Automatic detection of symmetry plane for computer-aided surgical simulation in craniomaxillofacial surgery.

Symmetry plane calculation is used in fracture reduction or reconstruction in the midface. Estimating a reliable symmetry plane without advanced anatomic knowledge is the most critical challenge. In this work, we developed a new automated method to find the mid-plane in CT images of an intact skull and a skull with a unilateral midface fracture. By use of a 3D point-cloud of a skull, we demonstrate that the proposed algorithm could find a mid-plane that meets clinical criteria. There is no need for advanced anatomical knowledge through the use of this algorithm. The algorithm used principal component analysis to find the initial plane. Then the rotation matrix, derived from an iterative closest point (ICP) registration method, is used to update the normal vector of the plane and find the optimum symmetry plane. A mathematical index, Hausdorff distance (HD), is used to evaluate the similarity of one mid-plane side in comparison to the contralateral side. HD decreased by 66% in the intact skull and 65% in a fractured skull and converged in just six iterations. High convergence speed, low computational load, and high accuracy suggest the use of the algorithm in the planning procedure. This easy-to-use algorithm with its advantages, as mentioned above, could be used as an operator in craniomaxillofacial software.