## 1 Introduction  
The economy of industrialized countries increasingly depends on communication-based professions and the voice is one of the key elements for human communication. It has been shown that the social and economic disadvantage is even higher for people with severe speech disabilities than for those with hearing loss or other disabilities [1]. The primary signal of the voice is generated in the larynx as shown schematically in Figure 1. In a fluid-structure-acoustic interaction, the airflow from the lungs induces an oscillation of the vocal folds that modulates the airflow in return and thus produces an acoustic signal [2]. The oral and nasal cavities represent the vocal tract, where the primary signal is further modulated and speech is thereby generated. Typical vocal fold vibrations display a frequency in the range of 80-300 Hz for normal phonation. In order to capture such rapid movements adequately, high-speed videoendoscopy (HSV) with frame rates in the range of 4-20 kHz is used [3; 4; 5; 6; 7]. In the clinical routine, the most common methods for an evaluation of the vocal fold physiology and dynamical behavior are based on endoscopic, two-dimensional imaging (see Figure 1, left). However, these techniques (stroboscopy, videkymography [8], phonovibrogram [9], HSV, etc.) do not sufficiently reflect the complex vocal fold dynamics as indicated in Figure 1 on the right. [PERSON] et al [10] demonstrated the three-dimensional displacement of the vocal folds in an excised hemilarynx model. It is now mandatory to evaluate the extent of the vertical component during in-vivo recordings and ascertain the possible benefit of 3D imaging for larynx examinations in the clinical routine. In the past, there have been several attempts to capture the 3D movement by means of stereo triangulation. Typically, 3D reconstruction relies on two perspectives and marker points to match both images. For example, in hemilarynx experiments [10; 11; 12], the marker points are sewn into the tissue while the two points of view are provided by the use of a prism. However, non-invasive methods are considered more promising with regard to a clinical application. Following this premise, a recent approach suggested a feature-matching algorithm omitting the marker points completely [13], but the lack of distinct features on vocal folds taints the accuracy of this method. Most 3D reconstruction experiments on the vocal folds use a camera-laser set-up. In this slightly modified version of stereo triangulation, a structured laser light pattern is projected onto the vocal folds and captured by a high-speed camera during phonation. Over the last years, the projection pattern has been continuously developed and refined from its beginnings with individual laser points [14; 15; 16] over laser lines orientated perpendicular to the glottal midline [17; 18; 19] and towards a regular grid pattern [20]. These improvements ultimately enabled a complete three-dimensional reconstruction of the entire visible superior vocal fold surface including the vocal fold edge [21]. 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  
Figure 1: Schematic overview of the three-dimensional vocal fold vibration during phonation: The vertical displacement amplitudes are in the same magnitude as the mainly and commonly analyzed lateral displacement amplitudes [11]. concept set-up from clinical application. The brightness of the laser grid was not sufficient to cover the large variety of different shapes and dimensions in human larynges. An increase of the laser power and consequently the brightness is strictly limited by laser safety regulations and must be carefully considered. Due to the reduced contrast of the laser spots on the vocal folds, the subsequent image processing was severely impaired, leading to an exclusion of many recordings.