Kevin Michael Coughlan
MSc Thesis in the Department
of Computer Science
University of British Columbia, April 1997
Current methods for facial reconstruction are tedious and time-consuming, and require forensic artists with years of practical experience. Furthermore, the complexity of the reconstruction problem greatly increases when time-related factors come into play, such as those that occur in missing children scenarios. This thesis describes a software system for simulating the growth of the craniofacial skeleton. It is a first step towards our goal of a complete software package for three-dimensional craniofacial reconstruction. There is a tremendous amount of data on craniofacial growth in the form of studies that collect frontal and lateral cephalograms, which can be used to generate three-dimensional coordinates of landmarks on the craniofacial skeleton at various ages. We define a simplified model of bone growth that uses these landmarks to drive the growth of the rest of the craniofacial skeleton. The inputs to our growth model include a triangular mesh acquired from the bone to be grown (e.g. skull, mandible), a set of vertices on the mesh identified as landmarks, the coordinates of these landmarks through time, and vertex weights which are a measure of the influence exerted by landmarks on the rest of the vertices. The output is a triangular mesh, ``grown" either forwards or backwards in time to a specified age. An expert in craniofacial growth assigns these vertex weights by using a specialized tool called Krayola. We also provide a tool for automatically generating a first approximation for the vertex weights of a new mesh given the weights previously assigned to a mesh of similar bone type (e.g. skull, mandible). Validation of our growth model is an outstanding issue; we lack three-dimensional data (e.g. from CT scans) for an individual through time, with which we would compare the output of our software. For now, we must be content with the expert opinion of our colleagues in the Department of Dentistry's craniofacial reconstruction group, who are quite pleased with our results so far.