Research Pieter Livens

Abstract

In the first step of the process of hearing, the eardrum captures sound vibrations which are passed on by three ossicles to the fluid-filled cochlea. Computer models play an important role to understand this complicated biomechanical system, but current models still do not allow to visualize how sound energy is transferred from the eardrum to the ossicles, mainly because exact anisotropic material parameter distributions are lacking. Understanding this process is essential to further develop surgical procedures for eardrum reconstruction. In this project, I will perform measurements of 3D eardrum motion to characterize its dynamic properties. Additionally, I will develop a new technique, based on the virtual fields method, to determine the material parameters of the eardrum in situ. These data will deliver important input for the further development of artificial eardrum replacements and will improve material choice in clinical grafting techniques to optimize hearing outcome. I will then use these parameters to build a truly realistic computer model of eardrum mechanics and develop a method to calculate energy flow in curved anisotropic structures such as the eardrum. With this new model and method, I will be able to visualize the flow of sound energy. This will finally answer the fundamental biomechanical question of how the eardrum captures and transfers sound energy, and will lead to an evidence-based tool for optimizing clinical procedures to restore eardrum perforations.

Researcher(s)

• Promoter: Dirckx Joris
• Fellow: Livens Pieter

Research team(s)

• Biophysics and Biomedical Physics
• Biomedical Physics

Project website

Project type(s)

• Research Project

Abstract

The middle ear (ME) contains the eardrum and three small bones, called the ossicles. Together, they enable us to hear sounds by bridging the gap in acoustic impedance between the surrounding air and the fluid-filled inner ear. Hearing loss is an important and growing problem, especially in our aging population. A common problem is calcification of the ME ligaments, called otosclerosis, which reduces the ME's mobility. Otosclerosis is one of the important causes of hearing loss, and it can be surgically treated. Quantitative and evidence-based diagnosis of this pathology will be an important help for the ear-nose-troat (ENT) surgeon, but a good method is still lacking. The location of calcification along the ME chain determines the amount of hearing loss and the type of reconstructive surgery required. State of the art is explorative surgery, in which the surgeon folds away the eardrum and palpates the ME ossicles. Detection of the location of calcification requires a well-trained surgeon and takes valuable time in the operating room. Currently, no evidence-based tool exists to detect the location of otosclerosis along the ME chain accurately. In this project I will turn our new method, called Minimally Invasive Vibrometry (MIVIB), into a tool for clinical diagnosis. MIVIB uses a medically accredited floating mass transducer (FMT, Medel inc., Austria), which is produced as part of an implantable hearing aid, and which is available to us. In our method it is clamped on the first ME ossicle (malleus) and is stimulated using an electrical signal to set the chain of ossicles into vibration without the need of an eardrum. Using a laser vibrometer, the motion of the three ossicles can be measured through the ear canal to objectively quantify their acoustic mobility. This will allow the surgeon to make an evidence-based decision on the location of ossification and appropriate treatment. In our lab we have demonstrated the potential of the method on cadaver temporal bones, but now further research is necessary to prepare the method for clinical use. I will develop a stimulation system with a user-friendly interface, based on prerecorded multisine signals. This stimulation strategy prevents the necessity of synchronization between signal generation and recording. The current cumbersome laboratory A/D system will then be replaced by a simple PC sound interface and a custom developed signal generating device that runs without any additional intervention of the surgeon. Then, in collaboration with University Hospital Oslo, I will test the MIVIB technique in operating room conditions on 3D-printed middle ear samples with fully mobile ossicles. I will use my expertise in finite element modeling to investigate the best placement of the device on the ME chain for diagnostic relevancy. Using the simulations, the best type of clamp to attach the FMT to the ME will be investigated. The BOF grant will allow me to prepare the technique for clinical use, leading to an intensified collaboration with our clinical partners in Oslo and Antwerp University ENT hospitals, where clinical studies will be started after the project. As this new diagnostic tool is unprecedented, an important progress in diagnosis, treatment, and academic output is to be expected.

Researcher(s)

• Promoter: Livens Pieter

Research team(s)

• Biomedical Physics

Project type(s)

• Research Project

Abstract

To efficiently transfer sound from air to the fluid of the inner ear, most species make use of ossicles coupled to an eardrum. Mammals have three ossicles while birds and reptiles only have one ossicle connecting the eardrum directly to the inner ear. Surprisingly they localise and hear sounds as well as similar-sized mammals. An important difference is that roughly half of the terrestrial vertebrates also have an internal connection between both ears. In large animals and in humans, sounds have different travel times and intensities when reaching the ears, and these phase and intensity differences are used to localize sound sources. In small animals such as lizards, the head is too small to deliver significant differences between sounds reaching each ear. I will build on the work of my master thesis to develop accurate computer models for the three main anatomically different lizard-hearing mechanisms. My work will provide the first truly realistic model of the lizard hearing apparatus and it will give an anatomy-based correct model of internally coupled hearing for a broad class of species. To realize this goal, new techniques to determine the material properties of these microstructures will be developed, advanced synchrotron X-ray imaging will be used, and I will push the boundaries of finite-element modelling in highly complicated anatomical structures. My work will reveal the functioning of the lizard ear and the role of the internal connection.

Researcher(s)

• Promoter: Dirckx Joris
• Fellow: Livens Pieter

Research team(s)

• Biophysics and Biomedical Physics

Project type(s)

• Research Project

Abstract

To efficiently transfer sound from air to the fluid of the inner ear, most species make use of ossicles coupled to an eardrum. Mammals have three ossicles while birds and reptiles only have one ossicle connecting the eardrum directly to the inner ear. Surprisingly they localise and hear sounds as well as similar-sized mammals. An important difference is that roughly half of the terrestrial vertebrates also have an internal connection between both ears. In large animals and in humans, sounds have different travel times and intensities when reaching the ears, and these phase and intensity differences are used to localize sound sources. In small animals such as lizards, the head is too small to deliver significant differences between sounds reaching each ear. I will build on the work of my master thesis to develop accurate computer models for the three main anatomically different lizard-hearing mechanisms. My work will provide the first truly realistic model of the lizard hearing apparatus and it will give an anatomy-based correct model of internally coupled hearing for a broad class of species. To realize this goal, new techniques to determine the material properties of these microstructures will be developed, advanced synchrotron X-ray imaging will be used, and I will push the boundaries of finite-element modelling in highly complicated anatomical structures. My work will reveal the functioning of the lizard ear and the role of the internal connection.

Researcher(s)

• Promoter: Dirckx Joris
• Fellow: Livens Pieter

Research team(s)

• Biophysics and Biomedical Physics

Project type(s)

• Research Project