Dynamic 3D MRI of vocal fold oscillations: In vivo assessment of vocal fold thickness, contact area, and glottal area waveform across phonation types in comparison with high-speed imaging

Conventional endoscopic imaging of vocal fold (VF) vibration provides only a two-dimensional superior view, missing essential vertical dynamics such as VF thickness and vertical displacement. Simulation studies have assigned these parameters important regulatory functions, underscoring the need for in vivo methods capturing the three-dimensional (3D) VF geometry and vibratory motion. In this in vivo case study, dynamic 3D VF MRI was applied in a professionally trained singer, achieving sub-millimeter spatial and sub-millisecond temporal resolution. Six phonation types were produced according to Estill Voice Training® terminology, each intended to elicit different VF thicknesses and supraglottic configurations. For each type, ten phase-binned 3D datasets of the larynx were reconstructed per oscillatory cycle. Segmentation yielded VF thickness, vertical and horizontal displacement, contact-area dynamics, glottal area waveforms, open quotient (OQ), and supraglottic/subglottic dimensions. These MRI-derived measures showed strong correspondence with those from high-speed imaging and electroglottography acquired from the same subject, indicating that dynamic VF MRI enables reliable in vivo quantification of vibratory and structural parameters. Each phonation type was characterized by distinct VF geometry, supraglottic shaping, and oscillatory behavior. Across types, OQ correlated closely with VF thickness, which systematically covaried with supraglottic adjustments. This suggests supraglottic posturing represents an additional dimension of control.