Magnetic Resonance Imaging of the Temporomandibular Joint in the Mouse

The primary goal in the treatment of temporomandibular joint disorder (TMD) is to ease pain or mandibular dysfunction. Clinically, magnetic resonance imaging (MRI) is routinely used to decide on courses of treatment in TMD patients. In order to develop new medications or new surgical approach, animals experimentation is essential. If the image obtained by MRI is similar to tissue sections of the experimental animals, it considered contributing greatly to the analysis of the structure of the temporomandibular joint (TMJ) and etiology elucidation of TMD.The aim of this study is to investigate the anatomical structure of the TMJ and molecular weight dependency of the synovial membrane permeability were analyzed using MRI in live mice.

Male C57BL6 mice (5-36 weeks old) were used in this study. The mice were anesthetized with pentobarbital, and a venous catheter was inserted into the left femoral vein for the infusion of the relaxation reagents. ¹H MR images were obtained by a 7 T microimaging system (AVANCE III, Bruker Biospin, Ettlingen, Germany) with ParaVison operating software (version 5.1). Three dimensional T₁-weighted MR (3D-T₁wGE) images and three dimensional T₂-weighted MR (3D-T₂wRARE) images were obtained with a 65 μm voxel resolution. Two dimensional T₁wGE images were measured every 45 s before and after bolus intravenous injection of relaxation reagents: Gadolinium (Gd)-DTPA (0.5 kDa) and Gd-albumin (74 kDa). These contrast reagents were used for the dynamic study. The mean image intensity of a small region-of-interest (ROI) in the lower joint cavity, temporal brain, temporal muscle and transverse facial artery and vein were measured. After the experiments, the mice were euthanized by an overdose of pentobarbital. The mice TMJs were dissected, fixed in 10% formalin neutral buffer solution, demineralized in 5% ethylenediaminetetraacetic acid (EDTA), and embedded in paraffin. Paraffin sections were prepared using a slice thickness of 8 μm. The sections were stained by H-E staining.

In the T₁wGE images, the temporal bone and the mandibular condyle were depicted as lower signal intensity regions. The disc was depicted as an intermediate signal intensity region, with a biconcave shape; the posterior and anterior of the disc were thick, and the intermediate of the disc was thin. In the Gd-DTPA-enhanced T₁wGE and T₂wRARE images, the articular disc could be identified as lower signal intensity regions, compared with the upper and lower joint cavities. The structural findings obtained by MRI agreed with those obtained by hematoxylin-eosin staining under light microscopy. After an intravenous injection of the relaxation regent, the image intensities of the transverse facial artery and vein were increased, reaching plateau levels within 3 min. The image intensities of the TMJ was increased by Gd-DTPA within 5-10 min, but no change was shown with Gd-albumin. Contrast enhanced MRI suggested that smaller molecules can permeate the synovial membrane, but larger molecules cannot.

These results suggested that MRI is a useful technique for analyzing the structure of the TMJ and also the permeability of the synovial membrane.

 

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