoscope, Volume 96, pp. 399-419, 1986

· Kirby, S.D., Wang, B., To, C.W.S., and Lampe, H.B., "Nonlinear three dimensional finite element model of skin biomechanics", Journal Of Otolaryngology, Volume 27, No. 3, pp.153-160, June1998

· Manios, A; Katsantonis, J; Tosca, A; Skulakis, C; and others. “The finite element method as a research and teaching tool in the analysis of local skin flaps”, Dermatologic Surgery, Volume 22, No. 12, pp.1029-1033, December 1996