Publications

    H. Ghasemzadeh, D. D. Deliyski, D. S. Ford, J. B. Kobler, R. E. Hillman, and D. D. Mehta, “Method for vertical calibration of laser-projection transnasal fiberoptic high-speed videoendoscopy,” Journal of Voice, In Press. Publisher's VersionAbstract
    The ability to provide absolute calibrated measurement of the laryngeal structures during phonation is of paramount importance to voice science and clinical practice. Calibrated three-dimensional measurement could provide essential information for modeling purposes, for studying the developmental aspects of vocal fold vibration, for refining functional voice assessment and treatment outcomes evaluation, and for more accurate staging and grading of laryngeal disease. Recently, a laser-calibrated transnasal fiberoptic endoscope compatible with high-speed videoendoscopy (HSV) and capable of providing three-dimensional measurements was developed. The optical principle employed 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, such that (after calibration) the position of each laser point within the FOV encodes the vertical distance from the tip of the endoscope to the laryngeal tissues. The purpose of this study was to develop a precise method for vertical calibration of the endoscope. Investigating the position of the laser points showed that, besides the vertical distance, they also depend on the parameters of the lens coupler, including the FOV position within the image frame and the rotation angle of the endoscope. The presented automatic calibration method was developed to compensate for the effect of these parameters. Statistical image processing and pattern recognition were used to detect the FOV, the center of FOV, and the fiducial marker. This step normalizes the HSV frames to a standard coordinate system and removes the dependence of the laser-point positions on the parameters of the lens coupler. Then, using a statistical learning technique, a calibration protocol was developed to model the trajectories of all laser points as the working distance was varied. Finally, a set of experiments was conducted to measure the accuracy and reliability of every step of the procedure. The system was able to measure absolute vertical distance with mean percent error in the range of 1.7% to 4.7%, depending on the working distance.
    M. Motie-Shirazi, et al., “Toward development of a vocal fold contact pressure probe: Sensor characterization and validation using synthetic vocal fold models,” Applied Sciences, vol. 9, no. 15, pp. 3002, 2019. Publisher's VersionAbstract
    Excessive vocal fold collision pressures during phonation are considered to play a primary role in the formation of benign vocal fold lesions, such as nodules. The ability to accurately and reliably acquire intraglottal pressure has the potential to provide unique insights into the pathophysiology of phonotrauma. Difficulties arise, however, in directly measuring vocal fold contact pressures due to physical intrusion from the sensor that may disrupt the contact mechanics, as well as difficulty in determining probe/sensor position relative to the contact location. These issues are quantified and addressed through the implementation of a novel approach for identifying the timing and location of vocal fold contact, and measuring intraglottal and vocal fold contact pressures via a pressure probe embedded in the wall of a hemi-laryngeal flow facility. The accuracy and sensitivity of the pressure measurements are validated against ground truth values. Application to in vivo approaches are assessed by acquiring intraglottal and VF contact pressures using a synthetic, self-oscillating vocal fold model in a hemi-laryngeal configuration, where the sensitivity of the measured intraglottal and vocal fold contact pressure relative to the sensor position is explored.
    M. E. Powell, D. D. Deliyski, R. E. Hillman, S. M. Zeitels, J. A. Burns, and D. D. Mehta, “Comparison of videostroboscopy to stroboscopy derived from high-speed videoendoscopy for evaluating patients with vocal fold mass lesions,” American Journal of Speech-Language Pathology, vol. 25, pp. 576-589, 2016. Publisher's VersionAbstract

    indirect physiological signal to predict the phase of the vocal fold vibratory cycle for sampling. Simulated stroboscopy (SS) extracts the phase of the glottal cycle directly from the changing glottal area in the high-speed videoendoscopy (HSV) image sequence. The purpose of this study is to determine the reliability of SS relative to VS for clinical assessment of vocal fold vibratory function in patients with mass lesions.

    Methods VS and SS recordings were obtained from 28 patients with vocal fold mass lesions before and after phonomicrosurgery and 17 controls who were vocally healthy. Two clinicians rated clinically relevant vocal fold vibratory features using both imaging techniques, indicated their internal level of confidence in the accuracy of their ratings, and provided reasons for low or no confidence.

    Results SS had fewer asynchronous image sequences than VS. Vibratory outcomes were able to be computed for more patients using SS. In addition, raters demonstrated better interrater reliability and reported equal or higher levels of confidence using SS than VS.

    Conclusion Stroboscopic techniques on the basis of extracting the phase directly from the HSV image sequence are more reliable than acoustic-based VS. Findings suggest that SS derived from high-speed videoendoscopy is a promising improvement over current VS systems.

    D. D. Mehta, D. D. Deliyski, T. F. Quatieri, and R. E. Hillman, “Automated measurement of vocal fold vibratory asymmetry from high-speed videoendoscopy recordings,” Journal of Speech, Language, and Hearing Research, vol. 54, no. 1, pp. 47-54, 2011. Publisher's VersionAbstract

    Purpose: In prior work, a manually derived measure of vocal fold vibratory phase asymmetry correlated to varying degrees with visual judgments made from laryngeal high-speed videoendoscopy (HSV) recordings. This investigation extended this work by establishing an automated HSV-based framework to quantify 3 categories of vocal fold vibratory asymmetry. Method: HSV-based analysis provided for cycle-to-cycle estimates of left-right phase asymmetry, left-right amplitude asymmetry, and axis shift during glottal closure for 52 speakers with no vocal pathology producing comfortable and pressed phonation. An initial cross-validation of the automated left-right phase asymmetry measure was performed by correlating the measure with other objective and subjective assessments of phase asymmetry. Results: Vocal fold vibratory asymmetry was exhibited to a similar extent in both comfortable and pressed phonations. The automated measure of left-right phase asymmetry strongly correlated with manually derived measures and moderately correlated with visual-perceptual ratings. Correlations with the visual-perceptual ratings remained relatively consistent as the automated measure was derived from kymograms taken at different glottal locations. Conclusions: An automated HSV-based framework for the quantification of vocal fold vibratory asymmetry was developed and initially validated. This framework serves as a platform for investigating relationships between vocal fold tissue motion and acoustic measures of voice function.

    D. D. Mehta, M. Zañartu, T. F. Quatieri, D. D. Deliyski, and R. E. Hillman, “Investigating acoustic correlates of human vocal fold vibratory phase asymmetry through modeling and laryngeal high-speed videoendoscopy,” The Journal of the Acoustical Society of America, vol. 130, pp. 3999-4009, 2011.Abstract

    Vocal fold vibratory asymmetry is often associated with inefficient sound production through its impact on source spectral tilt. This association is investigated in both a computational voice production model and a group of 47 human subjects. The model provides indirect control over the degree of left-right phase asymmetry within a nonlinear source-filter framework, and high-speed videoendoscopy provides in vivo measures of vocal fold vibratory asymmetry. Source spectral tilt measures are estimated from the inverse-filtered spectrum of the simulated and recorded radiated acoustic pressure. As expected, model simulations indicate that increasing left-right phase asymmetry induces steeper spectral tilt. Subject data, however, reveal that none of the vibratory asymmetry measures correlates with spectral tilt measures. Probing further into physiological correlates of spectral tilt that might be affected by asymmetry, the glottal area waveform is parameterized to obtain measures of the open phase (open/plateau quotient) and closing phase (speed/closing quotient). Subjects' left-right phase asymmetry exhibits low, but statistically significant, correlations with speed quotient (r=0.45) and closing quotient (r=-0.39). Results call for future studies into the effect of asymmetric vocal fold vibration on glottal airflow and the associated impact on voice source spectral properties and vocal efficiency.

    D. D. Mehta, D. D. Deliyski, S. M. Zeitels, T. F. Quatieri, and R. E. Hillman, “Voice production mechanisms following phonosurgical treatment of early glottic cancer,” Annals of Otology, Rhinology, and Laryngology, vol. 119, pp. 1-9, 2010. Publisher's VersionAbstract

    Objectives: Although near-normal conversational voices can be achieved with the phonosurgical management of earlyglottic cancer, there are still acoustic and aerodynamic deficits in vocal function that must be better understood to helpfurther optimize phonosurgical interventions. Stroboscopic assessment is inadequate for this purpose.Methods: A newly developed color high-speed videoendoscopy (HSV) system that included time-synchronized recordingsof 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 betweenvocal fold vibratory properties and acoustic perturbation measures.Results: The results for multiple measurements of vibratory asymmetry showed that 31% to 62% of subjects displayedhigher-than-normal average values, whereas the mean values for glottal closure duration (open quotient) and periodicityof vibration fell within normal limits. The average HSV-based measures did not correlate significantly with the acousticperturbation measures, but moderate correlations were exhibited between the acoustic measures and the SDs of the HSVbasedparameters.Conclusions: The use of simultaneous, time-synchronized HSV and acoustic recordings can provide new insights intopostoperative voice production mechanisms that cannot be obtained with stroboscopic assessment.