Dimitar D. Deliyski

Clinical implementation of laryngeal high-speed videoendoscopy: Challenges and evolution

High-speed videoendoscopy (HSV) captures the true intracycle vibratory behavior of the vocal folds, which allows for overcoming the limitations of videostroboscopy for more accurate objective quantification methods. However, the commercial HSV systems have not gained widespread clinical adoption because of remaining technical and methodological limitations and an associated lack of information regarding the validity, practicality, and clinical relevance of HSV. The purpose of this article is to summarize the practical, technological and methodological challenges we have faced, to delineate the advances we have made, and to share our current vision of the necessary steps towards developing HSV into a robust tool. This tool will provide further insights into the biomechanics of laryngeal sound production, as well as enable more accurate functional assessment of the pathophysiology of voice disorders leading to refinements in the diagnosis and management of vocal fold pathology. The original contributions of this paper are the descriptions of our color high-resolution HSV integration, the methods for facilitative playback and HSV dynamic segmentation, and the ongoing efforts for implementing HSV in phonomicrosurgery, as well as the analysis of the challenges and prospects for the clinical implementation of HSV, additionally supported by references to previously reported data.

State of the art laryngeal imaging: research and clinical implications.

Purpose of reviewThis study provides a review of the latest advances in videostroboscopy, videokymography and high-speed videoendoscopy, and outlines the development of new laryngeal imaging modalities based on optical coherence tomography, laser-depth kymography, and magnetic resonance imaging (MRI), published in the past 2 years. Recent findingsVideostroboscopy and videokymography: Image quality has improved and several image processing and measurement techniques have been published.High-speed videoendoscopy: Significant progress has been made through increased sensitivity and frame rates of the cameras, and the development of facilitative playbacks, phonovibrography and several image segmentation and measurement methods. Clinical evidence was presented through applications in phonosurgery, comparisons with videostroboscopy, normative data, and better understanding of voice production.Optical coherence tomography: Latest developments allow the capture of dynamic high-resolution cross-sectional images of the vibrating vocal fold mucosa during phonation.Depth kymography: New laser technique allowing recording of the vertical movements of the vocal folds during phonation in calibrated spatial values.Laryngeal magnetic resonance: New methods allow high-resolution imaging of laryngeal tissue microstructure, or measuring of dynamic laryngeal structures during phonation. SummaryThe endoscopic laryngeal imaging techniques have made significant advances increasing their clinical value, whereas techniques providing new types of potentially clinically relevant information have emerged.

Voice Production Mechanisms following Phonosurgical Treatment of Early Glottic Cancer

Objectives: Although near-normal conversational voices can be achieved with the phonosurgical management of early glottic cancer, there are still acoustic and aerodynamic deficits in vocal function that must be better understood to help further optimize phonosurgical interventions. Stroboscopic assessment is inadequate for this purpose. Methods: A newly developed color high-speed videoendoscopy (HSV) system that included time-synchronized recordings of the acoustic signal was used to perform a detailed examination of voice production mechanisms in 14 subjects. Digital image processing techniques were used to quantify glottal phonatory function and to delineate relationships between vocal fold vibratory properties and acoustic perturbation measures. Results: The results for multiple measurements of vibratory asymmetry showed that 31% to 62% of subjects displayed higher-than-normal average values, whereas the mean values for glottal closure duration (open quotient) and periodicity of vibration fell within normal limits. The average HSV-based measures did not correlate significantly with the acoustic perturbation measures, but moderate correlations were exhibited between the acoustic measures and the SDs of the HSV-based parameters. Conclusions: The use of simultaneous, time-synchronized HSV and acoustic recordings can provide new insights into postoperative voice production mechanisms that cannot be obtained with stroboscopic assessment.

Regression Tree Approach to Studying Factors Influencing Acoustic Voice Analysis

Multiple factors influence voice quality measurements (VQM) obtained during an acoustic voice assessment including: gender, intrasubject variability, microphone, environmental noise (type and level), data acquisition (DA) system, and analysis software. This study used regression trees to investigate the order and relative importance of these factors on VQM including interaction effects of the factors and how the outcome differs when the acoustic environment is controlled for noise. Twenty normophonic participants provided 20 voice samples each, which were recorded synchronously on five DA systems combined with six different microphones. The samples were mixed with five noise types at eight signal-to-noise ratio (SNR) levels. The resulting 80,000 audio samples were analyzed for fundamental frequency (F₀), jitter and shimmer using three software analysis systems: MDVP, PRAAT, and TF32 (CSpeech). Fifteen regression trees and their Variable Importance Measures were utilized to analyze the data. The analyses confirmed that all of the factors listed above were influential. The results suggest that gender, intrasubject variability, and microphone were significant influences on F₀. Software systems and gender were highly influential on measurements of jitter and shimmer. Environmental noise was shown to be the prominent factor that affects VQM when SNR levels are below 30 dB.

Perturbation Measures of Voice: A Comparative Study between Multi-Dimensional Voice Program and Praat

Background/Aims: Frequency and amplitude perturbations are inherent in voice acoustic signals. The assessment of voice perturbation is influenced by several factors, including the type of recording equipment used and the measurement extraction algorithm applied. In the present study, perturbation measures provided by two computer systems (a purpose-built professional voice analysis apparatus and a personal computer-based system for acoustic voice assessment) and two computer programs (Multi-Dimensional Voice Program and Praat) were compared. Methods: Correlations and inferential statistics for seven perturbation measures (absolute jitter, percent jitter, relative average perturbation, pitch perturbation quotient, shimmer in decibels, percent shimmer, and amplitude perturbation quotient) in 50 subjects with various voice disorders are presented. Results: Results indicate statistically significant differences between the two systems and programs, with the Multi-Dimensional Voice Program yielding consistently higher measures than Praat. Furthermore, correlation analyses show weak to moderate proportional relationships between the two systems and weak to strong proportional relationships between the two programs. Conclusion: Based on the literature and the proportional relationships and differences between the two systems and programs under consideration in this study, one can state that one can hardly compare frequency perturbation outcomes across systems and programs and amplitude perturbation outcomes across systems.

Influence of sampling rate on accuracy and reliability of acoustic voice analysis

It is universally recognized that sampling rate (FS) influences the reliability and validity of acoustic voice measurements; however, an exact relationship has not been determined. The purpose of this experiment was to investigate the influence of FS on acoustic voice quality measurements, while considering the influences of gender, intra-subject variability, microphone, environmental noise, data acquisition hardware, and analysis software as balancing factors. The impact of FS, from 44.1 kHz to 10 kHz, was explored by analyzing 864 000 measures of fundamental frequency, jitter, and shimmer, using three software analysis systems: MDVP, TF32, and PRAAT. Results suggest that the recommended, acceptable, and critical FS for acoustic voice analysis are above 26 kHz, above 19 kHz, and 12 kHz, respectively. Thus, voice samples captured above 26 kHz can be used for data analysis and compared without introducing error due to FS.

High-speed videoendoscopic analysis of relationships between cepstral-based acoustic measures and voice production mechanisms in patients undergoing phonomicrosurgery

Objectives: There is increased interest in using cepstral-based acoustic measures for objective clinical voice assessment because of their apparent advantages over more time-honored methods, but there is a paucity of information about how these newer measures relate to underlying phonatory mechanisms. Methods: We investigated the relationships between the acoustic cepstral peak magnitude (CPM) and high-speed videoendoscopy (HSV)–based measures of vocal fold phonatory function in 20 subjects who underwent phonomicrosurgery for vocal fold lesions. Acoustic and imaging data were acquired during sustained vowel phonation before and after surgery. Results: The changes in the measures between presurgical and postsurgical assessments showed that the CPM correlated significantly with an HSV-based measure combining fundamental frequency deviation and average speed quotient (r = 0.70; p < 0.001) in a multiple linear regression, and that the variation in the CPM could also be attributed to trading relationships between the HSV-based measures of vibratory phase asymmetry and glottal closure. Conclusions: These initial results demonstrate that the clinical utility of cepstral-based measures can be enhanced by a better understanding of how these acoustic measures relate to underlying phonatory mechanisms. The CPM seems to integrate information about aperiodicity in vocal fold vibration, the relative speed of glottal closure, and estimates of glottal noise generation.

Vocal fold mucus aggregation in vocally normal speakers

Vocal fold mucus aggregation is common in persons with voice disorders. The normality of vocal fold mucus aggregation in vocally normal speakers is not known. The purpose of this study was to preliminarily ascertain the presence, type, thickness, location, and pooling of mucus aggregation in vocally normal speakers. An additional aim was to evaluate whether the features of mucus aggregation are more easily identified using stroboscopy or high-speed videoendoscopy (HSV). These aims were accomplished by visually rating a systematically collected database of stroboscopy and HSV recordings from 52 normophonic speakers. Results revealed 97% of normophonic speakers presented with visible mucus aggregation. Statistically significant differences were found for judgments of HSV compared to stroboscopy on the parameters of type 1 mucus, not apparent and mild thickness, not apparent pooling, and all three locations. Two main conclusions can be drawn from this study: 1) normophonic speakers commonly have mucus aggregation and 2) mucus aggregation is identified more often through stroboscopy than HSV.

Analysis of vocal folds movement in high speed videoendoscopy based on level set segmentation and image registration

Computer analysis of high-speed videoendoscopy (HSV) recordings is becoming increasingly useful in functional evaluation of vocal fold pathology. In this work we present two new approaches for the vocal fold HSV-based analysis that have not been previously reported. First, segmentation of vocal fold edges is performed in our method using the level set algorithm. Second, having two vocal fold contours (for two images) we find point-to-point matching of them using the image registration method based on B-spline free form deformation. Presented results from analysis of normal vocal folds and folds after laser treatment confirm usefulness of the method.

Experimental investigation on minimum frame rate requirements of high-speed videoendoscopy for clinical voice assessment ☆

This study investigated the impact of high-speed videoendoscopy (HSV) frame rates on the assessment of nine clinically-relevant vocal-fold vibratory features. Fourteen adult patients with voice disorder and 14 adult normal controls were recorded using monochromatic rigid HSV at a rate of 16000 frames per second (fps) and spatial resolution of 639×639 pixels. The 16000-fps data were downsampled to 16 other rate denominations. Using paired comparisons design, nine common clinical vibratory features were visually compared between the downsampled and the original images. Three raters reported the thresholds at which: (1) a detectable difference between the two videos was first noticed, and (2) differences between the two videos would result in a change of clinical rating. Results indicated that glottal edge, mucosal wave magnitude and extent, aperiodicity, contact and loss of contact of the vocal folds were the vibratory features most sensitive to frame rate. Of these vibratory features, the glottal edge was selected for further analysis, due to its higher rating reliability, universal prevalence and consistent definition. Rates of 8000 fps were found to be free from visually-perceivable feature degradation, and for rates of 5333 fps, degradation was minimal. For rates of 4000 fps and higher, clinical assessments of glottal edge were not affected. Rates of 2000 fps changed the clinical ratings in over 16% of the samples, which could lead to inaccurate functional assessment.