Clinically evaluated procedure for the reconstruction of vocal fold vibrations from endoscopic digital high-speed videos

Relationship Between Acoustic Voice Onset and Offset and Selected Instances of Oscillatory Onset and Offset in Young Healthy Men and Women

OBJECTIVE

This study aimed to investigate the relationship between (1) onset of the acoustic signal (X_1a) and prephonatory phases associated with oscillatory onset and (2) offset of the acoustic signal (X_2a) with the postphonatory events associated with oscillatory offset across vocally healthy adults.

SUBJECTS AND METHODS

High-speed videoendoscopy was captured simultaneously with the acoustic signal during repeated production of /hi.hi.hi/ at typical pitch and loudness from 56 vocally healthy adults (aged 20-42 years; 21 men, 35 women). The relationships between the acoustic sound pressure signal and oscillatory onset and offset events from the glottal area waveforms (GAWs) were statistically investigated using a multivariate linear regression analysis.

RESULTS

The X_1a is a significant predictor of the onset of first oscillatory motion (X_1g) and onset of sustained oscillations (X_2g). X_1a as well as gender are significant predictors of the first medial contact of the vocal folds (X_1.5g). The X_2a is a significant predictor of the first instance of oscillatory offset (X_3g), first instance of incomplete glottal closure (X_3.5g), and complete cessation of (vocal fold) oscillatory motion (X_4g).

CONCLUSIONS

The acoustic signal onset is closely related to the X_1.5g, but the latency between these events is longer for women compared to men. The X_2a occurs immediately after incomplete glottal adduction. The emerging normative group latencies between the onset and offset of the acoustic and the GAW from this study appear promising for future investigations.

The influence of water resistance therapy on vocal fold vibration: a high-speed digital imaging study

PURPOSE

This study investigated the influence of tube phonation into water on vocal fold vibration.

METHOD

Eight participants were analyzed via high-speed digital imaging while phonating into a silicon tube with the free end submerged into water. Two test sequences were studied: (1) phonation pre, during, and post tube submerged 5 cm into water; and (2) phonation into tube submerged 5 cm, 10 cm, and 18 cm into water. Several glottal area parameters were calculated using phonovibrograms.

RESULTS

The results showed individual differences. However, certain trends were possible to identify based on similar results found for the majority of participants. Amplitude-to-length ratio, harmonic-to-noise ratio, and spectral flatness (derived from glottal area) decreased for all tube immersion depths, while glottal closing quotient increased for 10 cm immersion and contact quotient for 18 cm immersion. Closed quotient decreased during phonation into the tube at 5 cm depth, and jitter decreased during and after it.

CONCLUSION

Results suggest that the depth of tube submersion appears to have an effect on phonation. Shallow immersion seems to promote smoother and more stable phonation, while deeper immersion may involve increased respiratory and glottal effort to compensate for the increased supraglottal resistance. This disparity, which is dependent upon the degree of flow resistance, should be considered when choosing treatment exercises for patients with various diagnoses, namely hyperfunctional or hypofunctional dysphonia.

Vibratory onset and offset times in children: A laryngeal imaging study

OBJECTIVES

The aim of the study was to evaluate the differences in vibratory onset and offset times across age (adult males, adult females, and children) and waveform types (total glottal area waveform, left glottal area waveform, and right glottal area waveform) using high-speed videoendoscopy.

METHODS

In this prospective study, vibratory onset and offset times were evaluated in a total of 86 participants. Forty-three children (23 girls, 18 boys) between 5 and 11 years and 43 gender matched vocally normal young adults (23 females and 18 males) in the age range (21-45 years) were recruited. Vibratory onset and offset times were calculated in milliseconds from the total, left, and right Glottal Area Waveform (GAW). A two-factor analysis of variance was used to compare the means among the subject groups (children, adult male, and adult female) and waveform type (total GAW, left GAW, right GAW) for onset and offset variables. Post hoc analyses were performed using the Fishers Least Significant Different test with Bonferroni correction for multiple comparisons.

RESULTS

Children exhibited significantly shorter vibratory onset and offset times compared to adult males and females. Differences in vibratory onset and offset times were not statistically significant between adult males and females. Across all waveform types (i.e. total GAW, left GAW, and right GAW), no statistical significance was observed among the subject groups.

CONCLUSION

This is the first study reporting vibratory onset and offset times in the pediatric population. The study findings lay the foundation for the development of a large age- and gender-based database of the pediatric population to aid the study of the effects of maturation of vocal fold vibration in adulthood. The findings from this study may also provide the basis for evaluating the impact of numerous lesions on tissue pliability, and thereby has potential utility for the clinical differentiation of various lesions.

Evaluation of Analytical Modeling Functions for the Phonation Onset Process

The human voice originates from oscillations of the vocal folds in the larynx. The duration of the voice onset (VO), called the voice onset time (VOT), is currently under investigation as a clinical indicator for correct laryngeal functionality. Different analytical approaches for computing the VOT based on endoscopic imaging were compared to determine the most reliable method to quantify automatically the transient vocal fold oscillations during VO. Transnasal endoscopic imaging in combination with a high-speed camera (8000 fps) was applied to visualize the phonation onset process. Two different definitions of VO interval were investigated. Six analytical functions were tested that approximate the envelope of the filtered or unfiltered glottal area waveform (GAW) during phonation onset. A total of 126 recordings from nine healthy males and 210 recordings from 15 healthy females were evaluated. Three criteria were analyzed to determine the most appropriate computation approach: (1) reliability of the fit function for a correct approximation of VO; (2) consistency represented by the standard deviation of VOT; and (3) accuracy of the approximation of VO. The results suggest the computation of VOT by a fourth-order polynomial approximation in the interval between 32.2 and 67.8% of the saturation amplitude of the filtered GAW.

Comprehensive, Population-Based Sensitivity Analysis of a Two-Mass Vocal Fold Model

Previous vocal fold modeling studies have generally focused on generating detailed data regarding a narrow subset of possible model configurations. These studies can be interpreted to be the investigation of a single subject under one or more vocal conditions. In this study, a broad population-based sensitivity analysis is employed to examine the behavior of a virtual population of subjects and to identify trends between virtual individuals as opposed to investigating a single subject or model instance. Four different sensitivity analysis techniques were used in accomplishing this task. Influential relationships between model input parameters and model outputs were identified, and an exploration of the model’s parameter space was conducted. Results indicate that the behavior of the selected two-mass model is largely dominated by complex interactions, and that few input-output pairs have a consistent effect on the model. Results from the analysis can be used to increase the efficiency of optimization routines of reduced-order models used to investigate voice abnormalities. Results also demonstrate the types of challenges and difficulties to be expected when applying sensitivity analyses to more complex vocal fold models. Such challenges are discussed and recommendations are made for future studies.

Voice pathology classification based on High-Speed Videoendoscopy

This work presents a method for automatical and objective classification of patients with healthy and pathological vocal fold vibration impairments using High-Speed Videoendoscopy of the larynx. We used an image segmentation and extraction of a novel set of numerical parameters describing the spatio-temporal dynamics of vocal folds to classification according to the normal and pathological cases and achieved 73,3% cross-validation classification accuracy. This approach is promising to develop an automatic diagnosis tool of voice disorders.

A generalized procedure for analyzing sustained and dynamic vocal fold vibrations from laryngeal high-speed videos using phonovibrograms

OBJECTIVE

This work presents a computer-based approach to analyze the two-dimensional vocal fold dynamics of endoscopic high-speed videos, and constitutes an extension and generalization of a previously proposed wavelet-based procedure. While most approaches aim for analyzing sustained phonation conditions, the proposed method allows for a clinically adequate analysis of both dynamic as well as sustained phonation paradigms.

MATERIALS AND METHODS

The analysis procedure is based on a spatio-temporal visualization technique, the phonovibrogram, that facilitates the documentation of the visible laryngeal dynamics. From the phonovibrogram, a low-dimensional set of features is computed using a principle component analysis strategy that quantifies the type of vibration patterns, irregularity, lateral symmetry and synchronicity, as a function of time. Two different test bench data sets are used to validate the approach: (I) 150 healthy and pathologic subjects examined during sustained phonation. (II) 20 healthy and pathologic subjects that were examined twice: during sustained phonation and a glissando from a low to a higher fundamental frequency. In order to assess the discriminative power of the extracted features, a Support Vector Machine is trained to distinguish between physiologic and pathologic vibrations. The results for sustained phonation sequences are compared to the previous approach. Finally, the classification performance of the stationary analyzing procedure is compared to the transient analysis of the glissando maneuver.

RESULTS

For the first test bench the proposed procedure outperformed the previous approach (proposed feature set: accuracy: 91.3%, sensitivity: 80%, specificity: 97%, previous approach: accuracy: 89.3%, sensitivity: 76%, specificity: 96%). Comparing the classification performance of the second test bench further corroborates that analyzing transient paradigms provides clear additional diagnostic value (glissando maneuver: accuracy: 90%, sensitivity: 100%, specificity: 80%, sustained phonation: accuracy: 75%, sensitivity: 80%, specificity: 70%).

CONCLUSIONS

The incorporation of parameters describing the temporal evolvement of vocal fold vibration clearly improves the automatic identification of pathologic vibration patterns. Furthermore, incorporating a dynamic phonation paradigm provides additional valuable information about the underlying laryngeal dynamics that cannot be derived from sustained conditions. The proposed generalized approach provides a better overall classification performance than the previous approach, and hence constitutes a new advantageous tool for an improved clinical diagnosis of voice disorders.

An automatic method to detect and track the glottal gap from high speed videoendoscopic images

BACKGROUND

The image-based analysis of the vocal folds vibration plays an important role in the diagnosis of voice disorders. The analysis is based not only on the direct observation of the video sequences, but also in an objective characterization of the phonation process by means of features extracted from the recorded images. However, such analysis is based on a previous accurate identification of the glottal gap, which is the most challenging step for a further automatic assessment of the vocal folds vibration.

METHODS

In this work, a complete framework to automatically segment and track the glottal area (or glottal gap) is proposed. The algorithm identifies a region of interest that is adapted along time, and combine active contours and watershed transform for the final delineation of the glottis and also an automatic procedure for synthesize different videokymograms is proposed.

RESULTS

Thanks to the ROI implementation, our technique is robust to the camera shifting and also the objective test proved the effectiveness and performance of the approach in the most challenging scenarios that it is when exist an inappropriate closure of the vocal folds.

CONCLUSIONS

The novelties of the proposed algorithm relies on the used of temporal information for identify an adaptive ROI and the use of watershed merging combined with active contours for the glottis delimitation. Additionally, an automatic procedure for synthesize multiline VKG by the identification of the glottal main axis is developed.

Laryngeal High-Speed Videoendoscopy: Rationale and Recommendation for Accurate and Consistent Terminology

PURPOSE

The authors discuss the rationale behind the term laryngeal high-speed videoendoscopy to describe the application of high-speed endoscopic imaging techniques to the visualization of vocal fold vibration.

METHOD

Commentary on the advantages of using accurate and consistent terminology in the field of voice research is provided. Specific justification is described for each component of the term high-speed videoendoscopy, which is compared and contrasted with alternative terminologies in the literature.

RESULTS

In addition to the ubiquitous high-speed descriptor, the term endoscopy is necessary to specify the appropriate imaging technology and distinguish among modalities such as ultrasound, magnetic resonance imaging, and nonendoscopic optical imaging. Furthermore, the term video critically indicates the electronic recording of a sequence of optical still images representing scenes in motion, in contrast to strobed images using high-speed photography and non-optical high-speed magnetic resonance imaging. High-speed videoendoscopy thus concisely describes the technology and can be appended by the desired anatomical nomenclature such as laryngeal.

CONCLUSIONS

Laryngeal high-speed videoendoscopy strikes a balance between conciseness and specificity when referring to the typical high-speed imaging method performed on human participants. Guidance for the creation of future terminology provides clarity and context for current and future experiments and the dissemination of results among researchers.

Spatiotemporal Quantification of Vocal Fold Vibration After Exposure to Superficial Laryngeal Dehydration: A Preliminary Study

OBJECTIVES

The aim of the study was to evaluate the effects of a superficial laryngeal dehydration challenge on vocal fold vibration in young healthy adults using high-speed video imaging.

SUBJECTS AND METHODS

In this prospective study, the effects of a 60-minute superficial laryngeal dehydration challenge on spatial (speed quotient, amplitude quotient) and temporal measures (jitter percentage, vibratory onset time) of vocal fold vibration and phonation threshold pressure (PTP) were evaluated in 10 (male = 4, female = 6) vocally normal adults (21-29 years). All measures except the vibratory onset time were measured at the 10 (low) and 80 (high) percent level of their pitch range. The vibratory onset time was obtained at habitual pitch and loudness level. Superficial laryngeal dehydration was induced by oral breathing in low ambient humidity. Prechallenge and postchallenge differences were statistically investigated using t tests with Bonferroni correction.

RESULTS

The speed quotient at low-pitch phonation significantly decreased after oral breathing of low ambient humidity. Other spatiotemporal measures and PTP at low and high pitch were not significant after challenge.

CONCLUSIONS

Results from this initial study have implications for the use of high-speed video imaging to detect and quantify the subtle changes in vocal fold vibrations after superficial dehydration in healthy individuals. Preliminary findings indicate that superficial dehydration in healthy individuals results in spatial deviations at low pitch. However, further studies are warranted to identify additional spatiotemporal changes in vocal fold vibration after superficial dehydration in normal and disordered populations.

Computerized Analysis of Vocal Folds Vibration From Laryngeal Videostroboscopy

OBJECTIVES

To develop an objective analysis of laryngeal videostroboscopy (VSS) movies in the space-time domain for quantitative determination of the true vocal folds (TVFs) vibratory pattern to allow for detection of local pathologies at early stages of development.

METHODS

Contours of the TVF and false vocal folds (FVFs) were tracked on each frame of a VSS movie. A registration algorithm was used with respect to the centerline of the FVF to eliminate movements not related to TVF vibration. The registered contours of the TVF were analyzed in time and frequency domains.

RESULTS

The TVF vibration demonstrated a sinusoidal pattern with the same fundamental frequency at every section along the folds of healthy subjects, as well as detection of an abnormal area with a different fundamental frequency in TVF with local pathologies. Analysis of the TVF vibration time delay of healthy subject revealed a posterior-to-anterior longitudinal wave that was not detected by visual observation.

CONCLUSIONS

An objective analysis of laryngeal VSS movies was developed for quantitative determination of the TVF vibration. This analysis was able to detect and quantify TVF characteristics in normal subjects as well as in patients with pathologies beyond the ability of examinee's naked eyes.

Fully automated glottis segmentation in endoscopic videos using local color and shape features of glottal regions

Exact analysis of glottal vibration patterns is indispensable for the assessment of laryngeal pathologies. Increasing demand of voice related examination and large amount of data provided by high-speed laryngoscopy and stroboscopy call for automatic assistance in research and patient care. Automatic glottis segmentation is necessary to assist glottal vibration pattern analysis, but unfortunately proves to be very challenging. Previous glottis segmentation approaches hardly consider characteristic glottis features as well as inhomogeneity of glottal regions and show serious drawbacks in their application for diagnostic purposes. We developed a fully automated glottis segmentation framework that extracts a set of glottal regions in endoscopic videos by using a flexible thresholding technique combined with a refining level set method that incorporates prior glottis shape knowledge. A novel descriptor for glottal regions is presented to remove potential nonglottal fake regions that show glottis-like shape properties. Knowledge of local color distributions is incorporated into Bayesian probability image generation. Glottal regions are then tracked frame-by-frame in probability images with a region-based level set segmentation strategy. Principal component analysis of pixel coordinates is applied to determine glottal orientation in each frame and to remove nonglottal regions if erroneous regions are included. The framework shows very promising results concerning segmentation accuracy and processing times and is applicable for both stroboscopic and high-speed videos.

The glottaltopogram: a method of analyzing high-speed images of the vocal folds

Laryngeal high-speed videoendoscopy is a state-of-the-art technique to examine physiological vibrational patterns of the vocal folds. With sampling rates of thousands of frames per second, high-speed videoendoscopy produces a large amount of data that is difficult to analyze subjectively. In order to visualize high-speed video in a straightforward and intuitive way, many methods have been proposed to condense the three-dimensional data into a few static images that preserve characteristics of the underlying vocal fold vibratory patterns. In this paper, we propose the "glottaltopogram," which is based on principal component analysis of changes over time in the brightness of each pixel in consecutive video images. This method reveals the overall synchronization of the vibrational patterns of the vocal folds over the entire laryngeal area. Experimental results showed that this method is effective in visualizing pathological and normal vocal fold vibratory patterns.

Spatiotemporal analysis of high-speed videolaryngoscopic imaging of organic pathologies in males

PURPOSE

The aim of this study was to identify parameters that would differentiate healthy from pathological organic-based vocal fold vibrations to emphasize clinical usefulness of high-speed imaging.

METHOD

Fifty-five men (M age = 36 years, SD = 20 years) were examined and separated into 4 groups: 1 healthy (26 individuals) and 3 pathological (10 individuals with contact granuloma, 12 with polyps, and 7 with cysts). Vocal fold vibrations were recorded using a high-speed camera during sustained phonation. Twenty objective glottal area waveform and 24 phonovibrogram parameters representing spatiotemporal characteristics were analyzed. Statistical group comparisons were performed to document spatiotemporal changes for organic lesions that cannot be determined visually. To look for specific pattern profiles within organic lesions, the authors performed linear discriminant analysis.

RESULTS

Thirteen parameters showed significant differences between the healthy group and at least 1 pathological group. The differences occurred more in temporal than in spatial parameters. Contact granuloma showed the fewest statistical differences (3 parameters), followed by cysts (9 parameters), and polyps (10 parameters). Linear discriminant analysis achieved accuracy performance of 76% (all groups separated) and 82% (healthy vs. pathological).

CONCLUSION

The results suggest that for males, the differences between healthy voices and organic voice disorders may be more pronounced within temporal characteristics that cannot be visually detected without high-speed imaging.

Quantitative measurement of vocal fold vibration in male radio performers and healthy controls using high-speed videoendoscopy

PURPOSE

Acoustic and perceptual studies show a number of differences between the voices of radio performers and controls. Despite this, the vocal fold kinematics underlying these differences are largely unknown. Using high-speed videoendoscopy, this study sought to determine whether the vocal vibration features of radio performers differed from those of non-performing controls.

METHOD

Using high-speed videoendoscopy, recordings of a mid-phonatory/i/ in 16 male radio performers (aged 25-52 years) and 16 age-matched controls (aged 25-52 years) were collected. Videos were extracted and analysed semi-automatically using High-Speed Video Program, obtaining measures of fundamental frequency (f0), open quotient and speed quotient. Post-hoc analyses of sound pressure level (SPL) were also performed (n = 19). Pearson's correlations were calculated between SPL and both speed and open quotients.

RESULTS

Male radio performers had a significantly higher speed quotient than their matched controls (t = 3.308, p = 0.005). No significant differences were found for f0 or open quotient. No significant correlation was found between either open or speed quotient with SPL.

DISCUSSION

A higher speed quotient in male radio performers suggests that their vocal fold vibration was characterised by a higher ratio of glottal opening to closing times than controls. This result may explain findings of better voice quality, higher equivalent sound level and greater spectral tilt seen in previous research. Open quotient was not significantly different between groups, indicating that the durations of complete vocal fold closure were not different between the radio performers and controls. Further validation of these results is required to determine the aetiology of the higher speed quotient result and its implications for voice training and clinical management in performers.

Complex vibratory patterns in an elephant larynx

Elephants' low-frequency vocalizations are produced by flow-induced self-sustaining oscillations of laryngeal tissue. To date, little is known in detail about the vibratory phenomena in the elephant larynx. Here, we provide a first descriptive report of the complex oscillatory features found in the excised larynx of a 25 year old female African elephant (Loxodonta africana), the largest animal sound generator ever studied experimentally. Sound production was documented with high-speed video, acoustic measurements, air flow and sound pressure level recordings. The anatomy of the larynx was studied with computed tomography (CT) and dissections. Elephant CT vocal anatomy data were further compared with the anatomy of an adult human male. We observed numerous unusual phenomena, not typically reported in human vocal fold vibrations. Phase delays along both the inferior-superior and anterior-posterior (A-P) dimension were commonly observed, as well as transverse travelling wave patterns along the A-P dimension, previously not documented in the literature. Acoustic energy was mainly created during the instant of glottal opening. The vestibular folds, when adducted, participated in tissue vibration, effectively increasing the generated sound pressure level by 12 dB. The complexity of the observed phenomena is partly attributed to the distinct laryngeal anatomy of the elephant larynx, which is not simply a large-scale version of its human counterpart. Travelling waves may be facilitated by low fundamental frequencies and increased vocal fold tension. A travelling wave model is proposed, to account for three types of phenomena: A-P travelling waves, 'conventional' standing wave patterns, and irregular vocal fold vibration.

Quantifying spatiotemporal properties of vocal fold dynamics based on a multiscale analysis of phonovibrograms

In order to objectively assess the laryngeal vibratory behavior, endoscopic high-speed cameras capture several thousand frames per second of the vocal folds during phonation. However, judging all inherent clinically relevant features is a challenging task and requires well-founded expert knowledge. In this study, an automated wavelet-based analysis of laryngeal high-speed videos based on phonovibrograms is presented. The phonovibrogram is an image representation of the spatiotemporal pattern of vocal fold vibration and constitutes the basis for a computer-based analysis of laryngeal dynamics. The features extracted from the wavelet transform are shown to be closely related to a basic set of video-based measurements categorized by the European Laryngological Society for a subjective assessment of pathologic voices. The wavelet-based analysis further offers information about irregularity and lateral asymmetry and asynchrony. It is demonstrated in healthy and pathologic subjects as well as for a surgical group that was examined before and after the removal of a vocal fold polyp. The features were found to not only classify glottal closure characteristics but also quantify the impact of pathologies on the vibratory behavior. The interpretability and the discriminative power of the proposed feature set show promising relevance for a computer-assisted diagnosis and classification of voice disorders.

Preliminary results on the influence of engineered artificial mucus layer on phonation

PURPOSE Previous studies have confirmed the influence of dehydration and an altered mucus (e.g., due to pathologies) on phonation. However, the underlying reasons for these influences are not fully understood. This study was a preliminary inquiry into the influences of mucus architecture and concentration on vocal fold oscillation. METHOD Two excised human larynges were investigated in an in vitro setup. The oscillations of the vocal folds at various airflow volume rates were recorded through the use of high-speed imaging. Engineered mucus containing polymers (interconnected polymers and linear polymers) was applied to the vocal folds. From the high-speed footage, glottal parameters were extracted through the use of objective methods and were compared to a gold standard (physiological saline solution). RESULTS Variations were found for all applications of mucus. Fundamental frequency dropped and the oscillatory behavior (speed quotient [SQ], closing quotient [CQ]) changed for both larynges. The 2 applied mucus architectures displayed different effects on the larynges. The interconnected polymer displayed clear low-pass filter characteristics not found for the linear polymer. Increase of polymer concentration affected parameters to a certain point. CONCLUSION The data confirm results found in previous studies. Furthermore, the different effects-comparing architecture and concentration-suggest that, in the future, synthetic mucus can be designed to improve phonation.

Characterizing vibratory kinematics in children and adults with high-speed digital imaging

PURPOSE The aim of this study is to quantify and identify characteristic vibratory motion in typically developing prepubertal children and young adults using high-speed digital imaging. METHOD The vibrations of the vocal folds were recorded from 27 children (ages 5-9 years) and 35 adults (ages 21-45 years), with high speed at 4,000 frames per second for sustained phonation. Kinematic features of amplitude periodicity, time periodicity, phase asymmetry, spatial symmetry, and glottal gap index were analyzed from the glottal area waveform across mean and standard deviation (i.e., intercycle variability) for each measure. RESULTS Children exhibited lower mean amplitude periodicity compared to men and women and lower time periodicity compared to men. Children and women exhibited greater variability in amplitude periodicity, time periodicity, phase asymmetry, and glottal gap index compared to men. Women had lower mean values of amplitude periodicity and time periodicity compared to men. CONCLUSION Children differed both spatially but more temporally in vocal fold motion, suggesting the need for the development of children-specific kinematic norms. Results suggest more uncontrolled vibratory motion in children, reflecting changes in the vocal fold layered structure and aero-acoustic source mechanisms.

Glottal opening and closing events investigated by electroglottography and super-high-speed video recordings

Previous research has suggested that the peaks in the first derivative (dEGG) of the electroglottographic (EGG) signal are good approximate indicators of the events of glottal opening and closing. These findings were based on high-speed video (HSV) recordings with frame rates 10 times lower than the sampling frequencies of the corresponding EGG data. The present study attempts to corroborate these previous findings, utilizing super-HSV recordings. The HSV and EGG recordings (sampled at 27 and 44 kHz, respectively) of an excised canine larynx phonation were synchronized by an external TTL signal to within 0.037 ms. Data were analyzed by means of glottovibrograms, digital kymograms, the glottal area waveform and the vocal fold contact length (VFCL), a new parameter representing the time-varying degree of ‘zippering’ closure along the anterior–posterior (A–P) glottal axis. The temporal offsets between glottal events (depicted in the HSV recordings) and dEGG peaks in the opening and closing phase of glottal vibration ranged from 0.02 to 0.61 ms, amounting to 0.24–10.88% of the respective glottal cycle durations. All dEGG double peaks coincided with vibratory A–P phase differences. In two out of the three analyzed video sequences, peaks in the first derivative of the VFCL coincided with dEGG peaks, again co-occurring with A–P phase differences. The findings suggest that dEGG peaks do not always coincide with the events of glottal closure and initial opening. Vocal fold contacting and de-contacting do not occur at infinitesimally small instants of time, but extend over a certain interval, particularly under the influence of A–P phase differences.

Measurement of glottal cycle characteristics between children and adults: physiological variations

OBJECTIVES

The aim of this study was to quantify phases of the vibratory cycle using measurements of glottal cycle quotients and glottal cycle derivatives, in typically developing prepubertal children and young adults with the use of high-speed digital imaging (HSDI).

METHODS

Vocal fold vibrations were recorded from 27 children (age range 5-9 years) and 35 adults (age range 21-45 years), with HSDI at 4000 frames per second for sustained phonation. Glottal area waveform measures of Open Quotient, Closing Quotient, Speed Index (SI), Rate Quotient, and Asymmetry Quotient (AsyQ) were computed. Glottal cycle derivatives of Amplitude Quotient (AQ) and Maximum Area Declination Rate (MADR) were also computed. Group differences (adult females, adult males, and children) were statistically investigated for mean and standard deviation values of the glottal cycle quotients and glottal cycle derivatives.

RESULTS

Children exhibited higher values of SI and AsyQ and lower values of MADR compared with adult males. Children exhibited the highest mean value and lowest variability in AQ compared with adult males and females. Adult males showed lower values of SI, AsyQ, AQ, and higher values of MADR compared with adult females.

CONCLUSIONS

Glottal cycle vibratory motion in children is functionally different compared with adult males and females, suggesting the need for development of children specific norms for both normal and disordered voice qualities.

Non-invasive in vivo measurement of the shear modulus of human vocal fold tissue

Voice is the essential part of singing and speech communication. Voice disorders significantly affect the quality of life. The viscoelastic mechanical properties of the vocal fold mucosa determine the characteristics of the vocal folds oscillations, and thereby voice quality. In the present study, a non-invasive method was developed to determine the shear modulus of human vocal fold tissue in vivo via measurements of the mucosal wave propagation speed during phonation. Images of four human subjects' vocal folds were captured using high speed digital imaging (HSDI) and magnetic resonance imaging (MRI) for different phonation pitches, specifically fundamental frequencies between 110 and 440 Hz. The MRI images were used to obtain the morphometric dimensions of each subject's vocal folds in order to determine the pixel size in the high-speed images. The mucosal wave propagation speed was determined for each subject and at each pitch value using an automated image processing algorithm. The transverse shear modulus of the vocal fold mucosa was then calculated from a surface (Rayleigh) wave propagation dispersion equation using the measured wave speeds. It was found that the mucosal wave propagation speed and therefore the shear modulus of the vocal fold tissue were generally greater at higher pitches. The results were in good agreement with those from other studies obtained via in vitro measurements, thereby supporting the validity of the proposed measurement method. This method offers the potential for in vivo clinical assessments of vocal folds viscoelasticity from HSDI.

A multiscale product approach for an automatic classification of voice disorders from endoscopic high-speed videos

Direct observation of vocal fold vibration is indispensable for a clinical diagnosis of voice disorders. Among current imaging techniques, high-speed videoendoscopy constitutes a state-of-the-art method capturing several thousand frames per second of the vocal folds during phonation. Recently, a method for extracting descriptive features from phonovibrograms, a two-dimensional image containing the spatio-temporal pattern of vocal fold dynamics, was presented. The derived features are closely related to a clinically established protocol for functional assessment of pathologic voices. The discriminative power of these features for different pathologic findings and configurations has not been assessed yet. In the current study, a collective of 220 subjects is considered for two- and multi-class problems of healthy and pathologic findings. The performance of the proposed feature set is compared to conventional feature reduction routines and was found to clearly outperform these. As such, the proposed procedure shows great potential for diagnostical issues of vocal fold disorders.

Measuring body layer vibration of vocal folds by high-frame-rate ultrasound synchronized with a modified electroglottograph

The body-cover concept suggests that the vibration of body layer is an indispensable component of vocal fold vibration. To quantify this vibration, a synchronized system composed of a high-frame-rate ultrasound and a modified electroglottograph (EGG) was employed in this paper to simultaneously image the body layer vibration and record the vocal fold vibration phase information during natural phonations. After data acquisition, the displacements of in vivo body layer vibrations were measured from the ultrasonic radio frequency data, and the temporal reconstruction method was used to enhance the measurement accuracy. Results showed that the modified EGG, the waveform and characteristic points of which were identical to the conventional EGG, resolved the position conflict between the ultrasound transducer and EGG electrodes. The location and range of the vibrating body layer in the estimated displacement image were more clear and discernible than in the ultrasonic B-mode image. Quantitative analysis for vibration features of the body layer demonstrated that the body layer moved as a unit in the superior-inferior direction during the phonation of normal chest registers.

Kymographic imaging of laryngeal vibrations

PURPOSE OF REVIEW

Kymographic imaging is a modern method for displaying and evaluating vibratory behaviour of the vocal folds which is crucial for voice production. This review summarizes the state of the art of this method, and focuses on the progress in this area within the last 5 years.

RECENT FINDINGS

Videokymography, using a special videocamera, offers high-speed (video)kymographic images in real time, which is advantageous in daily clinical practice. Two other methods use software to create kymograms retrospectively: digital kymography processes high-speed videolaryngoscopic recordings and offers numerous research possibilities, whereas strobovideokymography processes videostroboscopic recordings, and its use is limited to regular vibration patterns. Current studies reveal that high-speed kymographic images allow more reliable visual evaluation of vibrations than by watching video recordings. Image analysis procedures have been advanced to quantify the vibration properties of the vocal folds. New information has been obtained on asymmetry, mucosal waves, irregularities, phonation onset, and nonlinear dynamic phenomena in voice disorders, as well as in singing.

SUMMARY

High-speed kymography visualizes vibratory features which are not simply observable via traditional methods. It shows large potential in better understanding the functional origin of hoarseness and unsteady phonatory states. Further research in this area is envisioned.

Quantitative analysis of organic vocal fold pathologies in females by high-speed endoscopy

OBJECTIVES/HYPOTHESIS

Quantitative analysis of endoscopic high-speed video recordings of vocal fold vibrations has been growing in importance in recent years. The videos have mainly been analyzed using subjective evaluation, but this is examiner dependent, and the results show inadequate interobserver agreement. The aims of this study were therefore to identify appropriate objective parameters for analyzing high-speed recordings to differentiate healthy voice production from organic disorders.

STUDY DESIGN

METHODS

A total of 152 females were examined, divided into 77 healthy and 75 with four different pathological conditions: laryngeal epithelial thickening, Reinke edema, vocal fold polyps, and vocal fold cysts. Vocal fold vibrations were recorded with a high-speed camera (4,000 Hz, 256 × 256 pixels) during sustained phonation. Parameters computed from the glottal area waveform (GAW) and from phonovibrogram (PVG) were analyzed. Multiparametric linear discriminant analysis was performed to classify pathological conditions versus the healthy group.

RESULTS

Twenty of 44 parameters were identified that are capable of distinguishing between the individual types of pathology. PVG parameters showed better performance than GAW parameters. Parameters representing vibrational periodicity via standard deviation showed better performance than absolute parameters. In addition, linear discriminant analysis achieved reliable differentiation between healthy and pathological vocal fold vibrations: 72% for the five-class problem (all groups separately) and 88% for the two-class problem (healthy vs. all pathologies taken as one class).

CONCLUSIONS

The study succeeded in defining objective parameters for analyzing endoscopic high-speed videos and suggesting first parameters for differentiation between healthy dynamics and dynamics of organic pathologies.

Phonovibrographic wavegrams: visualizing vocal fold kinematics

Recently, endoscopic high-speed laryngoscopy has been established for commercial use as a state-of-the-art technique to examine vocal fold kinematics. Since modern cameras provide sampling rates of several thousand frames per second, a high volume of data has to be considered for visual and objective analysis. A method for visualizing endoscopic high speed videos in three-dimensional cycle-based graphs combining and extending the approaches of phonovibrograms and electroglottographic wavegrams is presented. To build a phonovibrographic wavegram, individual cycles of a phonovibrogram are segmented, normalized in cycle duration, and concatenated over time. For analyzing purposes, the emerging three-dimensional scalar field is visualized with different rendering techniques providing information of different aspects of vocal fold kinematics. The phonovibrographic wavegram incorporates information about the glottal closure type, size, and location of the amplitudes, symmetry, periodicity, and phase information. The potential of the approach to visualize the characteristics of vocal fold vibration in a compact and intuitive way is demonstrated within two healthy and three pathologic subjects. The phonovibrographic wavegram allows a comprehensive analysis of vocal fold kinematics and reveals information that remains hidden with other visualization techniques.

A wavelet-based approach for a continuous analysis of phonovibrograms

Recently, endoscopic high-speed laryngoscopy has been established for commercial use and constitutes a state-of-the-art technique to examine vocal fold dynamics. Despite overcoming many limitations of commonly applied stroboscopy it has not gained widespread clinical application, yet. A major drawback is a missing methodology of extracting valuable features to support visual assessment or computer-aided diagnosis. In this paper a compact and descriptive feature set is presented. The feature extraction routines are based on two-dimensional color graphs called phonovibrograms (PVG). These graphs contain the full spatio-temporal pattern of vocal fold dynamics and are therefore suited to derive features that comprehensively describe the vibration pattern of vocal folds. Within our approach, clinically relevant features such as glottal closure type, symmetry and periodicity are quantified in a set of 10 descriptive features. The suitability for classification tasks is shown using a clinical data set comprising 50 healthy and 50 paralytic subjects. A classification accuracy of 93.2% has been achieved.

Vocal fold vibration amplitude, open quotient, speed quotient and their variability along glottal length: kymographic data from normal subjects

Abstract Quantitative knowledge about healthy vocal fold vibration characteristics provides the basis for an objective assessment of vocal fold vibrations. In this study, using high-speed videolaryngoscopy the alterations of the relative vibration amplitudes, open quotients, and speed quotients were analyzed along the glottal length in 30 male and 30 female healthy subjects. The maximum vibration amplitude was identified at 41.1% ± 10.8% and 46.5% ± 18.0% of the visible glottal length in females and males, respectively. The average open quotients decreased in females and males from posterior to anterior, while the speed quotients did not change systematically. The reported normative values can be used to distinguish normal and abnormal vibrations in clinical practice when aiming at quantitative diagnosis of functional voice disorders.

How low can you go? Physical production mechanism of elephant infrasonic vocalizations

Elephants can communicate using sounds below the range of human hearing ("infrasounds" below 20 hertz). It is commonly speculated that these vocalizations are produced in the larynx, either by neurally controlled muscle twitching (as in cat purring) or by flow-induced self-sustained vibrations of the vocal folds (as in human speech and song). We used direct high-speed video observations of an excised elephant larynx to demonstrate flow-induced self-sustained vocal fold vibration in the absence of any neural signals, thus excluding the need for any "purring" mechanism. The observed physical principles of voice production apply to a wide variety of mammals, extending across a remarkably large range of fundamental frequencies and body sizes, spanning more than five orders of magnitude.

Spatiotemporal analysis of vocal fold vibrations between children and adults

OBJECTIVES/HYPOTHESIS

Aim of the study is to quantify differences in spatiotemporal features of vibratory motion in typically developing prepubertal children and adults with use of high speed digital imaging.

STUDY DESIGN

Prospective case-control study.

METHODS

Vocal fold oscillations of 31 children and 35 adults were analyzed. Endoscopic high-speed imaging was performed during sustained phonation at typical pitch and loudness. Quantitative technique of Phonovibrogram was used to compute spatiotemporal features. Spatial features are represented by opening and closing angles along the anterior and posterior parts of the vocal folds, as well as by left-right symmetry ratio. Temporal features are represented by the cycle-to-cycle variability of the spatial features. Group differences (adult females, adult males, and children) were statistically investigated.

RESULTS

Statistical differences were more pronounced in the temporal behavior compared to the spatial behavior. Children demonstrated greater cycle-to-cycle variability in oscillations compared to adults. Most differences between children and adults were found for temporal characteristics along the anterior parts during closing phase. The spatiotemporal features differed more between children and males than between children and females. Both adults and children showed equally high left-right symmetry.

CONCLUSIONS

Results suggest a more unstable phonation in children than in adults, yielding increased perturbation in periodicity. Children demonstrated longer phase delay in the anterior/posterior and medio-lateral parts during the opening phase compared to adults. The data presented may provide the bases for differentiating normal vibratory characteristics from the disordered in the pediatric population, and eventually assist in aiding the clinical utility of high speed imaging.

Measuring body-cover vibration of vocal folds based on high frame rate ultrasonic imaging and high-speed video

Vibration of vocal folds is a body-cover layered vibration pattern due to the two-layer tissue structures of vocal folds. A method based on a synchronal imaging system is proposed in order to image and measure the body-cover vibration pattern of vocal folds. This imaging system contains two parts: high-frame-rate ultrasonic imaging part and high-speed video part, which can synchronously image the vibration of the body and cover layers a thigh speed. Then, image analysis methods are applied to measure the body-cover vibration of vocal folds from both recorded image sequences. We analyze characteristics of body-layer vibration based on the measurements from designed experiments. Moreover, these results meet simulations of a body-cover model.

Automated measurement of vocal fold vibratory asymmetry from high-speed videoendoscopy recordings

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.

Objective detection and quantification of mucosal wave propagation

In this work a detection algorithm for mucosal wave propagation is presented. By incorporating physiological knowledge of mucosal wave properties and taking the segmented lateral movement of both vocal fold edges as a basis, the spatio-temporal position of the traveling mucosal wave is identified and quantitatively captured. The course of mucosal wave propagation can be successfully detected and analyzed with regard to discriminating different types of mucosal wave activity (in terms of spread velocity and symmetry). The preliminary results obtained for six exemplary laryngeal high-speed recordings are promising and demonstrate the potential of the proposed detection and objective description approach.

Automatic diagnosis of vocal fold paresis by employing phonovibrogram features and machine learning methods

The clinical diagnosis of voice disorders is based on examination of the rapidly moving vocal folds during phonation (f0: 80-300Hz) with state-of-the-art endoscopic high-speed cameras. Commonly, analysis is performed in a subjective and time-consuming manner via slow-motion video playback and exhibits low inter- and intra-rater reliability. In this study an objective method to overcome this drawback is presented being based on Phonovibrography, a novel image analysis technique. For a collective of 45 normophonic and paralytic voices the laryngeal dynamics were captured by specialized Phonovibrogram features and analyzed with different machine learning algorithms. Classification accuracies reached 93% for 2-class and 73% for 3-class discrimination. The results were validated by subjective expert ratings given the same diagnostic criteria. The automatic Phonovibrogram analysis approach exceeded the experienced raters' classifications by 9%. The presented method holds a lot of potential for providing reliable vocal fold diagnosis support in the future.

Advances in laryngeal imaging

Imaging and image analysis became an important issue in laryngeal diagnostics. Various techniques, such as videostroboscopy, videokymography, digital kymography, or ultrasonography are available and are used in research and clinical practice. This paper reviews recent advances in imaging for laryngeal diagnostics.

[Phonovibrogram: vocal fold dynamics integrated within a single image]

BACKGROUND

Stroboscopy is widely used and is quite adequate for the examination of normal voices, but with increasing hoarseness its suitability declines, even when it is supplemented by video recordings and image evaluation. Real-time procedures such as videokymography or high-speed (HS) video imaging are more suitable methods of observing the movements of the vocal folds in such cases. A drawback of any video recording is the later time-consuming offline replay of the films in slow motion and our restricted pattern recognition for motion and other time-dependent processes.

METHODS

The phonovibrogram (PVG) is an image-processing algorithm that extracts the vocal fold motions of a whole laryngoscopic HS video film and automatically compresses them into a single image.

RESULTS

Simple patterns that vary from person to person are revealed by PVG; these can be categorized by means of simple geometric forms, which a human observer can more easily recognize and interpret than dynamic motion patterns. The PVG computation is described in detail and an extensive guide to interpretation is given, illustrated by reference to theoretical and real examples.

CONCLUSION

In clinical conditions, HS laryngoscopic video recording is useful only in association with automatic image processing. The PVG procedure is a promising approach and tests should be performed with a view to further clinical validation.

Preliminary Study on the Quantitative Analysis of Vocal Loading Effects on Vocal Fold Dynamics Using Phonovibrograms

Objectives:

The purpose of the present study was to determine whether high-speed digital imaging with phonovibrogram (PVG) analysis would identify changes in vocal fold vibratory characteristics following prolonged reading (vocal fatigue) in subjects with normal voice to evaluate the voice effects of vocal loading.

Methods:

Three healthy subjects' larynges were examined with an endoscopic high-speed imaging system at 4 different levels of vocal load. Vocal fold dynamics were segmented and processed by PVGs. The PVG images were quantitatively described by a parameter set enabling an individual characterization of vocal fold dynamics. To reveal differences between the subjects, we performed a linear discrimination analysis. Within each subject, the identification of vocal loading effects was performed by statistical analysis (1-way analysis of variance), and 2-tailed paired t-tests were used as a consistency check between left and right vocal fold sides.

Results:

For each subject, the PVG analysis enabled a precise quantification of the entire range of vocal fold dynamics. Independently of the high-speed videos (vocal loads), each subject could be identified by his or her PVG parameters on linear discrimination analysis. In all subjects, the effect of vocal loading was reflected by alterations of PVG parameters representing the posterior opening and closing dynamics. Evaluation within subjects revealed slight asymmetric vibratory behavior between the left and right vocal folds, confirming earlier assumptions.

Conclusions:

Within the investigated subjects, vocal loading does affect the vibratory characteristics of the vocal folds. Left-right vocal fold vibratory asymmetries do occur in healthy voices and can be identified by PVGs. High-speed digital imaging in combination with PVG analysis seems to be a promising tool for investigation of vocal fold fatigue and disorders resulting even from small dynamic changes.