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

OBJECTIVE/HYPOTHESIS: 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. STUDY DESIGN: An experimental study in which 9 adults underwent high-speed endoscopy combined with a laser projection device. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Laser projection in high-speed glottography for high-precision measurements of laryngeal dimensions and dynamics

The detection of metric dimensions of laryngeal structures yields valuable information for both clinical and research purposes. The use of a laser projection system combined with a high-speed camera system enables the derivation of absolute spatial dimensions of the larynx. Vocal fold length, vibratory amplitudes and velocity can be derived. This was shown on 13 female and 9 male larynges during phonation of a vowel at different pitches. The vocal fold length, the amplitude of oscillation and the velocity of vibration were analyzed in between pitches of 119 to 236 Hz in the male group and 181 to 555 Hz in the female group. The vocal folds length ranged from 8.4 to 14.3 mm in the male group and from 7.7 to 15.6 mm in the female group. Corresponding amplitudes varied from 0.33 to 1.24 mm (male) and from 0.38 to 0.82 mm (female). The maximal velocity of vibration was between 0.48 and 0.85 m/s in males and between 0.47 and 1.3 m/s in females without showing significant correlation between each parameter. The described technique enables the detection of absolute spatial laryngeal dimensions of female and male subjects at different pitches. Dynamic processes such as velocity of vibration can be quantified. The detection of metric data serves to optimize biomechanical model computations and provides valuable information in diagnostics and interpretation of organic and non-organic voice disorders.