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Biomechanical analysis methods of soft tissue in the larynx

Subject Area Measurement Systems
Medical Physics, Biomedical Technology
Term from 2016 to 2021
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 323404598
 
Final Report Year 2022

Final Report Abstract

Despite the ever growing relevance of the service sector and communication-based professions, our knowledge and understanding of the complex phonation process is only limited. An in-depth analysis of the underlying fluid-structureacoustic-interaction is mandatory. However, the investigation of the vocal folds as oscillation structures largely rely on the evaluation of high-speed recordings of the mucosal surface. There is still a lack of measurement techniques that give scientists and clinicians the ability to measure structural composition and biomechanical characteristics of the vocal folds which influence the phonation process. An in vivo and non-invasive mechanical analysis of the vocal folds would be highly desirable for fundamental research as well as pre-surgical evaluation in the clinical routine. In order to analyze the biomechanical properties of soft tissue inside the larynx, two novel methods have been developed. Both investigate the elasticity of the tissue, but differ in the measurement location and application. The elastography ultrasound is able to determine the static Young’s modulus, the Doppler-laser-vibrometer based dynamic pipette aspiration specifies the dynamic Young’s modulus over a range of 100 Hz to 1000 Hz of the near surface tissue. Both methods were used to examine different laryngeal configurations generated from typical manipulation procedures on the vocal folds (VFs), in order to evaluate the produced changes in the tissue characteristics during full-larynx phonation experiments. Different degrees of adduction of the arythenoid cartilages and variable elongation of the vocal folds by increased load on the thyroid cartilage lead to variable levels of pre-stress in the vocal fold. The influence of these manipulations on different elasticity parameters like the static and dynamic Young’s modulus could be detected and visualized by the developed methods. Furthermore, during hemi-larynx experiments the contact pressure and movement of the VFs have been investigated with a piezo-resistant pressure sensor and specifically developed read-out unit. This unit is able to measure contact pressures with a local resolution of 27.6 Sensel/cm² over a size of 28.5 mm×15.2 mm reaching a frame-rate up to 1200 Hz. In the pending analysis, dynamic parameters of of the dynamic experiments, simultaneous high-speed recordings of the superior vocal fold surface will be correlated with the contact pressures. In summary, the results of this project will allow extensive and unprecedented interpretation of the dynamic phonation process. This will contribute to a comprehensive understanding of the complex interrelations in phonation. It will provide relevant insights for surgical procedures like injection augmentation and tissue engineering for vocal fold implants. Furthermore, the correlation of biomechanical parameters and 2D high-speed parameters will enable the validation of indirect parameters that estimate tissue properties like elasticity and stiffness from velocities and acceleration of the vocal folds in the high-speed recordings. In turn, this will enable a meaningful transfer from ex-vivo results to in-vivo cases in the clinical routine.

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