3D Reconstruction of Human Laryngeal Dynamics Based on Endoscopic High-Speed Recordings

Abstract

Standard laryngoscopic imaging techniques provide only limited two-dimensional insights into the vocal fold vibrations not taking the vertical component into account. However, previous experiments have shown a significant vertical component in the vibration of the vocal folds. We present a 3D reconstruction of the entire superior vocal fold surface from 2D high-speed videoendoscopy via stereo triangulation. In a typical camera-laser set-up the structured laser light pattern is projected on the vocal folds and captured at 4000 fps. The measuring device is suitable for in vivo application since the external dimensions of the miniaturized set-up barely exceed the size of a standard rigid laryngoscope. We provide a conservative estimate on the resulting resolution based on the hardware components and point out the possibilities and limitations of the miniaturized camera-laser set-up. In addition to the 3D vocal fold surface, we extended previous approaches with a G2-continuous model of the vocal fold edge. The clinical applicability was successfully established by the reconstruction of visual data acquired from 2D in vivo high-speed recordings of a female and a male subject. We present extracted dynamic parameters like maximum amplitude and velocity in the vertical direction. The additional vertical component reveals deeper insights into the vibratory dynamics of the vocal folds by means of a non-invasive method. The successful miniaturization allows for in vivo application giving access to the most realistic model available and hence enables a comprehensive understanding of the human phonation process.

Experimental study on level difference between left and right vocal folds

“…There have been however not much reports on the physiological measurement of the level difference, because conventional tools such as stroboscopy and high-speed video endoscopy are limited to providing information regarding glottal movement in the transverse plane [17]. Recently, various attempts have been made to obtain three-dimensional information of the vocal fold dynamics, e.g., laser systems [18], stereo endoscopy [19], and others. Such advanced measurements may provide more precise information about the left-right vertical asymmetry and enable us to study the relation between the level difference and the difficulty of phonation.…”

Endoscopic Laser-Based 3D Imaging for Functional Voice Diagnostics

“…The projection of a laser beam array on the superior surface of the vocal folds during phonation enables their 3D reconstruction when captured with a high-speed camera. A detailed explanation of the underlying principle and measurements concerning the accuracy can be found in [22]. In order to realize this concept, the miniaturized set-up as shown in Figure 2 consists of two basic elements, namely the imaging unit and the projection unit.…”

“…The vocal fold edge is then modelled by a G2-continuous Bezier curve towards the most medial point on the vocal fold, reflecting the natural tissue curvature. An in-depth description of the interpolation and edge modelling can be found in [22]. Various 3D parameters like mean and maximum amplitude and velocity in different phases of the oscillation cycle can be derived from the resulting 3D vocal fold surface model.…”

“…The specificity, however, is significantly increased by 38.3%. Statistical analysis using IBM SPSS Statistics v21 (i.e., pairwise comparison of video frames over all series, applying Wilcoxon Rank Test -data was not normally distributed) showed a statistically highly significant improvement (p = 0.000) between the methods of Luegmair [20] and Semmler [22] for both measures. As before, the standard deviation of the specificity is reduced from 37.1% to 25.4%, which indicates a decreased dependence on the quality of the high-speed footage.…”

“…Lately, this concept was transferred to in vivo application by means of miniaturization of the laser projection unit [22]. However, the following shortcomings still separate this experimental proof of concept set-up from clinical application.…”