High speed imaging and measurement of laryngeal vibration during phonation using ultrafast ultrasonography: A preliminary study

Observation and measurement of laryngeal vibration during phonation is essential for study of voice production. Due to the advantages in noninvasiveness and penetration, conventional B mode ultrasonography has been introduced in our previous studies of laryngeal tissue vibration. However, its main drawbacks are the insufficient frame rate, drastically narrowed field of view(FOV) and line to line acquisition lag. Thus, ultrafast ultrasonography that offers a much wider FOV and ultrahigh frame rate is introduced in the present study for observation and measurement of laryngeal vibration. Ultrafast ultrasonography is achieved by emitting a plane wave using the full aperture of a linear array transducer on a scanner(SonixTouch, Ultrasonix, Canada) and then applying beamforming on received raw RF data. The FOV covers the whole glottis as well as sub- and supraglottal structures of the larynx. Non-stationary laryngeal vibration are recorded at 5000 fps when subjects start voicing vowel /u:/ during experiments. To measure the vibration, a RF speckle tracking algorithm based on normalized cross correlation is used. The cross correlation coefficient between the displaced and best matched reference speckle is also obtained at each point within the region of interest. The electroglottogram(EGG) is recorded as a reference indicator of vibration phase. The vibration of the vocal fold can be easily identified and shows clear correlation with EGG waveform. The non-stationary process of the vibration of sub and supra glottal tissue during onset of voicing is well quantified with high temporal resolution, while the vibration of the body and cover of the vocal fold appears chaotic and against mechanical principle. Measurement of vibration of the vocal fold body is compromised by its low signal-to-noise ratio. Measurement of vibration of the vocal fold edge is compromised by severe signal decorrelation. Nevertheless, ultrafast ultrasonography still can be used in visualization and measurement of the vibration and deformation of certain structures in the larynx. Thus, there is potential value of this technique being used in estimation of mechanical properties of laryngeal tissue.