Magnetic resonance imaging of the temporomandibular joint in dogs and cats. Effect of different coils on image quality.

Objective: In magnetic resonance imaging (MRI) the image quality is considerably affected by the coil used, particularly when small structures are examined. The purpose of this study was to determine which coil provides the best scanning results for imaging of the temporomandibular joint (TMJ) of dogs and cats. Material and methods: MRI investigations were performed using a standard human knee coil and an 8-cm-diameter surface coil with a low-field MRI-system (field strength 0.5 T). TMJs of two dogs and two cats were examined. The scan protocol consisted of T1-weighted spin echo (T1W/SE), 12-weighted turbo spin echo (T2W/TSE), a proton density-weighted sequence (PDW) (slice thickness: 3 mm each), and gradient echo sequences (slice thickness: 1-1.5 mm) in the sagittal plane. Three observers independently compared the features "contrast resolution", "bone structure", "spatial resolution", and "signal-to-noise ratio" (SNR) using a 5-point scale. Investigators were blinded with respect to the coils used. Results: Approximately 50% of the images obtained by the use of the surface coil were rated superior in comparison with the knee coil in terms of the features "contrast resolution", "bone structure", and "spatial resolution". In approximately 50% of the MRI-images no differences in the ratings were seen. With respect to the criterion "signal-to-noise ratio" 90% of the images acquired with the surface coil were rated better. In 5% of the images an identical quality was recorded. The surface coil proved to be superior both in dogs and cats. Conclusions and clinical relevance: Display quality of small structures of the TMJ is dependent on the spatial resolution of the MR images. Therefore, a dedicated coil and a small field of view (FOV) should be used. Results reveal that low-field MRI is able to display subtle anatomic structures of the TMJ in dogs and cats. In principle, the results can be transmitted to other MRI-systems. However, to generate valid scan protocols it is necessary to adapt scan parameters and coil selection specifically.