Subsequently a comprehensive literature search was conducted to investigate the general principles of stroboscopic imaging from primary sources. Talbot made no reference to stroboscopy in designing his experiments, and the notion of persistence of vision is not applicable to stroboscopic motion. Instead, two visual phenomena play critical roles: 1 the flicker-free perception of light and 2 the perception of apparent motion. The critical visual phenomena are the flicker-free perception of light intensity and the perception of apparent motion from sampled images. A complete understanding of how laryngeal stroboscopy works will aid in better interpreting clinical findings during voice assessment.
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This paper summarizes recent technological advancements and insight into the role of stroboscopy in laryngeal imaging. Although stroboscopy has not undergone major technological improvements, recent clarifications have been made to the application of stroboscopic principles to video-based laryngeal imaging. Also recent advances in coupling stroboscopy with high-definition video cameras provide higher spatial resolution of phonatory function.
Studies indicate that interrater reliability of visual stroboscopic assessment varies depending on the laryngeal feature being rated and that only a subset of features may be needed to represent an entire assessment.
High-speed videoendoscopy HSV judgments have been shown to be more sensitive than stroboscopy for evaluating vocal fold phase asymmetry, pointing to the potential of complementing stroboscopy with alternative imaging modalities in hybrid systems.
Stroboscopic imaging continues to play a central role in voice clinics. Although HSV may provide more detailed information about phonatory function, its eventual clinical adoption depends on how remaining practical, technical, and methodological challenges will be met. Laryngeal videostroboscopy continues to be the modality of choice for imaging vocal fold vibration, but technological advancements and HSV research findings are driving increased interest in the clinical adoption of HSV to complement videostroboscopic assessment.
Stroboscopic imaging of vocal fold vibratory function during phonation continues to play a central role in diagnostic, therapeutic, and surgical decisions during the management and treatment of voice disorders. Although sampling rate limitations prevent stroboscopic imaging from capturing cycle-to-cycle details of vocal fold vibratory characteristics, clinicians are able to observe many salient features that cannot be perceived at standard video frame rates.
While newer laryngeal imaging technologies—such as high-speed videoendoscopy HSV , magnetic resonance imaging, and optical coherence tomography [ 1 ]—continue to enhance our ability to better define and quantify complex phonatory mechanisms, the cost effectiveness, ease of use, and synchronized audio and visual feedback provided by videostroboscopic assessment serves to maintain its predominant clinical role in laryngeal imaging.
This paper provides commentary on recent advances and insight into the application of stroboscopic imaging in clinical voice assessment and voice research.
Imaging of rapid vocal fold motion has a long and storied history. Oertel published the earliest application of stroboscopic principles to observe vocal fold vibrations using a revolving disk with equally spaced holes to mechanically shutter a light source [ 2 — 4 ]. Subjects had to match their pitch to the frequency of the rotating disk to enable the production of a sequence of images that was perceived as a slow-motion representation of the vocal fold vibratory cycle.
Today subjects are free to phonate over a wide range of fundamental frequencies that are typically tracked using signals from neck-mounted contact microphones or electroglottograph electrodes. Mehta et al. These two requirements are satisfied in modern videostroboscopic systems [ 6 — 8 ], which integrate stroboscopic principles with video-based technologies. In , Kay Elemetrics now KayPENTAX introduced laryngeal stroboscopy systems that precisely controlled the triggering of light sources so that only one strobe occurred per video field, thereby eliminating artifacts that were previously present due to multiple exposures within each video field [ 6 ].
A detailed discussion of the interaction among strobe rate, video camera rate, and phonatory fundamental frequency is provided in Hillman and Mehta [ 10 ]. No major technical advancements have been made in recent years regarding stroboscopic imaging. Videostroboscopic technologies typically enable two views of periodic vocal fold vibration.
The systems can appear to freeze tissue motion at a selected phase in the periodic vibratory pattern, or they can create an apparent slow-motion view of the periodic vibratory cycles [ 10 ].
The specific implementation of sampling the motion of the vocal folds varies by manufacturer. An alternative method, employed by JEDMED, applies a constant light source but performs stroboscopic sampling by electronically shuttering the image sensor of the camera [ 7 ]. Regardless of method, the flash or shutter durations are sufficiently short to prevent motion blur artifacts in images that may arise due to rapid vocal fold tissue movements that can approach velocities of one meter per second [ 11 ].
Recent advances in coupling stroboscopic systems with high-definition HD video camera sensors provide unprecedented spatial resolution of the vocal fold structures involved in phonatory vibration e. A formal evaluation of HD versus standard-definition video for laryngeal imaging remains to be undertaken, but the significant improvements in image quality associated with HD are expected to enhance clinical diagnostic capabilities.
As with all imaging modalities, though, the extra resolution afforded is only beneficial if the image target fills up a large portion of the video frame. Figure 1 displays a side-by-side comparison of still frames obtained from standard-definition and HD videostroboscopy recordings during sustained phonation.
High-definition systems provide added spatial resolution as compared to standard-definition systems, which exhibit pixelation at high levels of magnification. A selected segment of the vocal fold edge in each exam is magnified 14x to illustrate the increased pixelation that occurs in the standard-definition image. Figure 2 displays one such rating system, the Stroboscopy Evaluation Rating Form, which assesses the following laryngeal properties during phonation:.
Stroboscopy Evaluation Rating Form developed by Poburka [ 13 ], whose interrater reliability was evaluated by Nawka and Konerding [ 15 ].
Continued on following page. The interrater reliability of judging the ten parameters above during stroboscopic imaging has been investigated in a recent study [ 15 ]. Although most of the interval-scaled parameters yielded adequate interrater reliability, the judgments of phase closure, phase symmetry, and regularity exhibited the poorest reliability and calls into question the overall validity of obtaining these parameters.
The two categorically scaled parameters of vertical level and glottal closure were judged so unreliably that it was suggested that their assessment might hold little information [ 15 ]. Interestingly, parameters exhibiting the most reliable judgments—amplitude, vibratory behavior, and edge—were found by Kelley et al [ 16 ] to form a minimal subset of parameters that accounted for most of the variance of all the laryngeal stroboscopic characteristics.
Although it is unclear if clinicians are ready to completely dispense with making judgments of vocal fold phonatory parameters that have questionable reliability, it is hoped that ongoing efforts to assess the validity and reliability of measures will continue to inform the refinement and application of such rating schemes.
As is well known, stroboscopic imaging has inherent limitations due to its sampling technique. The strobe effect can only be produced if the motion being observed is adequately periodic; thus stroboscopy is typically incapable of revealing vocal fold vibratory patterns once dysphonia exceeds a moderate level [ 17 ]. Even when successful, stroboscopy can only provide a highly-averaged visualization of periodic motion that is not sensitive enough to capture cycle-to-cycle variations in vocal fold vibration that have been linked to the degradation in acoustic voice quality measures [ 18 ].
Figure 3 illustrates the differences between HSV and stroboscopic sampling. A dual endoscopy was performed on a vocally healthy speaker that simultaneously captured HSV data at 6, frames per second along with stroboscopic flashes of light triggered once per video field. In contrast, only one videostroboscopic frame comprised of interlacing two consecutive video fields is captured every eight glottal cycles.
Dual rigid endoscopy of a vocally normal speaker sustaining a vowel. Each row of HSV frames depicts one cycle of vocal fold vibration. White boundaries indicate the durations of NTSC video fields, during which one strobe is flashed to capture advancing phases in the glottal cycle. With the phonatory fundamental frequency at Hz, one videostroboscopic frame comprising two fields would be composed every eight cycles. Modified version of Figure Does the loss of information using stroboscopic imaging matter?
One way to answer this question is to ask judges to rate laryngeal features from HSV and videostroboscopy recordings of sustained phonation and compare the ability of each modality to reliably reveal certain features. In a group of healthy speakers, it was found that the reliability of stroboscopic ratings were comparable with similar ratings made on HSV recordings, except for visual judgments of symmetry [ 19 ]. Another study found high intra- and interrater reliability of phase asymmetry using stroboscopy in vocally healthy subjects [ 20 ] and speakers with voice disorders [ 21 ]; however, the validity of stroboscopy-based judgments of phase asymmetry was called into question due to lower correlations with an objective measure of phase asymmetry as compared to HSV-based modalities [ 20 , 21 ].
A case study also points to the need for HSV-based imaging to describe more detailed vocal fold tissue motion during pre- and post-therapy assessment [ 22 ]. These results suggest that, while stroboscopy may be sensitive to certain visual features, the modality may lack the specificity required for adequate judgments to be made.
In a study utilizing HSV of glottic cancer patients, variations in levels of acoustic jitter and shimmer were found to be unrelated to average measures of asymmetry; instead, a significant amount of the variation in acoustic jitter was accounted for by the standard deviation in the symmetry of phase and amplitude across the vibratory cycles [ 18 ].
This result has implications in terms of stroboscopic imaging because the apparently critical cycle-to-cycle variations in tissue vibratory behavior that were shown to be correlated with the degradation of the acoustic signal would not be reliably revealed using videostroboscopy. Further, since stroboscopic video only captures periodic vocal fold motion, it would be capable of only imaging the kind of highly-repetitive asymmetries that do not appear to make a major contribution to disruptions in acoustic sound generation.
Research efforts continue to determine optimal visualizations of voice production mechanisms [ 1 , 23 ]. This result demonstrates the current routine use of stroboscopy by general otolaryngologists. In the pediatric population, stroboscopy continues to form an integral part of diagnostic voice assessment even though obtaining high-quality rigid or flexible endoscopic recordings may be challenging in children [ 25 ].
Moreover, a pediatric vocal fold nodule rating scale has been developed based on videostroboscopic recordings of sustained vowel production [ 26 ]. Recent publications advocate the use of laryngeal stroboscopic assessment to diagnose general hoarseness [ 27 , 28 ], as well as specific pathological conditions, such as organic lesions [ 29 ] and vocal fold scarring [ 30 ].
A clinical practice guideline published by an AAOHNS-sponsored committee recently reiterated that stroboscopy is advisable to evaluate vocal function related to hoarseness [ 28 ].
Even though HSV provides more detailed temporal information about vocal fold kinematics than stroboscopy, the eventual adoption of HSV into clinical practice will depend on the extent to which remaining practical, technical, and methodological challenges can be met. Such HSV-specific challenges include the relatively high cost of current systems, management and processing of large data files, limitations on memory size, potential thermal effects on tissue due to the intense light sources that are required, and a paucity of solid clinical research that demonstrates that HSV significantly improves the diagnosis and management of voice disorders e.
Hybrid HSV-stroboscopy systems could take advantage and complement the outputs of each imaging modality—e. Laryngeal videostroboscopy continues to be the imaging modality of choice by voice clinicians due to its historical use and ability to efficiently capture many salient vocal fold vibratory characteristics.
Because visual and objective assessments of certain laryngeal features can be unreliable using stroboscopic imaging, further research is warranted into the integration of laryngeal high-speed videoendoscopy and other alternate imaging modalities into routine clinical practice to improve the management of voice disorders. Daryush D. Robert E. National Center for Biotechnology Information , U. Author manuscript; available in PMC Dec 1. Mehta , PhD and Robert E.
Hillman , PhD. Author information Copyright and License information Disclaimer. Mehta: ude. Hillman: ude.
Copyright notice. See other articles in PMC that cite the published article. Abstract Purpose of review This paper summarizes recent technological advancements and insight into the role of stroboscopy in laryngeal imaging. Recent findings Videostroboscopic technology Although stroboscopy has not undergone major technological improvements, recent clarifications have been made to the application of stroboscopic principles to video-based laryngeal imaging. Visual stroboscopic assessment Studies indicate that interrater reliability of visual stroboscopic assessment varies depending on the laryngeal feature being rated and that only a subset of features may be needed to represent an entire assessment.
Clinical role Stroboscopic imaging continues to play a central role in voice clinics. Summary Laryngeal videostroboscopy continues to be the modality of choice for imaging vocal fold vibration, but technological advancements and HSV research findings are driving increased interest in the clinical adoption of HSV to complement videostroboscopic assessment.
Keywords: stroboscopy, vocal folds, imaging, larynx, clinical voice assessment. Introduction Stroboscopic imaging of vocal fold vibratory function during phonation continues to play a central role in diagnostic, therapeutic, and surgical decisions during the management and treatment of voice disorders.
Technological advancements Imaging of rapid vocal fold motion has a long and storied history. High-definition videostroboscopy Recent advances in coupling stroboscopic systems with high-definition HD video camera sensors provide unprecedented spatial resolution of the vocal fold structures involved in phonatory vibration e. Open in a separate window. Figure 1. Figure 2. Interrater reliability The interrater reliability of judging the ten parameters above during stroboscopic imaging has been investigated in a recent study [ 15 ].
Comparison of videostroboscopy and high-speed videoendoscopy As is well known, stroboscopic imaging has inherent limitations due to its sampling technique.
Figure 3. Which visualization is better? Diagnostic value of stroboscopy Recent publications advocate the use of laryngeal stroboscopic assessment to diagnose general hoarseness [ 27 , 28 ], as well as specific pathological conditions, such as organic lesions [ 29 ] and vocal fold scarring [ 30 ].
How are the Vocal Folds and Larynx Examined?
Video laryngeal stroboscopy VLS is a procedure done to evaluate the motion of the vocal cords. It allows the physician to tell the difference between different lesions of the vocal cords that can affect the voice. It is used when there is a complaint of a voice disorder such as hoarseness or loss of voice. Your Surgeon will discuss this recommendation with you, and why it is being recommended prior to performing the test, to ensure it is done as comfortably as possible for you and your child. The procedure is done with the child awake and in the sitting position. An anesthetic spray is used in the nose to numb the nasal passage and throat to minimize discomfort.
Key Glossary Terms. Rigid Laryngoscopy An examination of the voice box in which a rigid telescope is used; this examination provides the clearest magnified detail of the voice box, but the patient is unable to speak or sing during the exam. Flexible Laryngoscopy An examination of the voice box in which a flexible fiberoptic scope is used; this examination allows the physician to view the voice box in action i. Stroboscopy An examination in which a strobe light is combined with rigid or flexible laryngoscopy, allowing an examination of vocal fold vibration and vocal fold closure.