![]() To overcome the depth limitations of conventional imaging, we recently applied MRI to dynamically visualize the rapid oscillation of the vocal folds in the transverse plane. Recently, dynamic 3D reconstructions of speech production with 15 fps have been presented. ![]() MRI is already an established technique for the visualization of vocal tract dynamics in voice production and singing. Compared to these imaging techniques, MRI is less invasive, it offers different soft tissue contrasts, and it has the potential to visualize the complex motion pattern in arbitrary slice orientations. Cross-sectional measurements of the vocal fold velocities have been performed in the coronal plane using external ultrasonic transducers, or in excised hemilarynges. These imaging techniques share the limitation that the vocal folds can be examined only in a top-down view or need very close contact with the vocal folds. Depth-kymography on the other hand allows to extract depth information from the vocal fold topology via laser triangulation, and optical coherence tomography (OCT) can differentiate individual layers within the vibrating vocal folds. The same holds for high-speed glottography, where the temporal resolution is much higher than with stroboscopy. Thus, laryngeal stroboscopy provides a two-dimensional top-down view of the oscillating vocal folds without any depth information. To better understand the motion and the model, many visualization techniques have been applied.Ĭurrently, laryngeal stroboscopy is the gold standard in dynamic vocal fold imaging-here, an endoscope is inserted transnasally or transorally with a view to the larynx including the vocal folds, and images are acquired in the presence of a stroboscopic illumination which is slightly detuned to the vibration frequency of the vocal folds to capture different phases of the oscillatory motion. In male singers, at a phonation frequency of 150 Hz, a mucosal wave velocity of 4 m/s can be expected. The closure of the vocal folds during phonation is performed by the surface layers in an upward and later side-traveling mucosal wave. This oscillatory system can be described by the biomechanical cover-body model that assumes coupled oscillators of different masses in each vocal fold. The vocal folds consist of the musculus vocalis and the lamina propria, a non-muscular layered structure containing elastin and collagen fibers, which is covered by a thin epithelial layer. ![]() ![]() In addition to static diagnostic imaging, dynamic visualization techniques of vocal fold motion can furthermore provide a better functional understanding of the phonation. To determine the effect of such vocal fold mass lesions on the voice source production, imaging techniques are essential. However, vocal fold pathologies including mass lesions, Reinke’s edema, sulcus vocalis or cancer can significantly alter the mechanical properties of the vocal folds leading to hoarseness or even the inability to phonate. During the latter, the vocal folds can oscillate with fundamental frequencies higher than 1500 Hz. Driven by a subglottal pressure built up by expiratory forces, the vocal folds oscillate and produce sound (phonation) which is modulated by the vocal tract acoustics to allow for a range of expressions in speech and singing. The vocal folds are a key component in the production of human voice. SPIRE is a new MRI method to image rapidly oscillating structures and for the first time provides dynamic images of the vocal folds oscillations in the coronal plane. The simulations emphasize the necessity of SPIRE for two-dimensional motion encoding. Resultsĭynamic images of the vocal folds during phonation at pitches of 150 and 165 Hz were acquired in two volunteers and the periodic motion of the vocal folds at a temporal resolution of about 600 µs was shown. An iterative reconstruction with a total variation (TV) constraint was used and the sequence was also simulated using a motion phantom. Image data were gated using electroglottography (EGG) and motion corrected. In this work, we extend phase encoding to the second image direction by using single-point imaging with rapid encoding (SPIRE) to image the two-dimensional vocal fold oscillation in the coronal view. In our previous work, we achieved high temporal resolution by applying a rapidly switched phase encoding gradient along the direction of motion. The purpose of this study is to introduce a new fast acquisition method and to demonstrate feasibility of encoding rapid two-dimensional motion of human vocal folds with sub-millisecond resolution. The slow spatial encoding of MRI has precluded its application to rapid physiologic motion in the past.
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