One-second MRI of a three-dimensional vocal tract to measure dynamic articulator modifications

To enable three-dimensional (3D) vocal tract imaging of dynamic singing or speech tasks at voxel sizes of 1.6 × 1.6 × 1.3 mm³ at 1.3 s per image.

A Stack-of-Stars method was implemented and enhanced to allow for fast and efficient k-space sampling of the box-shaped vocal tract using a 3 Tesla MRI system. Images were reconstructed using an off-line image reconstruction using compressed sensing theory, leading to the abovementioned spatial and temporal resolutions. To validate spatial resolution, a phantom with holes of defined sizes was measured. The applicability of the imaging method was validated in an eight-subject study of amateur singers that were required to sustain phonation at a constant pitch, past their comfortable expiratory level. A segmentation of the vocal tract over all phonation time steps was done for one subject. Anatomical distances (larynx position and pharynx width) were calculated and compared for all subjects.

Analysis of the phantom study revealed that the imaging method could provide at least 1.6 mm isotropic resolution. Visual inspection of the segmented vocal tract during phonation showed modifications of the lips, tongue, and larynx position in all three dimensions. The mean larynx position per subject amounted to 52-85 mm, deviating up to 5% over phonation time. Parameter pharynx width was 32-181 mm² on average per subject, deviating up to 16% over phonation time. Visual inspection of the parameter course revealed no common compensation strategy for long sustained phonation.

The results of both phantom and in vivo measurements show the applicability of the fast 3D imaging method for voice research and indicate that modifications in all three dimensions can be observed and quantified.

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:94-101.