Objective vocal fold vibration assessment from videokymographic images

Vocal folds oscillation crucially influences all the basic qualities of voice, such as pitch and loudness, as well as the spectrum. Stroboscopy provides the standard view of the larynx. However, a two-dimensional high-speed imaging system currently cannot provide enough image resolution to evaluate irregular vocal fold vibrations, due to the limitation of transmission speed and storage volume. Videokymography is a new diagnostic tool developed to overcome specific limitations of stroboscopy in severely dysphonic patients with an aperiodic signal. It registers the movements of the vocal folds with a high time resolution on a line perpendicular to the glottis. The technique, being independent from the periodicity and intensity of the vocal signal, allows an objective evaluation of vocal folds function. However, due to its novelty, no established clinical evaluation protocol, or validity and reliability data are available for videokymography. Moreover, few results concerning objective parameter estimation from videokymographic images are available. The main focus of this paper is on measuring and tracking quantitative parameters for objective vocal fold functional assessment, from videokymographic (VKG) examinations of subjects with normal and pathological laryngeal function, based on active contour search implemented with a properly adjusted robust snake algorithm. The method is designed to deliver to the clinician the essential objective information of VKG in an effective way, as an aid to its subjective and intuitive skilfulness. A set of VKG images has been analysed, coming both from healthy and dysphonic subjects, recorded at the Otolaryngology Department, University of Milan, Italy, showing the robustness and reliability of the proposed technique.