An investigation of cochlear dynamics in surgical and implanation processes

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The aim of this research is to improve the understanding of the impact on the cochlear dynamics corresponding to surgical tools, processes and hearing implants such that these can be designed more appropriately in the future. The results suggest that enhanced performance of implants can be achieved by optimisation of the location with respect to the cochlea and have shown that robotic surgical tools used to enable precise, simplified processes can reduce harm and offer other benefits. With an ageing population, and where exposure to noise on daily basis is increased rather than industrial settings, at least two factors of age and noise, will contribute to a greater incidence of hearing loss in the population in the future. In the research a mathematical model of the passive cochlea was produced to increase understanding of the sensitivity and behaviour of the fluid, structure and pressure transients within the cochlea. The investigation has been complemented by an innovative experimental technique developed to evaluate the dynamics in the cochlear fluids while maintaining the integrity of the cochlear structure. This technique builds on the success of the state-of-the-art surgical robotic micro-drill. The micro-drill enables removal of bone tissue to prepare a consistent aperture onto the endosteal membrane within the cochlea. This is known as preparing a ‘Third window’. In this technique the motion of the exposed endosteal membrane is treated as the diaphragm element of a pressure transducer and is measured using a Micro- Scanning Laser Vibrometer operating through a microscope. There are two principal outcomes of the research: First, the approach has enabled disturbances in the cochlea to be contrasted for different surgical techniques, which it is expected to allude preferential methods in future surgery in otology. In particular it was shown that when using the robotic micro-drill to create a cochleostomy that the disturbance amplitude reduces to 1% of that experienced when using conventional drilling. Secondly, an empirically derived frequency map of the cochlea has been produced to understand how the location of implants affects maximum power transmission over the required frequency band. This has also shown the feasibility of exciting the cochlea at a third window in order to amplify cochlear response

Acoustical holography by holographic interferometry

The ability to see with sound has long been an intriguing concept. It is apparent that ultrasonic energy can give an image of an object not obtainable with light or even with x-rays. In this dissertation, a novel three-step acoustical holographic imaging system is described and several means for its implementation are analyzed. A novel holographic acoustic image converter, which constitutes a fundamental link in the three step imaging method was also developed. The use of optical holographic techniques to convert an arbitrary acoustic image to a visible image is conducted and resulted in the introduction of the new technique of Step-biased holographic interferometry , which is shown to permit increasing the sensitivity of conventional holographic interferometry methods by one order of magnitude. A theoretical and experimental study of some possible couplers , for augmenting and amplifying the displacement amplitude of an acoustical diffraction pattern as it is transferred from a surface bounded by water to a surface bounded by air, is conducted. A particularly detailed study is conducted on the two-quarter-wave acoustic impedance transformer, and on a mosaic of step horn velocity amplifiers. The theoretical relations describing the behavior of both the acoustic impedance transformer and the velocity amplifiers are developed and experimentally verified. As a result of using beryllium to construct the first quarter-wave matching plate in the acoustic impedance transformer and the addition of the microhorn structure in the output stage of the image coupler, interelement crosscoupling has been brought down to a minimum value of -25 db, and the coupler sensitivity has been improved. A mechanical advantage (gain) of 40 at 410 KHz across the water air interface with beryllium-epoxy structure has been achieved. As a result of the increased sensitivity of both, the optical system by using the step-biased holographic interferometry, and of the image coupler by using the microhorn velocity amplifiers as well as the partial impedance matching of water to air, a holographic sound image converter having a threshold intensity of 1 mW/cm2 at 410 KHz appears feasible. During the course of this experimentation, useful acoustical and optical methods for tuning and testing the image coupler materials is devised. Finally, the ability of the system to cast real time shadowgrams of the insonified object appears useful for many practical applications requiring real time operation, and by utilizing computer processing, quasi-real time operation can be achieved for the three-dimensional acoustic imaging

Electrophysiologic assessment of (central) auditory processing disorder in children with non-syndromic cleft lip and/or palate

Session 5aPP - Psychological and Physiological Acoustics: Auditory Function, Mechanisms, and Models (Poster Session)Cleft of the lip and/or palate is a common congenital craniofacial malformation worldwide, particularly non-syndromic cleft lip and/or palate (NSCL/P). Though middle ear deficits in this population have been universally noted in numerous studies, other auditory problems including inner ear deficits or cortical dysfunction are rarely reported. A higher prevalence of educational problems has been noted in children with NSCL/P compared to craniofacially normal children. These high level cognitive difficulties cannot be entirely attributed to peripheral hearing loss. Recently it has been suggested that children with NSCLP may be more prone to abnormalities in the auditory cortex. The aim of the present study was to investigate whether school age children with (NSCL/P) have a higher prevalence of indications of (central) auditory processing disorder [(C)APD] compared to normal age matched controls when assessed using auditory event-related potential (ERP) techniques. School children (6 to 15 years) with NSCL/P and normal controls with matched age and gender were recruited. Auditory ERP recordings included auditory brainstem response and late event-related potentials, including the P1-N1-P2 complex and P300 waveforms. Initial findings from the present study are presented and their implications for further research in this area —and clinical intervention—are outlined. © 2012 Acoustical Society of Americapublished_or_final_versio

Localization of the Cochlear Amplifier in Living Sensitive Ears

BACKGROUND: To detect soft sounds, the mammalian cochlea increases its sensitivity by amplifying incoming sounds up to one thousand times. Although the cochlear amplifier is thought to be a local cellular process at an area basal to the response peak on the spiral basilar membrane, its location has not been demonstrated experimentally. METHODOLOGY AND PRINCIPAL FINDINGS: Using a sensitive laser interferometer to measure sub-nanometer vibrations at two locations along the basilar membrane in sensitive gerbil cochleae, here we show that the cochlea can boost soft sound-induced vibrations as much as 50 dB/mm at an area proximal to the response peak on the basilar membrane. The observed amplification works maximally at low sound levels and at frequencies immediately below the peak-response frequency of the measured apical location. The amplification decreases more than 65 dB/mm as sound levels increases. CONCLUSIONS AND SIGNIFICANCE: We conclude that the cochlea amplifier resides at a small longitudinal region basal to the response peak in the sensitive cochlea. These data provides critical information for advancing our knowledge on cochlear mechanisms responsible for the remarkable hearing sensitivity, frequency selectivity and dynamic range

Scanning micro interferometer with tunable diffraction grating for low noise parallel operation

Large area high throughput metrology plays an important role in several technologies like MEMS. In current metrology systems the parallel operation of multiple metrology probes in a tool has been hindered by their bulky sizes. This study approaches this problem by developing a metrology technique based on miniaturized scanning grating interferometers (μSGIs). Miniaturization of the interferometer is realized by novel micromachined tunable gratings fabricated using SOI substrates. These stress free flat gratings show sufficient motion (~500nm), bandwidth (~50 kHz) and low damping ratio (~0.05). Optical setups have been developed for testing the performance of μSGIs and preliminary results show 6.6 μm lateral resolution and sub-angstrom vertical resolution. To achieve high resolution and to reduce the effect of ambient vibrations, the study has developed a novel control algorithm, implemented on FPGA. It has shown significant reduction of vibration noise in 6.5 kHz bandwidth achieving 6x10-5 nmrms/√Hz noise resolution. Modifications of this control scheme enable long range displacement measurements, parallel operation and scanning samples for their dynamic profile. To analyze and simulate similar optical metrology system with active micro-components, separate tools are developed for mechanical, control and optical sub-systems. The results of these programs enable better design optimization for different applications.Ph.D.Committee Chair: Degertekin, Levent; Committee Co-Chair: Kurfess, Thomas; Committee Member: Adibi, Ali; Committee Member: Danyluk, Steven; Committee Member: Hesketh, Pete

A study of the effects of low intensity pulsed ultrasound on bone cells using controlled in vitro exposure methods

Low Intensity Pulsed Ultrasound (LIPUS) is a type of therapeutic ultrasound approved for treatment of non-union fractures since it was found to accelerate healing in a number of in vivo and clinical studies in the 1990’s. However, recent independent clinical trials found no significant healing effects, leading to questions over the effectiveness of the treatment. Many in vitro experiments have not succeeded in finding a clear and consistent mechanism, partly due to the difficulty in designing apparatus to provide adequate control over the LIPUS field applied to cells. This study developed and used controlled in vitro LIPUS exposure methods to investigate the effects of LIPUS fields on bone cells. The field characteristics of LIPUS transducers with operating frequencies of 45 kHz and 1 MHz were investigated by examining manufacturer’s data, measuring the ultrasonic output of a commercial LIPUS transducer and designing and building a new LIPUS transducer based on one of the most common commercial devices. A custom cell culture vessel (the biocell) was developed to allow a cell layer to be grown on a 6 μm-thick membrane and exposed to LIPUS without changing the LIPUS field. The biocell was immersed in a tank of water at a predetermined separation from a LIPUS transducer. Alignment of the transducer and cell layer was controlled via a custom-built positioning system. LIPUS fields experienced by the cell layers were derived from pressure field mapping in a scanning tank, corrected for any transmission loss through the biocell membrane. An acoustic tile placed behind the cell layer minimised reflections. Temperature measurements on the cell growth surface of a biocell mock-up confirmed no significant temperature rise during LIPUS exposures. As the extra-cellular matrix stiffness and topology has a significant effect on cellular responses, a 3D exposure method was also developed by seeding cells on 3D-printed scaffolds. The 3D exposure technique showed promise as a potential method of investigating LIPUS effects on cells in a controlled but more in vivo-like physical environment. The murine preosteoblast cell line MC3T3-E1 was chosen as a suitable bone cell model. Markers were chosen from key studies in the LIPUS literature to assess if the reported cellular responses could be replicated with a controlled exposure system. Cell proliferation was assessed by comparing viable cell counts before and after LIPUS exposure, across the entire growth surface and in pressure bins to assess the effect of pressure amplitude. The expression of protein and genetic markers implicated in mechanotransduction pathways associated with bone growth and mineralisation were also investigated. Initial studies comparing cellular responses to LIPUS at 1 MHz and 45 kHz over a range of pressure amplitudes indicated 45 kHz LIPUS had the least effect on cell counts and PGE2 expression. This led to the hypothesis that the fast rise time of the 1 MHz pressure pulse produced a rapid switch-on of cyclic radiation force, which stimulated cellular mechanotransduction pathways. The fast rise time hypothesis was tested in the Rise Time Study, which compared the effects of exposure to 1 MHz LIPUS with fast and slow rise times. Results of the controlled 2D studies suggested that LIPUS exposure had no significant effect on proliferation and markers associated with mechanotransduction pathways. Effects on mineralisation markers were mixed and likely due to the short-term nature of the study compared with the time period of mineralisation of the MC3T3-E1 cell line. The early mineralisation regulator Runx2 was up-regulated significantly six days post-exposure to fast rise time LIPUS. Runx2 is a key transcription factor whose up-regulation stimulates osteogenic differentiation of Mesenchymal Stem Cells (MSCs) and preosteoblasts, eventually leading to increased mineralisation and hence a healing effect. The result suggests runx2 may be sensitive to ultrasound stimulus alone and, therefore, may be a key marker to explain healing effects of LIPUS. Further study is recommended to repeat and verify the findings

Electrostatic vibration-to-electric energy conversion

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 193-197).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Ultra-Low-Power electronics can perform useful functions with power levels as low as 170 nW. This makes them amenable to powering from ambient sources such as vibration. In this case, they can become autonomous. Motivated by this application, this thesis provides the necessary tools to analyze, design and fabricate MEMS devices capable of electrostatic vibration-to-electric energy conversion at the microwatt level. The fundamental means of en- ergy conversion is a variable capacitor that is excited through a generating energy conversion cycle with every vibration cycle of the converter. This thesis presents a road map on how to design MEMS electrostatic vibration-to- electric energy converters. A proposed converter is designed to illustrate the design process, and is based on vibration levels typical of rotating machinery, which are around 2% of the acceleration of gravity from 1-5 kHz. The converter consists of a square centimeter with a 195 mg proof mass which travels ±200 pm. This mass and travel can couple to a sinusoidal acceleration source of 0.02g at 2.5 kHz, typical of rotating machinery, so as to capture 24 nJ per cycle. This moving proof mass is designed to provide a variable capacitor ranging from 1 pF to 80 pF. Adding a capacitor of 88 pF in parallel with this device will result in a capacitance change from 168 pF to 89 pF that is required to extract 24 nJ using a charge-constrained cycle.(cont.) This device can be attached to power electronics that implement a charge-constrained cycle and deliver 0.5 nJ back to the reservoir for a total power output of 1.3 [mu]/W at 2.5 kHz. The efficiency of the electrical conversion is 2%. Including packaging, the power per volume would be 0.87 [mu]W/cm3 and the power per mass would be 1.3 [mu]W/g. System improvements are also identified such as those that address the principal sources of loss. For example, decreasing the output capacitance of the MOSFET switches from 10 pF to 1 pF, while keeping the energy conversion cycle the same, results in an energy output of 13 nJ out of 24 nJ, for an efficiency of 54% and a power output of 33 [mu]W. This argues strongly for the use of integrated circuits in which the output capacitance of the MOSFET switches can be reduced for this application.José Oscar Mur Miranda.Ph.D