A Modified Protocol to Evaluate Masseter Morphology Based on Automatic Segmentation and Registration

The purpose of the current study was to develop a modified protocol of evaluating the masseter morphology based on graph-cut automatic segmentation. The protocol was applied in the study on pre and postoperative masseter variation in patients receiving mandibular angle reduction. Computed tomography (CT) was used for the image data analysis. The masseter boundary was automatically segmentate on slices. The bony structure of mandible was segmented by the threshold restrain and three-dimensional (3D) reconstructed using the matching cubes algorithm. The pre- and postoperative images of the bony and masseter structures are overlapped in on coordinate system via the ICP registration. The masseter variation was reflected by the measures of the total volume and the 3D surface meshes through comparison of pre- vs. post-operative data. The average volume of the masseter was 32270.5±9354.1 mm3 prior to the surgery, and decreased to 26376.89±7571.4 mm3 and 26650.7±7179.3 mm3 at 6 and 24 months after surgery, respectively. The variation on the cross section at 6 months after the surgery was 6.4±1.5 mm on the angular plane, 2.2±0.9 mm on the occlusion plan and 0.1±0.1 mm on the zygomatic plane. At 24 months after the surgery, the variation was 6.0±1.1 mm on the angular plane, 0.9±0.5mm on the occlusion plane and 0 mm on the zygomatic plane. The 3D color map of the meshes showed that the variation occurred mainly at angular and lower ramous area. The modified protocol was feasible for the evaluation of the masseter morphological variation. 3D comparison between the masseter meshes with representative color map is a convenient and time-saving method to evaluate the morphological variation after mandibular angle reduction.