Highly Accurate CAD Tools for Cranial Implants

Prefabricated patient-specific cranial implants are especially useful for large cranial defects. We present CAD tools for large cranial implants that include validation of fit prior to rapid prototype fabrication. Our CAD process first determines whether the prototype implant surface intersects adjacent soft-tissue structures via collision detection. If so, we measure the volume of both the intersected dura and unoccupied area under the implant. These data are used to determine whether the prototype implant requires modification. If modification is necessary, we deform the prototype implant surface via a thin plate spline warp. Second, we interactively create and verify the implant taper surface that connects the external and internal implant surfaces. The taper surface seats the implant onto the patient’s cranial defect site. The taper and patient’s skull surfaces may contact but must not intersect one another. Results from tests on five patient data sets show our CAD and validation methods result in implant designs which are an improvement over, and not feasible by, current manual implant preparation methods.