Are High-Speed Digital Videoendoscopy Systems The Future Of Laryngology?

Abstract

Since Hirano's original description of the layered microanatomy of the human vocal fold in the 1970s, increasingly sophisticated diagnostic and surgical techniques have evolved to address this delicate and complex structure more appropriately. 1 Innovative diagnostic modalities have grown out of an improved understanding of the critical importance of vocal fold oscillation to voice production. Videostroboscopy has evolved as one of the most practical and useful techniques for the clinical evaluation of vocal fold vibration and fulfils several important requirements of a complete voice examination. It provides useful information concerning the nature of vibration, an immediate image to detect the presence or absence of vocal pathology, and a permanent video record of the examination. Strobolaryngoscopy takes advantage of Talbot's law (persistence of vision) by producing intermittent light flashes in relation to the speed of the vocal fold vibration. 2 The frequency of the study subject's sustained voice is picked up by a microphone and triggers the stroboscopic light source. With the provision that the vocal vibrations are periodic, a frequency of light flashes equal to the vocal frequency will produce a clear still image of the same portion to the vibratory cycle. When the frequency of the flashes is slightly less than the vocal fold vibration, causing a delay in the portion of each vibratory cycle illuminated, the illusion of slow motion is obtained. While videostroboscopy greatly expands the diagnostic sensitivity of laryngoscopy, its interpretation is dependent upon the skill and experience of the clinician and, more specifically, the diagnostic interpreter. An admitted limitation of the stroboscopic image is that vocal fold vibration must be relatively periodic to visualize a slow motion representation of the phonatory cycle. 2 However, this limitation can be greatly reduced by combining electroglottography (uses the glottal waveform) with videostroboscopy. Efforts to extend the sensitivity of laryngoscopy to incorporate variations of wave characteristics across the glottis as well as aperiodic patterns of vibration have yielded new techniques. Videokymography (VKG) was developed in 1994 in Groningen (NL) as a lowcost alternative high-speed imaging system especially suited to examination of vocal fold vibration. 3 The system uses a special CCD video camera which can work in two different