Otolaryngology - Theses
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ItemImproving the preservation of acoustic hearing for cochlear implant recipients( 2022)Cochlear implants have been widely used to provide an alternative way of hearing for those who have experienced hearing loss, specifically in the high frequencies. Over the years, cochlear implant recipient criteria have expanded to those who are not only classified as severely to profoundly deaf, but also to include those who still have substantial residual hearing, particularly in the low frequencies. The increase in cochlear implant candidacy motivated the development of a new modality for treating patients with residual low-frequency hearing, termed electro-acoustic stimulation. Electro-acoustic stimulation involves electrical stimulation from the implant for mid to high frequencies complementary to low-frequency amplification through hearing aids. The resulting hearing experience has been shown to be advantageous over cochlear implant stimulation alone, allowing for better music appreciation, and improved speech recognition in noise. To achieve electro-acoustic stimulation, the residual low-frequency hearing must be preserved during and following cochlear implantation. Unfortunately, this is not always the case as implantation often results in either immediate or delayed loss of residual hearing loss in the postoperative period in more than half the individuals. Causes for these losses are speculated to be associated with intra-cochlear trauma occurring during electrode array insertion in conjunction with the consequential inflammatory response that ensues. To further improve hearing outcomes in cochlear implantation recipients, the issue currently presented is whether the detection of cochlear injury can be achieved and result in improved hearing preservation rates post-implantation. The investigations in this thesis aim to explore the implementation of a monitoring system, namely impedance, to identify whether an intra-cochlear injury has occurred, such as cochlear wall injury leading to the infiltration of blood into the cochlea. Impedance is a passive electrical measurement that evaluates the resistance and conductivity of the medium surrounding the recording electrodes. Specifically, this thesis will explore relationships between intra-operative impedance measurements and clinical outcomes such as hearing thresholds. Additionally, the impedance will be monitored post-operatively to determine if impedance fluctuations align with physiological events anticipated to occur in the cochlear following implantation that is unfavourable for hearing preservation. Lastly, investigations in this thesis will explore a possible therapeutic intervention for the removal of intra-scalar blood if it were to enter the cochlea during implantation.
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ItemDeep Learning for Three-Dimensional Multi-Modal Medical Image Processing: From Classification to Segmentation( 2022)Deep learning is a state-of-the-art method in machine learning, proven successful in many application domains. This research aims to use a deep learning framework for three-dimensional (3D) medical image segmentation. Multi-modal images are used in this process as they provide additional information that can make segmentation easier. For example, in computed tomography (CT), more rigid materials such as bone are better defined, while in magnetic resonance imaging (MRI), softer materials such as anatomical structures are better defined. However, multi-modal images for the same person may not be in the same orientation and have different resolutions. Therefore, aligning (or registering) multi-modal images prior to segmentation is an important task. Furthermore, the type of image under consideration is essential in the segmentation process. For instance, a method used to segment the brain may not be applicable in segmenting the heart. Therefore, to fully automate the process of segmentation, it is crucial to classify the multi-modal images and register them before performing a segmentation. Thus, in this thesis, we introduce methods based on deep learning for the classification, registration, and segmentation of multi-modal medical images. For each of these tasks, mainly due to practical limitations such as availability of datasets, we develop and validate our methods for one application/dataset. Firstly, we explore the problem of classifying 3D multi-modal images of different organs. To this end, we introduce a rotation and translation invariant classification model. We use the fact that most human organs are (approximately) symmetrical to simplify the problem. We extract a two-dimensional (2D) representative slice of the 3D organs and use that 2D slice as the input to a deep learning model to perform the classification. We prove experimentally that our method is comparable to existing classification techniques when the assumptions of viewing direction and patient orientation are met. Moreover, we establish that it shows high accuracy even when these assumptions are violated, where other methods fail. Secondly, we introduce a novel deep learning method for registering 3D multi-modal medical images of the head. We use image augmentation methods to create synthetic images to supplement an existing dataset. We use a validated method of registration (one plus one evolutionary optimization) to generate ground truth data and use the symmetry of the human head as an initial alignment to aid the optimization process. Before performing the registration, we also use a classification model to identify the imaging modality (MRI and CT) in order to determine the order of input for the registration to make the approach fully automatic. Then, we combine deep and conventional machine learning methods to predict the transformation/registration parameters. We show that the proposed methods outperform similar existing methods on publicly available MRI and CT images of the head. Lastly, we introduce a deep learning framework to perform brain tumor segmentation. To achieve this, we present a method of enhancing an existing MRI dataset by generating synthetic corresponding CT images, where prior domain knowledge of the registration method is applied to get a paired multi-modal ground-truth dataset. We fine-tune our network architecture and training strategies to segment brain tumors and show that the proposed model outperforms similar existing methods.
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ItemExtending the application of virtual reality simulation in temporal bone anatomy and advanced surgical training( 2021)Cochlear implant surgery has a strong foundation in the treatment of profound hearing loss. In the last decade, there have been marked developments in technology which have enabled the expansion of eligibility criteria. Cochlear implantation is now offered to patients with residual low-frequency hearing or those with unilateral or asymmetrical hearing loss. It is evidenced that to optimise hearing outcomes for patients with residual hearing, it is necessary to reduce the trauma during the insertion of the cochlear implant, in particular by precise surgical technique. Current temporal bone surgery training, including cochlear implant surgery, is based on an apprenticeship model, where registrars observe and practice with consultant supervision. Prior to performing surgery on a patient, it is common practice to perform cadaveric temporal bone dissections. In addition to concern regarding decreasing availability of cadaveric temporal bones are financial constraints and regulations that reduce teaching time available in surgery. The generally low caseload, specifically relevant to cochlear implant surgery, minimises the opportunities for apprenticeship training. As such, this traditional model of training is not maintainable. Similar pressures face the training of anatomy of the temporal bone to medical students and junior doctors. While otologic presentations make a sizable proportion of presentations to emergency departments and general practice, due to the reduction in medical school training time, education in otology is in decline. Virtual reality (VR) surgical training is an attractive adjunct to the current training pathway as it provides a cost effective platform where risk-free, repetitive practice is readily available. VR also has several unique benefits. By presenting automated feedback, VR training allows for self-directed learning. In addition, automated assessment tools have been validated to objectively measure performance. While the effectiveness of VR simulation for mastoidectomy training has previously been well established, to the author’s knowledge there have been no VR simulators adapted to teach more complex temporal bone surgery such as cochlear implant surgery, or clinically oriented temporal bone anatomy. The aims of this thesis were: 1) to determine the viability of expanding the role of VR simulation in otology, including anatomy education and advanced temporal bone surgery and 2) to explore patient factors that relate to surgical technique in cochlear implant surgery. To these ends, several investigations were performed. Firstly, a randomised control trial was conducted to determine whether a clinically oriented VR temporal bone simulator module improved anatomy knowledge of medical students and junior doctors. Participants were randomly allocated to three groups of differing display modality: stereoscopic 3D, monoscopic 3D and 2D presentations. The participants completed a pre-tutorial questionnaire before working through the self-guided tutorial. The module was followed by a post-tutorial questionnaire and a retention questionnaire at 6 weeks. The questionnaires assessed factual anatomic knowledge, spatial relationships and clinically oriented knowledge as well as student’s perception of the display modality. It was observed that the module was effective in imparting factual knowledge in all modalities. The students exposed to the 3D technologies performed better in the spatial relationship and clinically oriented questions. The Stereoscopic 3D modality showed particular benefit for ease of use. Secondly, a training module specifically designed for the surgical approach to cochlear implant surgery was assessed with a prospective pre- and post-study of ENT registrars. All participants were exposed to the same training module that included concurrent and terminal feedback on temporal bones with a range of common anatomical variations. The participants’ performances were compared before and after the training. The assessment temporal bones used at the end of training consisted of a mirror image of the one used prior to training and one novel temporal bone. It was found that there was a significant improvement with a large effect size after training for both the previously encountered temporal bone and the novel temporal bone. Thirdly, a conceptual anatomical study was performed using the University of Melbourne temporal bone simulator data. The study explored patient factors that affect the surgical technique used in approaching cochlear implantation. In particular, the relationship of surgical preparation of the facial recess to the acceptable electrode trajectories into the cochlea. It was found that acceptable trajectories through a round window membrane approach most likely originated superiorly in the facial recess, adjacent to the facial nerve. Conversely, acceptable trajectories through a cochleostomy approach most likely originated inferiorly in the facial recess, adjacent to the junction of the facial nerve and chorda tympani. Furthermore, the skeletonisation of the facial recess was found to be critical in the preparation of the temporal bone for a cochleostomy approach. The results presented throughout the thesis will help guide medical educators in the areas of otology and cochlear implant surgery. These results suggest the viability of an expanded application of virtual reality temporal bone simulations to use in anatomy education and advanced temporal bone surgery training.
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ItemImaging the cochlear response to injury( 2019)There are many sites and methods of therapeutic interventions in the ear, but common to most, if not all of them is the risk of degradation of cochlear or vestibular function. This is despite the fact that these interventions are designed particularly to aid function of these organs. The principal aim of this thesis is to explore non-destructive methods of examining the cochlea’s response to attempted therapeutic interventions. Conventional histopathological techniques that have formed the basis of cochlear research over past decades involve potential disruption of anatomical relationships, distortion of fine structures and a lack of a ‘whole cochlear’ picture of the pathological response. Three imaging modalities were selected that were either novel to hearing research or had previously been limited only to descriptive anatomical studies. These imaging techniques were combined with therapeutic interventions that in the clinical setting have the potential to improve or augment hearing. The first experiment of this thesis demonstrated that while continuous drug delivery to the round window membrane may achieve its primary endpoint (BDNF drug effect in the cochlea, in this case), the technique itself involves a risk of cochlear injury which may limit the safety and thus utility of this delivery technique. A combination of destructive and non-destructive imaging techniques was utilised to explore the pathophysiology of this injury. The second experiment investigated the capabilities of heavy-metal augmented MicroCT in assessing the cochlea’s response to implant insertion through characterisation of cochlear endolymphatic hydrops, intrascalar tissue response, changes in vestibular end organ volumes and three-dimensional assessment of implant position. A number of techniques were developed that have been utilised in already published research as well as forming the basis of future study. The third experiment investigated the capability of an emerging imaging technique, TSLIM, to provide more than just anatomical information. With the idea that changes in vascular permeability in the lateral wall of the cochlea may be responsible for changes in scala media observed in Experiment 2, we developed a technique to visualise the permeability of the blood-labyrinthine barrier with spatial resolution sufficient to demonstrate differential vascular permeability in the fibrocyte subregions of the lateral cochlear wall. Furthermore, this technique could be applied to image these changes in the whole cochlea in one instance. The results and techniques presented in this thesis will inform hearing and other researchers of the applicability of these imaging techniques to their research questions to push hearing research beyond histopathology and the mid-modiolar section.
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ItemLocal and systemic steroids in hearing preservation after cochlear implant surgery: are they equivalent?( 2019)Since the conception of the cochlear implant, the criteria for evaluating potential candidates has greatly expanded. We have seen a move to implanting a greater range of ages, including young children, implanting simultaneous bilateral ears, implantation in single sided deafness, and implanting those with a significant level of residual low-frequency hearing. The later permits a combination of electric stimulation from the implant, and natural acoustic stimulation, termed “electroacoustic stimulation”, that greatly enhances an individual’s speech recognition and music appreciation when compared to implant stimulation alone. Unfortunately, implantation often results in either early or delayed loss of residual hearing in the post-operative period. This is speculated to be the result of implantation trauma and delayed inflammatory events. In order for cochlear implantation to progress further, we now find ourselves with the predicament of how to best preserve this hearing. Despite a large body of research into hearing preservation strategies, we are still faced with unacceptable rates of hearing preservation. Corticosteroids are widely used in the peri-operative setting in an attempt to preserve hearing. It is widely believed that that they exert their effects by modulating the inflammatory reaction to an implant. Currently, little is known about the precise mechanism by which corticosteroids preserve hearing after cochlear implantation, or about the optimal administration regimes. The investigations in this thesis aim to explore the mechanism of action of corticosteroids in the context of hearing preservation after cochlear implantation, as well as compare the various routes of administration. Specifically, these investigations will compare local and systemically administered glucocorticoids, pharmacokinetics and pharmacodynamics within the inner ear, and provide a rationale for their administration regimes. Additionally, investigations in this thesis will explore the role of the mineralocorticoid receptor in the pathologic events following cochlear implantation.
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ItemIntraoperative monitoring during cochlear implantation and correlations to preservation of hearing( 2019)Cochlear implants having been widely used over the past few decades to restore or provide hearing to profoundly deaf individuals. Recently the benefit of combining electrical stimulation from a cochlear implant with low frequency natural hearing or acoustically amplified hearing have been recognised. Benefits include better speech understanding in noise and better appreciation of music (Gantz et al., 2005). Unfortunately inserting a cochlear implant presents significant risk to a patient’s natural hearing therefore, although there are great potential benefits, there is also risk. There are numerous causes of hearing loss after cochlear implant surgery (Rowe et al., 2016). One of those causes is physical damage to the fine structures in the cochlear during array insertion. Electrophysiological monitoring is used to maintain the integrity of important structures for many operations such as facial nerve monitoring in many major ear or parotid gland operations and recurrent laryngeal nerve monitoring in thyroid gland surgery. Electrophysiological monitoring of hearing has been used when resecting tumours near the auditory nerve (Cueva, 2012). Monitoring hearing during cochlear implantation seems a logical extension of a surgeon’s arsenal of monitoring tools. This thesis explores the role of intraoperative monitoring of hearing during cochlear implantation with a goal to reduce postoperative hearing loss by avoiding implant related trauma at the time of surgery. This thesis takes a pragmatic approach focussing only on measurement modalities and methodologies which would be feasible to be use in a day-to-day clinical setting. This work involved: 1. Developing a novel electrophysiological recording system leveraging the telemetry capabilities of commercial cochlear implants. 2. A small animal study to technically validate the function of the system. 3. A small human study to validate the practical use of the system and define stimulus parameters and expected response patterns. 4. A larger human study demonstrating the correlation between adverse intraoperative measurements and failure to preserve operative hearing.
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ItemVestibular migraine: a challenging illness to live with and to manage: a qualitative study of patients’ and specialists’ perspectives( 2019)Vestibular migraine (VM) is one of the most common causes of recurrent vertigo with significant effects on patients’ health-related quality of life measures and psychological well-being. It is widely accepted that VM is associated with a range of diagnostic and management challenges for practitioners, predominantly due to the lack of a gold standard diagnostic test and absence of a preferred drug of choice. Consequently, the existing literature is mostly focused on optimising the diagnostics and treatment protocols. Yet, little is known about the therapeutic needs of those who suffer from VM and health professionals’ strategies in providing care beyond medication. This doctoral thesis addresses these gaps in knowledge in two ways: first, by exploring the experiences of vestibular migraineurs in their daily lives and in the management of their condition; second, by juxtaposing these experiences with an exploration of vestibular specialists’ (VSs) perspectives on the management and care of people with VM. This thesis entailed three phases. In Phase A, a preliminary observation of several vestibular migraineurs’ appointments with VSs was conducted to inform the overall direction of the thesis and to fine-tune the research questions. Phase B adopted a qualitative descriptive method across two consecutive studies. In Study 1, 11 adults with VM were interviewed. This study was informed by the preliminary observation in Phase A and explored two aims: 1a) vestibular migraineurs’ lived experiences and therapeutic needs, 1b) vestibular migraineurs’ experiences with healthcare professionals (HCPs). The findings are visually presented in two models: The first model describes participants’ perceptions of living with VM. In this model, VM is depicted as a ‘wall’ to represent participants’ perception of living with extensive functional and psychosocial restrictions. The individual is presented at the centre, surrounded by six aspects of life (i.e., lifestyle, occupation, personal life, self-sufficiency, social network and self-image) and encircled by VM. Hopelessness and isolation are presented adjacent to the VM ‘wall’ to highlight the psychological effects of a restricted life. The second model is a map of vestibular migraineurs’ journeys from symptom presentation to diagnosis/symptom control. This map illustrates the experiences of vestibular migraineurs with different HCPs and represents the convoluted, long and often frustrating journey that patients embark on to find a diagnosis and, possibly, some level of symptom control. This model shows that vestibular migraineurs’ journeys often entail multiple misdiagnoses, dismissals and irrelevant referrals, particularly when patients seek medical advice from general practitioners (GPs). This experience often leads to frustration and loss of trust towards primary care physicians. By contrast, participants depicted a more positive, trusting experience when seeing VSs. Compared to GPs, patients often perceived VSs as more knowledgeable and competent in managing their illness, largely because VSs acknowledged the severity of their illness and did not dismiss them. Vestibular migraineurs’ satisfaction with VSs provided a rationale for exploring these practitioners’ perspectives. The purpose was to elucidate the source of patients’ higher levels of satisfaction and to explore the clinical strategies that VSs adopted in managing VM. Study 2 explored the perspectives of 10 VSs on two topics: 2a) the complexities of VM management and 2b) the features of optimum VM care. VSs were recruited from several fields of balance disorder management including neuro-otology, vestibular audiology, vestibular physiotherapy, and ear, nose and throat surgeons. The outcomes are depicted in two models. The first model illustrates the multidimensionality of complexities posed by VM, indicating that VM is a complex illness to manage due to three factors: 1) scientific ambiguities, 2) patient-related challenges and 3) professional challenges. The second model proposes a framework for VM quality management: ‘SAIPHE’. SAIPHE stands for the six elements that were considered essential for VM quality care: self-efficacy, access, individualisation, wholistic, and education. Each of these elements are described in detail in the thesis. Study 2 concludes Phase B of this thesis. In Phase C, the data obtained in this body of work was triangulated. The outcomes of Study 1 and Study 2 were juxtaposed to examine their consistency. Patients’ accounts of the challenges of living with VM were compared with VSs’ perspectives and elements of SAIPHE were juxtaposed with Study 1 (vestibular migraineurs’ lived experience and expectations of their practitioners). Finally, VSs’ perspectives on features of VM patients’ education/consultation were integrated with vestibular migraineurs’ articulated educational needs and were developed into a VM-specific consultation framework. Overall, the outcomes of this thesis indicate that VM is a complex illness to live with and to manage as its effects extend beyond its immediate symptoms. Patients suffer from functional and psychological implications that, if unattended, could have catastrophic sequelae. Despite advances in evidence-based knowledge, and despite the consistency of VSs’ perspectives, vestibular migraineurs’ needs and expectations are not reflected in non-specialised clinical care, particularly general practice, and frequent misdiagnosis and dismissals create a barrier to timely management of patients’ illnesses. This thesis supports the clinical recommendation of promoting a care plan that extends beyond symptom management and incorporates patient education and management of functional and psychological effects of VM.
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ItemTrauma and residual hearing loss after cochlear implantation surgery( 2019)For the last 30 years, cochlear implantation (CI) surgery has been successfully used for the treatment of severe to profound deafness. With improvements in cochlear implant technology, the surgical criteria have expanded to include patients with residual low frequency hearing. These patients can benefit from simultaneous use of the implant and a hearing aid in the same ear, termed electro-acoustic stimulation (EAS). EAS has been shown to be particularly beneficial for perceptual tasks relying on pitch resolution, such as music appreciation and speech perception in background noise (Gantz et al., 2005, Santa Maria et al., 2013). Unfortunately, residual hearing loss, termed post-implantation hearing loss, occurs in half of all patients, which degrades many of the benefits of EAS (Carlson et al., 2011). Post-implantation hearing loss may arise from direct surgical trauma and indirect damage to the cochlea (Eshraghi and Van de Water, 2006). The causes of direct trauma include surgical access to the cochlea and electrode insertion trauma. This results in several types of tissue injury, which may cause further hearing loss through a biological response, also termed indirect damage. However, the precise contributions of direct and indirect damage to post-implantation hearing loss remain indeterminate, in part, because of the lack of a standardised animal implantation model. Animal experimentations have been partly hampered by the difficult access to the mammalian inner ear and the absence of a consistent implantation technique (Rowe et al., 2016, Smeds et al., 2015, James et al., 2008) that has led to marked differences in the level of trauma and hearing loss (O'Leary et al., 2013, Farhadi et al., 2013, Honeder et al., 2015). The principal aim of this thesis was to examine the different types of cochlear trauma, how they relate to hearing loss and how hearing loss can be prevented. The issues that have been addressed here include cochlear anatomy and imaging techniques, pathology, pharmacology, electrophysiology and force recordings. This thesis begins by establishing a reproducible animal model of cochlear implantation surgery, followed by systematically examination the relevant contributors to surgical trauma and post-implantation hearing loss. From these findings, pharmacological therapy targeting the indirect damage and recording techniques to reduce post-implantation hearing loss have been investigated. An anatomical study of the guinea pig cochlea was initially performed using novel imaging and processing techniques. This study quantitatively described the soft and bony tissue relationships in the complex hook region of the unoperated guinea pig cochlea. A reproducible technique for implanting in an animal was established in this study for the remaining in vivo studies, including the use of a cochleostomy in an anteroinferior plane (highest predictability and smallest risk of trauma) and closer to the round window (lowest force profile). The first in vivo experiment of this thesis investigated the relative influence of implant insertion depth on trauma and hearing loss. This study also explored the use of glucocorticosteroids (‘steroids’) to preserve hearing and target the biological response to the implant. Key findings were that implants deeply inserted or in the presence of an osseous spiral lamina fracture caused the greatest low-frequency hearing loss. Steroids reduced the biological response in the most apical regions but had no effect on hearing thresholds. A second in vivo experiment was performed to further investigate the efficacy of steroids and to explore if trauma and hearing loss could be predicted at the time of surgery through force or electrocochleography recordings. Preserving the compound action potential of the electrocochleography recording was found to be predictive of an atraumatic insertion and reduced post-implantation hearing loss. Conversely, force was correlated with trauma but not hearing loss. Pre-operative steroids were effective in reversing the loss of hearing amplitudes evoked by lower frequency tones during implantation with hard electrodes. The results presented in this thesis will help inform the cochlear implant community of potential techniques to improve hearing preservation surgery. Specifically, these results provide a validated experimental model of hearing preservation surgery. These results also suggest a role for steroids in reducing tissue response and synaptopathy, and for electrocochleography as an intraoperative recording paradigm to reduce trauma and improve post-implantation hearing loss.
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ItemA study of electrical stimulation levels over 10 years for adults using Nucleus cochlear implants( 2017)Cochlear implants have improved sound perception for thousands of people with severe and profound sensorineural hearing loss. To ensure a good quality sound signal, the implant must be individually programmed throughout the user’s lifetime. Programming determines the electrical stimulation level requirements for each electrode of the implant. The frequency with which programming occurs has so far been based primarily on clinical experience and resources available to the clinic for programming purposes. To develop an evidence-based schedule for the frequency of programming, a comprehensive investigation of the change in electrical stimulation level requirements over time for a large group of adults is necessary. The overall purpose of this retrospective study was therefore to investigate the change in electrical stimulation levels up to 10 years postimplantation for a large group of adults using Nucleus cochlear implants. In addition, this study also aimed to investigate whether demographic characteristics and electrode array segments were predictive of the change in electrical stimulation levels. The Cochlear Implant Clinic of the Royal Victorian Eye and Ear Hospital, Victoria, Australia, has been providing programming services for cochlear implant users for over 25 years. The electrical stimulation data obtained at the programming sessions were extracted for 680 participants who used a Nucleus® cochlear implant over the course of 10 years. For each implant user, programming data for the following time points were extracted from Cochlear Limited’s TM Custom Sound 3.2® fitting software: 2, 3, 6, 9 months postimplantation and biennial time points from 1 year up to 10 years postimplantation. For each time point, the mean T level, C level, and dynamic range (DR) were calculated separately for four electrode array segments: apical (mean of electrodes 22, 20, 18), medial (16, 14, and 10) upper-basal (7, 6), and lower-basal (4, 3). The degree of change (DC) in levels between consecutive time points was also calculated. Long-term changes in electrical stimulation levels were also investigated for 128 participants from the same group who had adequate programming data up to 10 years postimplantation. The trends and amount of change in programming levels were investigated separately for the four electrode array segments using regression analyses. The effects of several demographic characteristics (e.g., aetiology and onset of hearing loss) were also investigated. For the 680 participants, the average T levels and C levels were consistent from 3 months and 6 months postimplantation, respectively. In terms of the degree of change between time points, the majority of participants showed an average of ≤ 20% change in levels as a function of DR after the 3- to 6-month time point comparison postimplantation. Long-term patterns of change for 128 individual participants showed that, for 42% of these participants, the electrical stimulation levels remained relatively stable without any significant trends for either the T levels or C levels, from 6 months up to 10 years postimplantation. Some significant changes in levels were evident up to 10 years postimplantation; however, changes were small, equating to less than 6% per year as a function of DR for 75% of the participants and a maximum of 10% change in levels for the remaining 25% of participants. Additional noteworthy findings include the following: 1. For the participants who showed more change in levels in the first 3 to 6 months postimplantation, approximately 70% of these participants showed a non-significant long-term trend in levels up to 10 years postimplantation, 2. The mean T levels and C levels were found to differ significantly for the four electrode array segments in the first 2 years postimplantation, but were relatively consistent in the long-term, and 3. The mean degree of change in levels as a function of DR was significantly greater for the Otosclerosis pathological group (n = 72) compared to all other groups, and for the prelingual onset of deafness group compared to the postlingual group. This thesis provided strong evidence that electrical stimulation levels change in the first 6 months but expected to remain relatively stable up to 10 years postimplantation for the majority of adults using Nucleus cochlear implants. Based on this evidence, a programming protocol for 10 years postimplantation has been proposed. The proposed protocol recommends more frequent programming sessions in the first 6 months compared to the number of sessions thereafter. The reduced number of sessions over an implant user’s lifetime will assist in managing the increasing caseload with the amount of resources currently available for programming. Given that the levels differed across the segments in the first 2 years postimplantation, but not in the long-term, the proposed protocol recommends measuring levels separately for the four segments in the early postimplantation period. This can then be limited to one or two segments beyond 2 years postimplantation. The protocol also suggests that more programming sessions may be required in the first two years for implant users with Otosclerosis and those with a prelingual onset of hearing loss.
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ItemVirtual reality for the training of ear surgery( 2016)In current residency surgical training programs, residents learn by observing their mentor and practicing under his/her supervision. For patient safety, the mentor needs to ensure that residents have sufficient practice before they perform surgery on patients. Simulation, ranging from low fidelity (e.g. suture practice on rubber models) to high fidelity (e.g. cadaveric temporal bone dissection), is ideal for this purpose and cadaveric bone dissection is the gold standard of simulated training for temporal bone surgery. However, it has a few setbacks. For example, it is limited by the shortage of cadaveric temporal bones and the bones have to be discarded after drilling and cannot be reused. Also, it is difficult to ensure that residents are exposed to a wide range of temporal bones, specifically ones with rare anatomical anomalies. Another concern is that illnesses may be transmitted through contact with diseased tissues and fluids. Virtual reality surgical simulation is an alternative form of high fidelity simulation that offers risk-free, relatively low cost training environments that can be used repeatedly if necessary at the convenience of the user. Reviews have found that practicing surgical procedures on virtual reality simulators improves trainees' operative performance. One major factor contributing to the success of virtual reality surgical simulation systems is their ability to capture clinical variation. Current simulators in Ear Nose and Throat (ENT) surgery mostly use the core training methodology: starting from easier procedures and moving onto more difficult ones. However, this configuration has traditionally been based on the same anatomical model. To the author’s best knowledge, there do not exist virtual reality simulators in the field of ENT that capture anatomical variation as a basis for surgical education. The aim of this thesis was to determine whether exposure to anatomical variation in a virtual reality simulated environment leads to better surgical outcomes, to establish the foundations of a more efficient model for surgical education. To achieve this goal, several investigations were carried out. Firstly, a systematic review and meta-analyses were conducted to examine the role of virtual reality simulation based training in ENT surgery, and to investigate whether it can improve the acquisition of surgical skills. This has revealed that there is currently no literature available in this field to inform whether anatomical variation is important for improving outcomes in simulation based surgical training. Secondly, methods were developed to identify internal anatomical structure variation of temporal bones by examining the bony surface landmarks in an effort to guide the selection of specimens that exhibit differences in anatomy. To this end, correlations between internal and external landmarks were determined and mathematical models developed to predict internal structure variation given combinations of multiple external landmarks using a library of CT scans. It was observed that these correlations and mathematical models were able to predict some anatomical variations with a high level of accuracy. Thirdly, to standardize the evaluation of competence in cochleostomy, an objective assessment tool was developed and validated. Its construct validity and inter-rater reliability were established to be high through evaluations of resident and expert performances on a standardized virtual temporal bone conducted by expert assessors using the proposed tool. Lastly, a randomised controlled trial of ENT residents performing cochleostomy was conducted to determine whether anatomical variation in virtual reality simulation based training improved surgical performance. Participants were randomly allocated to two groups: the experimental group who were exposed to a six different temporal bone anatomies over a period of three weeks and the control group who were trained on one standardized temporal bone over the same period of time. At the end of the training period participants’ performance on two novel temporal bones was assessed. It was observed that ENT residents who were exposed to a range of anatomical variations performed significantly better than those trained on a single anatomical model.