Arne Voie

Multi-electrode cochlear implant and method of manufacturing the same

A multi-electrode cochlear implant is taught in which approximately twenty or more insulated metal wires are wound around a flexible tube. These wires are held in place with a further layer of dielectric insulating material. The insulation is selectively removed with a laser beam to form electrodes. Two or more layers or valences of wires can be used, with the inner layer of wires terminating distal to the outer layers to provide a stepwise approximation of the tapering of the scala tympani. A core of shape memory material may be introduced into the tube, so that the implant will retain an effective shape after implantation.

Three-dimensional reconstruction of the cochlea from two-dimensional images of optical sections

This paper describes a methodology for three-dimensional (3D) computer-aided reconstruction of the guinea pig cochlea using orthogonal-plane fluorescence optical sectioning. Specimens are sectioned optically, allowing them to remain intact during observation. Equations to correct the data for specimen translation and rotation are developed and 3D reconstructions of the scala tympani, round window membrane, and cochlear aqueduct are presented. The error associated with the reconstruction is estimated to be < 19 microns.

Mechanical clot damage from cavitation during sonothrombolysis

Recent studies have shown that high intensity focused ultrasound (HIFU) accelerates thrombolysis for ischemic stroke. Although the mechanisms are not fully understood, cavitation is thought to play an important role. The goal of this paper is to investigate the potential for cavitation to cause mechanical damage to a blood clot. The amount of damage to the fiber network caused by a single bubble expansion and collapse is estimated by two independent approaches: One based on the stretch of individual fibers and the other based on the energy available to break individual fibers. The two methods yield consistent results. The energy method is extended to the more important scenario of a bubble outside a blood clot that collapses asymmetrically creating an impinging jet. This leads to significantly more damage compared to a bubble embedded within the clot structure. Finally, as an example of how one can apply the theory, a simulation of the propagation of HIFU waves through model calvaria of varying density is explored. The maximum amount of energy available to cause damage to a blood clot increases as the density of the calvaria decreases.

Transcranial Near-Infrared Laser Transmission (NILT) Profiles (800 nm): Systematic Comparison in Four Common Research Species.

Background and Purpose Transcranial near-infrared laser therapy (TLT) is a promising and novel method to promote neuroprotection and clinical improvement in both acute and chronic neurodegenerative diseases such as acute ischemic stroke (AIS), traumatic brain injury (TBI), and Alzheimer’s disease (AD) patients based upon efficacy in translational animal models. However, there is limited information in the peer-reviewed literature pertaining to transcranial near-infrared laser transmission (NILT) profiles in various species. Thus, in the present study we systematically evaluated NILT characteristics through the skull of 4 different species: mouse, rat, rabbit and human. Results Using dehydrated skulls from 3 animal species, using a wavelength of 800nm and a surface power density of 700 mW/cm2, NILT decreased from 40.10% (mouse) to 21.24% (rat) to 11.36% (rabbit) as skull thickness measured at bregma increased from 0.44 mm in mouse to 0.83 mm in rat and then 2.11 mm in rabbit. NILT also significantly increased (p<0.05) when animal skulls were hydrated (i.e. compared to dehydrated); but there was no measurable change in thickness due to hydration. In human calvaria, where mean thickness ranged from 7.19 mm at bregma to 5.91 mm in the parietal skull, only 4.18% and 4.24% of applied near-infrared light was transmitted through the skull. There was a slight (9.2-13.4%), but insignificant effect of hydration state on NILT transmission of human skulls, but there was a significant positive correlation between NILT and thickness at bregma and parietal skull, in both hydrated and dehydrated states. Conclusion This is the first systematic study to demonstrate differential NILT through the skulls of 4 different species; with an inverse relationship between NILT and skull thickness. With animal skulls, transmission profiles are dependent upon the hydration state of the skull, with significantly greater penetration through hydrated skulls compared to dehydrated skulls. Using human skulls, we demonstrate a significant correlation between thickness and penetration, but there was no correlation with skull density. The results suggest that TLT should be optimized in animals using novel approaches incorporating human skull characteristics, because of significant variance of NILT profiles directly related to skull thickness.

MR-Guided Focused Ultrasound for Acute Stroke A Rabbit Model

Recent developments in thrombolysis therapy using tissue Plasminogen Activator (tPA) in combination with ultrasound for noninvasive stroke treatment are of great excitement.1–5 The first clinical trials have been successfully initiated, demonstrating the potential benefit of transcranial ultrasound in combination with tPA as an effective vessel recanalizing treatment strategy.6–10 The use of tPA, however, is limited because of its various exclusion criteria, its availability, and its costs. Depending on the literature, the number of patients with stroke receiving tPA treatment ranges between 1.6%11 and 9%,12 averaging 3% to 4% worldwide. Hence, novel treatment options in stroke are in high demand. Neurointerventional methods for mechanical clot retrieval in acute stroke show great potential13–16 but are currently limited to highly specialized centers. Alternative strategies to treat stroke noninvasively and in the absence of tPA might be provided by innovative ultrasound technologies, such as transcranial focused ultrasound (FUS). First investigations in this regard have emphasized the high potential of successful clot lysis in combination with17,18 but, more so, in the absence of tPA.19,20 Very recently, successful transcranial clot lysis within seconds and without the use of tPA has been demonstrated using one of the first transcranial FUS head systems worldwide, designed for therapeutic FUS applications in humans.21 In the following report, the results of recent in vitro studies, first in vivo data using a novel sonothrombolysis model, and a future concept for …

Effects of varying duty cycle and pulse width on high-intensity focused ultrasound (HIFU)-induced transcranial thrombolysis

The goal was to test the effects of various combinations of pulse widths (PW) and duty cycles (DC) on high-intensity focused ultrasound (HIFU)-induced sonothrombolysis efficacy using an in vitro flow model. An ExAblate™ 4000 HIFU headsystem (InSightec, Inc., Israel) was used. Artificial blood clots were placed into test tubes inside a human calvarium and exposed to pulsatile flow. Four different duty cycles were tested against four different pulse widths. For all study groups, an increase in thrombolysis efficacy could be seen in association with increasing DC and/or PW (p < 0.0001). Using transcranial HIFU, significant thrombolysis can be achieved within seconds and without the use of lytic drugs in vitro. Longer duty cycles in combination with longer pulse widths seem to have the highest potential to optimize clot lysis efficacy.

Transcranial sonothrombolysis using high-intensity focused ultrasound: impact of increasing output power on clot fragmentation

BackgroundThe primary goal of this study was to investigate the relationship between increasing output power levels and clot fragmentation during high-intensity focused ultrasound (HIFU)-induced thrombolysis.MethodsA HIFU headsystem, designed for brain applications in humans, was used for this project. A human calvarium was mounted inside the water-filled hemispheric transducer. Artificial thrombi were placed inside the skull and located at the natural focus point of the transducer. Clots were exposed to a range of acoustic output power levels from 0 to 400 W. The other HIFU operating parameters remained constant. To assess clot fragmentation, three filters of different mesh pore sizes were used. To assess sonothrombolysis efficacy, the clot weight loss was measured.ResultsNo evidence of increasing clot fragmentation was found with increasing acoustic intensities in the majority of the study groups of less than 400 W. Increasing clot lysis could be observed with increasing acoustic output powers.ConclusionTranscranial sonothrombolysis could be achieved in vitro within seconds in the absence of tPA and without producing relevant clot fragmentation, using acoustic output powers of <400 W.

Introduction of a Rabbit Carotid Artery Model for Sonothrombolysis Research

The goal of this study was to develop an in vivo sonothrombolysis model for stroke research. The rabbit carotid artery has average vessel diameters similar to human M1/M2 segments and allows generation of a thrombotic occlusion using various kinds of thrombus material as well as thrombus placement under visual control. It further allows real-time monitoring of flow and clot mechanics during the sonothrombolysis procedure using high-frequency diagnostic ultrasound. In the present study, the model will be introduced and first results to show feasibility using diagnostic as well as high-intensity focused ultrasound will be presented.

Parametric mapping and quantitative analysis of the human calvarium.

In this paper we report how thickness and density vary over the calvarium region of a collection of human skulls. Most previous reports involved a limited number of skulls, with a limited number of measurement sites per skull, so data in the literature are sparse. We collected computer tomography (CT) scans of 51 ex vivo human calvaria, and analyzed these in silico using over 2000 measurement sites per skull. Thickness and density were calculated at these sites, for the three skull layers separately and combined, and were mapped parametrically onto the skull surfaces to examine the spatial variations per skull. These were found to be highly variable, and unique descriptors of the individual skulls. Of the three skull layers, the thickness of the inner cortical layer was found to be the most variable, while the least variable was the outer cortical density.

Effects of physical properties of the skull on high intensity focused ultrasound for transcranial sonothrombolysis

The use of high intensity focused ultrasound (HIFU) in transcranial sonothrombolysis is emerging as a promising therapeutic intervention after stroke. Of interest in the present study is the evolution of the wave from transducer to focus, with special attention to two aspects. One is the attenuation of the wave before it reaches the focus, the other is the scattering of the wave at tissue interfaces leading to alteration of the focus. A code developed for tissue ablation (Kohei Okita, Kenji Ono, Shu Takagi, and Yoichiro Matsumoto, Int. J. Numer. Methods Fluids 65:43–66 (2011)), has been modified to study the effect of the physical properties of the skull on the focusing of the HIFU waves. Phase delay of the array transducer is employed to focus the waves. A basic model illustrative of the calvaria of the skull has been used as only the physical properties of the bone are of interest here. Microbubble cavitation has been shown to enhance sonothrombolysis; hence, the altered wave is examined from the point ...