Phonovibrogram: vocal fold dynamics integrated within a single image

Background. Stroboscopy is widely used and is quite adequate for the examination of normal voices, but with increasing hoarseness its suitability declines, even when it is supplemented by video recordings and image evaluation. Real-time procedures such as videokymography or high-speed (HS) video imaging are more suitable methods of observing the movements of the vocal folds in such cases. A drawback of any video recording is the later time-consuming offline replay of the films in slow motion and our restricted pattern recognition for motion and other time-dependent processes. Methods. The phonovibrogram (PVG) is an image-processing algorithm that extracts the vocal fold motions of a whole laryngoscopic HS video film and automatically compresses them into a single image. Results. Simple patterns that vary from person to person are revealed by PVG; these can be categorized by means of simple geometric forms, which a human observer can more easily recognize and interpret than dynamic motion patterns. The PVG computation is described in detail and an extensive guide to interpretation is given, illustrated by reference to theoretical and real examples. Conclusion. In clinical conditions, HS laryngoscopic video recording is useful only in association with automatic image processing. The PVG procedure is a promising approach and tests should be performed with a view to further clinical validation.