TVF2020-BSc3 : Horizontal Calibration for a Laser-Projection Transnasal Fiberoptic HSV system
Channel: Hamzeh G.
Date: 14/05/2020

This is the presentation for The Voice Foundation 2020

Title: 
"Horizontal Calibration for a Laser-Projection Transnasal Fiberoptic High-Speed Videoendoscopy system".

Authors:
Hamzeh Ghasemzadeh, MSc, PhD Candidate in Department of Communicative Sciences and Disorders, Michigan State University; PhD Candidate in Department of Computational Mathematics Science and Engineering, Michigan State University, email: ghasemza@msu.edu 

Dimitar D. Deliyski, PhD, Professor and Chair, Department of Communicative Sciences and Disorders, Michigan State University.

Abstract:
Objective: An automated method for horizontal calibration of a laser-projection transnasal fiberoptic high-speed videoendoscopy (HSV) system was developed. The optical principle of the developed laser-calibrated endoscope is to project a grid of 7×7 green laser points across the field of view (FOV) at an angle relative to the imaging axis. Considering that each laser point had a slightly different angle from the imaging axis, the projected laser points were not parallel. This implies that, the vertical distance would be a confounding factor for horizontal calibration and subsequent horizontal measurements. The objectives of this research were to develop the methodology for horizontal calibrated measurement and to quantify the measurement error of the developed method. 
Method: A custom-built transnasal fiberoptic endoscope was used to project a grid of 7×7 green laser points on the FOV and the scene was recorded using a monochrome high-speed camera. The optical design of the laser projection system lead to laser beams that were divergent. Therefore, the distance between any two laser points was a function of the working distance. To account for this factor, the horizontal calibration was developed based on two different sets of benchtop recordings. In the first set a calibrated grid paper was used as the target surface, while in the second set a white paper was used instead. The working distance was systematically changed from 5 mm to 35 mm in 1-mm increments for both sets. Recordings from the first set were used to determine the mm-distance between laser points at each working distance. The second set was used for learning the trajectories of each laser point as a function of the working distance. This step was carried out to account for the effect of the working distance on the horizontal distance between laser points. Finally, different line segments with known mm sizes were recorded at different working distances. These recordings were used for measuring the accuracy of the developed method.
Results: The results from the experiments demonstrated accurate horizontal measurement using the laser-calibrated endoscope.
Conclusion: The proposed method has resolved a challenge toward horizontal calibrated measurements from in-vivo HSV recordings. It is expected that in-vivo horizontal measurements would improve our knowledge from the vocal fold kinematics and help us make direct evaluation of treatment outcome, e.g. the effect of therapy on lesion size.