A bridging method between 2D and 3D cephalometry using computed tomography synthesized cephalograms

Traditional cephalograms are X-ray films, which provide either frontal or lateral overlapped perspective medical imaging. Although computed tomography imaging provides more information in 3-dimensional anatomy, the landmarks for cephalometry are located in space which does not carry normal standards in 3-D cephalometry. The CT natural imaging method is different from X-ray in that they respectively use orthogonal and perspective projections. Thus, we cannot apply the statistical normal values gathered from traditional 2D cephometry to 3D cephalometry. This study makes use of calibrated synthesized cephalograms from computed tomography to construct a cephalometry bridge between 2-D and 3-D. In this thesis, we first review the imaging model of a specific X-ray machine (Asahi OrthoStage AUTO IIIN) by a camera calibration method. We then construct a reference system for a virtual head, and synthesize calibrated X-ray cephalograms using the volume rendering algorithm. System accuracy for the synthesis X-ray cephalograms is verified through an interactive corresponding landmark system between 2-D and 3-D. An experimental clinician was invited to manually place 17 landmarks on the X-rays and their corresponding, shuffled in random order. The systematic error, average error, and standard deviation of landmark positions are 0.15 mm, 0.97 mm, and 0.45 mm, respectively. The interactive system bridges the transformation from orthogonal 3-D to perspective 2-D cephalometry.