Biomechanical analysis methods of soft tissue in the larynx

Voice is probably our most important means of communication. The treatment of voice disorders, therefore, is of high social and economic interest and relevance. New innovative medical strategies are needed to enable early diagnosis especially for cancer and eventually treat and rehabilitate people (patients) concerned. Today, diagnosis is often based on biopsies, where tissue samples from the larynx (voice box) are taken and analyzed in the lab. Due to the small size of the voice producing vocal folds, this is a risky task which is only conducted when inevitable. Early diagnosis or screening, as e.g. performed for breast cancer screening, is today not possible for the larynx. In our study, we suggest new methods allowing for laryngeal tissue analysis, enabling quantitative evaluation of tissue characteristics without injuring the tissue. These methods will yield important early diagnosis in tissue changes as seen in maligne (cancer) or benigne (polyps, cysts) tissue alterations. The project is based upon three hypotheses: 1. Mechanical material parameters of vocal folds can be determined by high frequency ultrasound examination. 2. High frequency ultrasound as well as special laser based elasticity measurement setups are feasible and applicable for clinical in vivo measurements of vocal folds. For those kinds of measurements, the patient must be narcotized. 3. High frequency ultrasound using a stereo ultrasound technique is feasible and applicable for non-invasive visualizing of vocal fold vibrations. Our project deals with the design, implementation and evaluation of laboratory and clinical experiments for the analysis of vocal fold tissue characteristics. Measurement setups will be designed which allow for investigating at first in vitro cadaver larynges and in future in vivo human measurements during clinical examination. This will result in enabling biopsy free tissue analyses. The focus lies on innovative optical, laser based measurement setups for the analysis of biomechanical properties of soft tissue. The outcome of our approach will be an endoscopic method for biomechanical analysis of the focal fold. Supplementary to experiments with artificial tissue material, 50 experiments with cadaver larynges will be performed and statistically analyzed. Furthermore, we will open the field of laryngeal diagnosis for the otherwise well-established medical ultrasound. This will result in noninvasive ultrasonic vocal fold imaging. Assisted by medical doctors, we will show the feasibility and applicability of the new techniques for future clinical in vivo measurements.

Voice is probably the most important means of communication for us humans. Therefore, an impairment or even loss of the voice affects our lives dramatically. Phoniatrics deals with human vocalization, to understand the physiological processes and to develop methods to provide the vocal system with the best possible care in the event of illness or injury. The primary acoustic signal of voice is generated in the larynx, more specifically by the vocal folds, which are excited to vibrate by a flow of air. Accurate knowledge of the properties and changes in these vocal folds is therefore important to understand and influence the process of vocalization. The project therefore dealt with the design, implementation and evaluation of laboratory experiments and clinical measurement technology for the analysis of the mechanical properties of vocal cord tissue. Measurement methods have been developed that initially allow the in vitro examination of cadaveric larynxes and will in future allow the in vivo characterization of human larynxes during medical treatment. Our long-term central question was to what extent optical and ultrasound measurement technology enable an improvement in early laryngeal diagnosis. We therefore answered the following four key questions during the application period: 1. In what way can optical measurement methods contribute to obtaining mechanical material data of the vocal folds? 2. How can ultrasound measurements complement voice diagnosis and therapy? 3. Can vocal cord movement be visualized using stereoscopic ultrasound? 4. What is the most promising method for endoscopic diagnosis of vocal cord tissue for future clinical applications? We defined the following three main goals: 1. The development of laser-assisted measurement technology for the mechanical characterization and the demonstration of miniaturization possibilities. 2. Development of ultrasound-based elastography for the analysis of vocal folds. 3. Demonstrating the potential for clinical application. The project was based on three hypotheses: 1. Mechanical material data of vocal folds can be determined using elastography based on high-frequency ultrasound. 2. High-frequency ultrasound and laser vibrometer-based elasticity measurement, such as pipette aspiration, are applicable for in vivo clinical measurements on vocal folds. 3. Stereoscopic ultrasound is applicable for non-invasive imaging of vocal fold movements. In this project we have succeeded in developing biopsy-free methods for the characterization of vocal folds. The research on laser-based and ultrasound-based methods has provided the most promising results. The non-invasive visualization of vocal fold vibrations by extracorporeal ultrasound, on the other hand, has not proven to be effective. It has been shown that endoscopic methods are superior. Furthermore, preliminary investigations were carried out into the application of optical coherence tomography, a promising laser-based method that could replace classic pipette aspiration. These principles of tissue analysis are not limited to the larynx, but can be applied to other internal organs.