High-precision measurement of the vocal fold length and vibratory amplitudes.

Abstract

Standard laryngoscopy suffers from a lack of information about the actual size of the observed objects (i.e., vocal fold length and oscillating amplitudes). However, there is much interest in absolute measures for both clinical and research purposes. Therefore, a laser projection device has been developed that enables the precise determination of absolute units in endoscopic investigation during respiration and phonation. An experimental study in which 9 adults underwent high-speed endoscopy combined with a laser projection device. The projection system consists of two parallel laser beams with a distance of 3.8 mm. It is mounted on the tip of a rigid endoscope, which is attached to a digital high-speed camera During development and design, examination situations were taken into account. Two laser spots are projected onto the vocal folds and enable the definition of a metric scale within the endoscopic image. Knowledge-based image processing algorithms were used for evaluation. First measurements of the vocal fold length during phonation were performed in a group of nine healthy male students. The determination of glottal length during phonation agrees with former results. Quantifying vocal fold velocities in absolute units makes it possible to estimate the initial collision forces. The presented laser projection system allows the determination of absolute measures in the larynx. Because of the simple functional principle, the system is open for use without digital high-speed recording as well. Absolute units may also be helpful in voice diagnosis and in monitoring during voice therapy.