Extraction of 3D trajectories of mandibular condyles from 2D real-time MRI

TL;DR

This study demonstrates that 2D real-time MRI can be used to extract 3D mandibular condyle trajectories with sufficient accuracy for clinical assessment, despite some limitations in precision due to head motion and segmentation challenges.

Contribution

It introduces a novel method for deriving 3D condylar trajectories from 2D MRI slices, combining segmentation and coordinate projection techniques.

Findings

Segmentation quality was good for axial slices but variable for sagittal slices.

Reproducibility of movement was acceptable, with some displacement due to head motion.

Average difference in condyle position was 1.7 mm in closed jaw position.

Abstract

Computing the trajectories of mandibular condyles directly from MRI could provide a comprehensive examination, allowing for the extraction of both anatomical and kinematic details. This study aimed to investigate the feasibility of extracting 3D condylar trajectories from 2D real-time MRI and to assess their precision.Twenty healthy subjects underwent real-time MRI while opening and closing their jaws. One axial and two sagittal slices were segmented using a U-Net-based algorithm. The centers of mass of the resulting masks were projected onto the coordinate system based on anatomical markers and temporally adjusted using a common projection. The quality of the computed trajectories was evaluated using metrics designed to estimate movement reproducibility, head motion, and slice placement symmetry.The segmentation of the axial slices demonstrated good-to-excellent quality; however, the segmentation of the sagittal slices required some fine-tuning. The movement reproducibility was acceptable for most cases; nevertheless, head motion displaced the trajectories by 1 mm on average. The difference in the superior-inferior coordinate of the condyles in the closed jaw position was 1.7 mm on average.Despite limitations in precision, real-time MRI enables the extraction of condylar trajectories with sufficient accuracy for evaluating clinically relevant parameters such as condyle displacement, trajectories aspect, and symmetry.