Dynamic MRI of the TMJ under physical load

Abstract

Objectives: The objective of this study was to examine the kinematics of structures of the temporomandibular joint (TMJ) under physiological load while masticating.

Methods: Radial MRI was chosen as a fast imaging method to dynamically capture the motions of the joint's anatomy. The technique included a golden ratio-based increment angle and a sliding window reconstruction. The measurements were performed on 22 subjects with and without deformation/displacement of the intra-articular disc while they were biting on a cooled caramel toffee.

Results: The reconstructed dynamic images provided sufficient information about the size and localization of the disc as well as the change of the intra-articular distance with and without loading.

Conclusions: The feasibility of the golden ratio-based radial MRI technique to dynamically capture the anatomy of the TMJ under physical load was demonstrated in this initial study.

Keywords: magnetic resonance imaging (MRI); temporomandibular joint (TMJ); temporomandibular joint disc.

Figure 1

A sliding window reconstruction with linear (top) vs golden ratio (middle) radial sampling and the k-space-weighted image contrast filter (bottom) is shown. The box depicts the reconstruction window sliding along time axis over the data set. In the two-dimensional images, the k-space of the reconstruction frame is shown. Big and irregular gaps result in strong artefacts. A linearly filled up k-space demands a rather wide reconstruction window that may in turn result in motion artefacts

Figure 2

Typical set-up of a temporomandibular joint measurement. The subject is placed between two multichannel coils that do not interfere with the jaw motion. Cushions stabilize the head to prevent motion artefacts and misaligned slices. All measurements were well tolerated by the subjects

Figure 3

Before and after performing a principle component analysis. A considerable amount of noise could be removed from the image, and the boundaries of the structures become better delineated

Figure 4

Exemplary image series of a healthy joint (right side) during opening of the mouth. The mouth is (upper left) closed at the beginning of the measurement and wide open (bottom right) at the end. The physiological movement of the disc in the intra-articular space is visible (arrow). The series is reconstructed using the k-space-weighted image contrast filter at constant Nyquist sampling

Figure 5

Right temporomandibular joint during an ipsilateral loaded (left) and unloaded (right) closing movement of the jaw. At the end of the series terminal occlusion is reached. While biting on candy, the cartilage in the intra-articular space is more compressed than in the unloaded state

Figure 6

The MR image on the left-hand side shows a static measurement of the temporomandibular joint with imaging parameters comparable with the dynamic measurement. On the right-hand side, the last image of a dynamic series of the same joint in terminal occlusion under loading is shown. The deepest point of the fossa is marked with a line, whereas the dotted and dashed lines indicate the topmost point of the condyle. Note the different distances