A New Coordinate System for Magnetic Resonance Imaging of the Vestibular System.

To develop and evaluate a new coordinate system for MRI of the vestibular system. In this study, 53 internal auditory canal MRI and 78 temporal bone CT datasets were analyzed. Mimics Medical software version 21.0 was used to visualize and three-dimensionally reconstruct the image data. We established a new coordinate system, named W-X, based on the center of the bilateral eyeballs and vertex of the bilateral superior semicircular canals. Using the W-X coordinate system and Reid's coordinate system, we measured the orientations of the planes of the anterior semicircular canal (ASCC), the lateral semicircular canal (LSCC), and the posterior semicircular canal (PSCC). No significant differences between the angles measured using CT and MRI were found for any of the semicircular canal planes ( > 0.05). No statistical differences were found between the angles measured using Reid's coordinate system (CT) and the W-X coordinate system (MRI). The mean values of ∠ASCC & LSCC, ∠ASCC & PSCC, and ∠LSCC & PSCC were 84.67 ± 5.76, 94.21 ± 3.81, and 91.79 ± 5.22 degrees, respectively. The angle between the LSCC plane and the horizontal imaging plane was 15.64 ± 3.92 degrees, and the angle between the PSCC plane and the sagittal imaging plane was 48.79 ± 4.46 degrees. A new W-X coordinate system was developed for MRI studies of the vestibular system and can be used to measure the orientations of the semicircular canals.