Dynamic off-resonance correction for spiral real-time MRI of speech

PURPOSE: To improve the depiction and tracking of vocal tract articulators in spiral real-time MRI (RT-MRI) of speech production by estimating and correcting for dynamic changes in off-resonance. METHODS: The proposed method computes a dynamic field map from the phase of single-TE dynamic images after a coil phase compensation where complex coil sensitivity maps are estimated from the single-TE dynamic scan itself. This method is tested using simulations and in vivo data. The depiction of air-tissue boundaries is evaluated quantitatively using a sharpness metric and visual inspection. RESULTS: Simulations demonstrate that the proposed method provides robust off-resonance correction for spiral readout durations up to 5 ms at 1.5T. In -vivo experiments during human speech production demonstrate that image sharpness is improved in a majority of data sets at air-tissue boundaries including the upper lip, hard palate, soft palate, and tongue boundaries, whereas the lower lip shows little improvement in the edge sharpness after correction. CONCLUSION: Dynamic off-resonance correction is feasible from single-TE spiral RT-MRI data, and provides a practical performance improvement in articulator sharpness when applied to speech production imaging.