Real-time MR Imaging of Temporomandibular Joint Functions at High Resolution

Purpose: To introduce a novel method for real-time magnetic resonance imaging (MRI) that yields high-quality images for assessment of dynamic temporomandibular joint (TMJ) functions. Methods: The approach combines three major principles: (i) a fast low-angle shot (FLASH) gradient-echo MRI technique, which allows for rapid and continuous image acquisitions without sensitivity to off-resonance artifacts, (ii) an interleaved radial encoding scheme, which in contrast to Cartesian data sampling offers motion robustness and moderate tolerance to data undersampling, and (iii) a “sliding-window” reconstruction strategy, which increases the image reconstruction rate by a factor of 3 to 5. The proposed technique was implemented on a clinical 3 T MRI system (Siemens AG, Erlangen, Germany) without any hardware modifications. Studies with 30 subjects on both sides were performed and evaluated with respect to the image quality and stability. Results: During voluntary mouth opening and closing without using biting devices, real-time MRI movies based on radial T1/T2-weighted FLASH images (TR/TE = 4.3/2.2 ms, flip angle 20º) were obtained at 0.75 mm in-plane resolution (5 mm thickness) along oblique sagittal orientation and with 3 frames per second temporal resolution. Through online monitoring the condyle movement (arrow heads in Fig 1) and corresponding articular disc displacement (arrows in Fig 1) were visualized with good image contrast. Statistics based on data evaluation concerning motion artifacts and visibility of anatomical structures and physiological changes showed excellent rating score over all studies (>88.4% positive) and high agreement among 2 TMJ and 2 MRI experts (kappa = 0.72). Conclusion: The proposed real-time MRI technology outperforms previous trials and demonstrates considerable potential for assessment of dynamic TMJ functions under both normal and pathological conditions in routine clinical examinations.