Graeme Clark Collection
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ItemCochlear view: postoperative radiography for cochlear implantation( 2000)Objective: This study aimed to define a spatial position of the cochlea in the skull based on anatomical studies and to design an appropriate method of skull radiography for demonstration of the multichannel intracochlear electrode array and the structures of the inner ear, for use in evaluating the electrode position and its related pitch perception. Background: The conventional skull radiograph (plain radiograph)can offer a complete and direct image of an intracochlear electrode array, if the x-ray is directed to the cochlea and parallel to the axis of the cochlea. Methods: Measurement from computed tomography imaging and three-dimensional reconstruction were performed to define the spatial position of the cochlea in the skull. Results: A radiographic projection, the cochlear view, was designed. A detailed radiographic method and radiologic interpretation of the cochlear view is described. An improved clinical method for measuring the longitudinal and angular position of the electrodes from the cochlear view is recommended. Conclusions: The application of the cochlear view has proved that it is beneficial postoperatively in documenting the results of cochlear implantation, and in evaluating the depth of insertion and position of individual electrodes. It serves as a valuable reference for managing frequency mapping, optimizing speech processing strategies, and further research purposes. The method can be widely used in cochlear implant clinics because of its simplicity, low radiation, speed, and minimal cost.
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ItemComparison of electrode position in the human cochlea using various perimodiolar electrode arrays( 2000)Objective: This study was conducted to evaluate the insertion properties and intracochlear trajectories of three perimodiolar electrode array designs and to compare these designs with the standard Cochlear /Melbourne array. Background: Advantages to be expected of a perimodiolar electrode array include both a reduction in stimulus thresholds and an increase in dynamic range, resulting in a more localized stimulation pattern of the spiral ganglion cells, reduced power consumption, and, therefore, longer speech processor battery life. Methods: The test arrays were implanted into human temporal bones. Image analysis was performed on a radiograph taken after the insertion. The cochleas were then histologically processed with the electrode array in situ, and the resulting sections were subsequently assessed for position of the electrode array as well as insertion-related intracochlear damage. Results: All perimodiolar electrode arrays were inserted deeper and showed trajectories that were generally closer to the modiolus compared with the standard electrode array. However, although the precurved array designs did not show significant insertion trauma, the method of insertion needed improvement. After insertion of the straight electrode array with positioner, signs of severe insertion trauma in the majority o fimplanted cochleas were found. Conclusions: Although it was possible to position the electrode arrays close to the modiolus, none of the three perimodiolar designs investigated fulfilled satisfactorily all three criteria of being easy, safe, and a traumatic to implant.
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ItemThe role phase-contrast imagining in intra-cochlear electrode development( 2000)In order to improve the design of intracochlear multichannel electrode arrays, it is fundamental that we have knowledge of the exact anatomical , position of the electrode within the scala of the cochlea. Currently, conventional skull radiography is still the mainstay of post-operative radiological assessment of electrode positioning. The present work investigates the use of phase-contrast radiography, a new x-ray modality, to provide improved imaging of the inner ear and the intracochlear electrode array in the human temporal bone (TB).
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ItemSafety studies and preliminary patient trails with a new perimodiolar electrode array( 2000)A new perimodiolar electrode array, the curly-with stylet (CwS), has been developed and undergone safety trials in human cadaver temporal bones. The array was developed as a result of animal and modelling studies which indicated that there are potential advantages in situating the electrode array in closer proximity to the neural elements. Preliminary studies with four patients in Melbourne implanted with a developmental pre-curved array had supported the predictions of lower current requirements and possibly more focussed spread of excitation.
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ItemWhere to now? - Impact of New Technologies on use of cochlear implants( 2000)The history of cochlear implant use by adults and children with profound hearing loss although relatively short (20 some years), has been characterised by continual technological innovations which have enhanced the performance, packaging, and clinical use of these devices. In particular, the development of the Nucleus multiple channel cochlear implant has included a series of speech processing hardware and speech processing strategy, implemented by Cochlear Limited, and based on research findings that have resulted in an increase in mean speech perception benefits for adults and children.
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ItemDevelopment of safe and effective electrodes: a risk management approach [Abstract]( 1999)Results from studies on experimental animals, computer modelling and preliminary psychophysical studies with three patients, have confirmed the potential for subjective improvement with electrode arrays which lie closer to the modiolus than does the Nucleus straight array. Results of psychophysical studies with three cochlear implant patients, using developmental pre-curved arrays, confirm the feasibility of improving patients' performance through improvements in electrode design. In particular, it was found in psychophysical tests, with patients using a developmental pre-curved electrode array, that both maximum comfortable level and threshold reduced with decreasing distance of a stimulated electrode from the modiolus, and that the dynamic range increased. More intense neural excitation patterns were obtained with the closer electrodes. From this it is inferred that the development of more sophisticated electrode arrays, positioned closer to the modiolus than is currently the case with the Nucleus standard array, will enable the development of improved speech processing strategies. There are technical constraints in the design of a peri-modiolar array, and currently a number of approaches to this problem have been investigated. Whilst the goal of the design is that it be effective for sophisticated and variable manners of stimulus delivery, a primary constraint is safety.
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ItemInsertion study using new peri-modiolar electrode array designs [Abstract]( 1999)Intracochlear multi-channel cochlear implants have been shown to successfully provide auditory information for profoundly deaf patients by electrically stimulating discrete populations of auditory nerve fibers via a scala tympani (ST) electrode array. Histological and radiological examination of implanted human temporal bones showed that the current straight Nucleus® array is usually positioned against the outer wall of the ST. An electrode array close to the modiolus could be expected to reduce stimulation thresholds and result in a more localized neural excitation pattern.
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ItemPsychophysics of a peri-modiolar electrode array( 1999)Psychophysical findings in three adult patients implanted with a CI22 cochlear prosthesis (Cochlear Limited) fitted with a developmental peri-modiolar electrode array have been reported. This array was moulded with a curvature approximating that of the inner wall of scala tympani but, after straightening and insertion into the cochlea, it adopted a position on average approximately half way between the inner and outer walls. However, the considerable variations in electrode trajectories across subjects allowed an analysis which could separate the effects due to longitudinal distance into the cochlea and lateral distance from the modiolus. Radiographic analysis enabled the positions of the individual electrodes to be measured, both longitudinally and laterally. This paper presents additional results and an in-depth analysis of the data, supported by psychophysical findings in subjects with straight arrays. It also introduces a model which describes the effect of distance from the modiolus on the loudness growth function.
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ItemBenefits of pre-curved electrode arrays for the Nucleus multichannel cochlear implant [Abstract]( 1998)The purpose of the study was to evaluate whether placement of an electrode closer to the modiolus would provide a more efficient interface with the auditory nerve. A pre-curved, banded 22-electrode array has been developed. Following comprehensive safety studies, the array was inserted in three adult patients. Detailed x-ray analyses have been conducted to specify the positions of the electrode bands. Psychophysical studies have been conducted, within each subject, using electrodes which lie at differing distances from the modiolus. These studies have shown that as the distance from the modiolus decreased, electrode threshold currents decreased and dynamic ranges increased. Thresholds were lower than in a comparison group of standard array users. Forward masking studies showed current spread to be more focused at the electrodes lying closer to the modiolus. Electrode discrimination was also better at electrodes closer to the modiolus. JND for loudness, expressed as a function of dynamic range also decreased in this condition. Thus, a preliminary profile of the parameters of interest, for an improved implant design, suggest that an array which lies closer to the modiolus can result in lower current requirements and a more localised pattern of neural excitation.
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ItemSpatial spread of neural excitation in cochlear implants: comparison of measurements made using NRT and forward masking [Abstract]( 1998)Recently developed technology allows intracochlear potentials to be measured in cochlear implant recipients, using telemetry. Neural response telemetry (NRT) enables the measurement of compound action potentials evoked by stimulation of cochlear implant electrodes. These objective measures can now be compared with related psychophysical measures in humans. We will present data, from both NRT and forward masking, on spatial spread of neural excitation due to stimulation of cochlear implant electrodes. The response fields from more apical neurons will spread quite broadly to the sensing electrodes of an implanted array, resulting in misleadingly broad NRT estimates of the spatial spread of neural excitation. Forward masking, which might itself lay claims to some degree of "objectivity", will not suffer from this limitation. Comparison of data from the two measures will help to determine the limitations of NRT as a tool for measuring spatial spread of neural excitation.