Dynamic display of the temporomandibular joint meniscus by using "fast-scan" MR imaging

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Abstract
In order to display temporomandibular joint (TMJ) images as a dynamic or motion study, a protocol was developed to obtain MR images of the TMJ in multiple phases of opening by using the "fast-scanning" capabilities of the GE Signa MR scanner. To facilitate this procedure a prototype device was also developed to passively open the patient's mouth from resting (closed) to fully open in user-defined increments (minimum 1 mm). MR imaging (surface coil) was carried out at each successive station using the GRASS, pulse-sequence data base of the GE Signa system operating at 1.5 T. Image-acquisition parameters were optimized in studies of cadavers and volunteers to obtain the clearest delineation of the TMJ meniscus and to determine any potential tradeoffs between total imaging time per slice (image quality), patient tolerance, and other practical considerations. For viewing, the images were sequentially placed in the video memory of the operating console and displayed in a back-and-forth-closed cine loop or "movie" mode at variable (operator-selectable) speeds. The dynamic sequences in four individuals were compared with static open- and closed-mouth views obtained with routine pulse sequences. Any single image from the dynamic display lacked the high resolution of the routine static images because of technical limitations of the pulse-sequence data base. However, in the movie mode the pertinent joint structures (such as meniscus and condyle) were clearly delineated, as were several of the important muscles of mastication. The anterior motion (translation) of the meniscus during jaw opening is particularly evident and suggests great potential for functional evaluation. These results show the feasibility of dynamic TMJ imaging with MR. The added information of the cine display potentially complements the routine static images and may prove extremely valuable in the assessment of TMJ dysfunction.