Qualification of a quantitative laryngeal imaging system using videostroboscopy and videokymography

Abstract

Objectives: We sought to determine whether full-cycle glottal width measurements could be obtained with a quantitative laryngeal imaging system using videostroboscopy, and whether glottal width and vocal fold length measurements were repeatable and reliable.

Methods: Synthetic vocal folds were phonated on a laboratory bench, and dynamic images were obtained in repeated trials by use of videostroboscopy and videokymography (VKG) with an imaging system equipped with a 2-point laser projection device for measuring absolute dimensions. Video images were also obtained with an industrial videoscope system with a built-in laser measurement capability. Maximum glottal width and vocal fold length were compared among these 3 methods.

Results: The average variation in maximum glottal width measurements between stroboscopic data and VKG data was 3.10%. The average variations in width measurements between the clinical system and the industrial system were 1.93% (stroboscopy) and 3.49% (VKG). The variations in vocal fold length were similarly small. The standard deviations across trials were 0.29 mm for width and 0.48 mm for length (stroboscopy), 0.18 mm for width (VKG), and 0.25 mm for width and 0.84 mm for length (industrial).

Conclusions: For stable, periodic vibration, the full extent of the glottal width can be reliably measured with the quantitative videostroboscopy system.

Fig 1

Schematic of experimental setup.

Fig 2

Design of 2-point laser projection device. A) Schematic of beam-splitting and reflection optics. B) Optical bench breadboard shows close-up of birefringent crystal and right angle prism mirror.

Fig 3

Equipment used in experiment. A) KayPENTAX model 9106 rigid endoscope with 2-point laser projection system attached. (Endoscope rod is on left; laser optics cannula is on right.) B) Rubber glottis-shaped orifice plate simulating human vocal fold geometry. Arrow indicates synthetic rubber vocal folds.

Fig 4

Sample videostroboscopy frame shows automatic dot distance and glottal width detection.

Fig 5

Plot of frame-by-frame analysis of 4 seconds (120 frames) of stroboscopy video with 2-point laser projection system used to calculate absolute glottal width and absolute length of synthetic vocal folds. Circled data points are maximum glottal widths in each cycle used to calculate multicycle average.

Fig 6

Results of frame-by-frame analysis of 4 seconds (120 frames) of video obtained with Karl Storz TPX videoscope system with LaserTrue used to calculate absolute glottal width and absolute length of synthetic vocal folds. Shutter speed is 0.5 ms. A) Cyclical plots of glottal width and vocal fold length versus frame number. Circled data points are results of automatic glottis detection software that were verified by visual inspection. Data points above 5 mm are errors in glottal detection software, and were not used to calculate multicycle average. B) Example of glottal detection error due to blurred picture.

Fig 7

Glottal width detection using videokymography. A) Standard-mode frame of simulated vocal folds shows 2-mmspaced dots from 2-laser projection system. B) Sample frame of high-speed videokymography data used to calculate maximum glottal width of 4.43 mm.