Visualizing phase relations of the vocal folds by means of high-speed videoendoscopy.

OBJECTIVES To present a method called Fourier image (FI) for analyzing high-speed videoendoscopy recordings. These false-color images visualize functional vocal fold properties and allow the quantification of phase relations. Furthermore, reference data for phase asymmetries in normophonic speakers as assessed with this method are provided. STUDY DESIGN Prospective study. METHODS Phase relations between parts of the vocal folds were assessed using Fourier analysis of the grayscale fluctuations of corresponding pixel within the endoscopic high-speed videos. This phase information was displayed by means of colors and can thus be used to quantify left-right or anterior-posterior phase asymmetries. These phase relations were assessed in 11 normophonic speakers. RESULTS Several instructive examples are given, which demonstrate how the FIs can be interpreted. From the cohort of clinically normophonic speakers, all but one displayed at least some extent of phase asymmetry. CONCLUSIONS The method presented herein can be used to display functional vocal fold properties including the absence of oscillation, glottal insufficiency, and phase relations within one single image. The reference data showed that phase asymmetries seem to be frequent even in normophonic speakers.