Physics-based 3D Head Modeling  
using CT and X-ray Images for Medical Application

Shuji Hashimoto, Masahiko Terajima, Akihiko Nakashima

abstract
   We propose a 3D head modeling method and a prototype of the facial surgery simulation system for surgical prediction of facial deformation using physics-based head model. Our head model has 3D hierarchical structure that consists of three tissues, facial surface and a skull constructed from 3D-CT data, and muscle layer inserted between them. The facial surface and muscles are simulated by physical springs that represent skin and muscles' elasticity. We can realize flexible facial deformation caused by muscles' contraction and jaw action. We call this model "Initial head model". A specific person's head model is reconstructed by the use of anatomical measurement points plotted on the two X-ray images from both of frontal and side views. These measurement points are utilized for the control points in model fitting process, and the other points around them are all moved by their movement vectors which is computed from those of measurement points. The purposes of this research are to analyze the facial soft tissue deformation followed by both of muscles' construction and jaw action for various facial action simulations. In this paper, we focus on the facial surgery simulation, especially Orthodontic surgery. In the experiment, we predicted the facial shape after surgery for patients with mandibular prognathism using our proposed model. By comparing the simulation results with the actual facial images after the surgery, the proposed method can be proved to be practically useful.