Deformable modeling of facial tissue for craniofacial surgery simulation.

While deformable object modeling has been studied by computer graphics specialists for more than two decades, only a few applications in the field of surgical simulation have been developed which provide both real-time and physically realistic modeling of complex, nonlinear tissue deformations. Particularly in craniofacial surgery, the prediction of soft-tissue changes--which result from alterations in the underlying bone structure--is critical to the surgical outcome. The prediction these tissue changes and, therefore, the prognosis of the postoperative appearance of the patient, is still based on empirical studies of the relationship between bone and tissue movements: There exists no physical model which takes into account the individual patient anatomy to simulate the resulting tissue changes during craniofacial surgery. In this article we present two different deformable tissue models which are intergrated in an interactive surgical simulation test bed. Both techniques allow precise preoperative simulation of the resulting soft tissue changes during craniofacial surgery and visualization of the patient's postoperative appearance. The different deformable models are described in detail and both are applied to the same craniofacial case study. The simulation results are shown and compared with regard to the speed and accuracy of the prediction of the patient's postoperative appearance.