Otolaryngology - Theses
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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.
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ItemThe cochlear prosthesis: safety investigations( 1986)The present research used both physiological and histological techniques to assess the effects of chronic intracochlear electrical stimulation on the residual auditory nerve population in cats. Stimuli consisted of charge balanced biphasic current pulses presented at 500 pps. Stimulus levels were in the range 0.5 - 0.9 mA, and 200 us per phase, and developed charge densities of 18 - 32 uC.cm^-2 geom. per phase. These stimulus levels are within the range used clinically. The animals were stimulated for periods of up to 2000 hours during which time electrically evoked auditory brainstem responses (EABRs) were periodically recorded. At the conclusion of the stimulus program spiral ganglion cell survival was assessed for both stimulated and control cochleas; comparison of the two groups showed no statistically significant difference in ganglion cell population. A number of cochleas exhibited various degrees of cochlear pathology in association with a general inflammation reaction. Severe inflammation, observed in four of the 20 cochleas examined, was attributed to the presence of infection and resulted in significant and widespread neural degeneration. The histopathological changes were correlated with changes in the EABR input-output functions and confirmed the physiological viability of these cells. The results of this study indicates that long-term intracochlear electrical stimulation, using carefully controlled biphasic pulses, does not adversely affect the auditory nerve population. However, widespread infection can result in severe loss of auditory nerve fibres and care must be taken in this regard during implant surgery. Finally, the correlation between cochlear histopathology and EABR recordings suggests that the EABR may be a useful physiological tool in determining auditory nerve survival in patients. The impedance of these scala tympani electrodes were monitored throughout the chronic stimulation program and were compared with impedance data from similar electrodes chronically stimulated in inorganic saline. The changes in impedance of the in vivo stimulated electrodes generally correlated with the degree of fibrous tissue reaction adjacent to the electrode surface. These scala tympani electrodes were examined for evidence of corrosion using a scanning electron microscope. The surface of these in vivo electrodes were compared with in vivo control electrodes and in vitro electrodes stimulated in inorganic saline using similar stimulus parameters. The in vitro stimulated electrodes showed evidence of platinum dissolution at high charge densities (36 uC.cm^-2 geom. per phase) and aggregate charge (270 C). Significantly, the in vivo stimulated electrodes showed no evidence of stimulus induced corrosion. Indeed, their surfaces were similar to the in vivo control electrodes. Previous in vitro electrochemical studies have demonstrated that proteins play a significant role in the inhibition of platinum dissolution. The present study has demonstrated an inhibitory effect in vivo which may be due to the presence of proteins. The results from these studies reflect the biocompatible nature of this neural stimulator. Finally, temporary and permanent reductions in the excitability of the auditory nerve were observed following acute stimulation at intensities and rates above the range used clinically. The extent of these changes correlated with the degree of stimulus evoked neural activity. Furthermore, these stimulus induced changes were metabolically active. These findings suggest that the changes in neural excitability were a result of long-term metabolic changes in the stimulated neural population. Moreover they indicate upper functional operating ranges for auditory prostheses using this form of stimulus regime.
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ItemValidation of virtual reality temporal bone simulators in otolaryngology training( 2010)Background: The training of surgeons is a critically important issue for the health care system. While the traditional method of surgical training continues to serve the health care system well, there are many forces both within surgery and in society that are seeking to improve the training of surgeons of the future. Virtual reality simulations have played a major part in the training of the airline industry and the military but its use in otology surgical training has not been fully elucidated. This thesis aims to investigate the role of virtual reality simulation in temporal bone surgical training by testing i) its construct validity, ii) the transferability of skills, iii) to develop an “intelligent” tutor in the virtual reality simulation and iv) to compare self-directed virtual reality simulation training to traditional teaching methods on the performance of cadaver temporal bone dissection. Results: It was found that the University of Melbourne virtual reality temporal bone simulator had construct validity and was able to differentiate not only between experts and novices participants but also intermediate residents. Using it as a teaching tool by a senior otologist it was demonstrated that participants perform better in cadaver temporal bone dissection compared with traditional teaching methods in a randomized control trial. Finally, it was found that the simulator could be used as an “intelligent tutor” independent of expert supervision to teach novice trainees the fundamentals of temporal bone surgery. Once again in a randomized control trial, it was found that training on the VR simulator improved cadaveric temporal bone dissection compared with traditional teaching methods. Conclusion: Virtual reality temporal bone simulators could have a significant role in the education of temporal bone dissection. It’s most significant contribution would be towards novice surgical training by allowing early education to occur on a virtual reality simulator independent of consultant supervision. This would provide a more efficient use of the precious educational resources of cadaver temporal bone as well as time needed from consultant surgeons to teach and supervise junior trainees. While there are queries regarding the fidelity of the virtual reality simulation environment, it is important to remember that appropriate fidelity for the designed task is more important than absolute comparison to reality. In this regard the current virtual reality temporal bone simulator has sufficient realism to teach novice trainees the fundamental basic of temporal bone dissection. Future research direction would focus on determining the transfer of skills and knowledge from the virtual reality simulator to operating room performance as well as broadening the use of the virtual reality simulator to other areas such as technical skills assessment and surgical rehearsal.
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ItemCochlear implant sound coding with across-frequency delays( 2009)The experiments described in this thesis investigate the temporal relationship between frequency bands in a cochlear implant sound processor. Initial studies were of cochlea-based traveling wave delays for cochlear implant sound processing strategies. These were later broadened into studies of an ensemble of across-frequency delays. Before incorporating cochlear delays into a cochlear implant processor, a set of suitable delays was determined with a psychoacoustic calibration to pitch perception, since normal cochlear delays are a function of frequency. The first experiment assessed the perception of pitch evoked by electrical stimuli from cochlear implant electrodes. Six cochlear implant users with acoustic hearing in their non-implanted ears were recruited for this, since they were able to compare electric stimuli to acoustic tones. Traveling wave delays were then computed for each subject using the frequencies matched to their electrodes. These were similar across subjects, ranging over 0-6 milliseconds along the electrode array. The next experiment applied the calibrated delays to the ACE strategy filter outputs before maxima selection. The effects upon speech perception in noise were assessed with cochlear implant users, and a small but significant improvement was observed. A subsequent sensitivity analysis indicated that accurate calibration of the delays might not be necessary after all; instead, a range of across-frequency delays might be similarly beneficial. A computational investigation was performed next, where a corpus of recorded speech was passed through the ACE cochlear implant sound processing strategy in order to determine how across-frequency delays altered the patterns of stimulation. A range of delay vectors were used in combination with a number of processing parameter sets and noise levels. The results showed that additional stimuli from broadband sounds (such as the glottal pulses of vowels) are selected when frequency bands are desynchronized with across-frequency delays. Background noise contains fewer dominant impulses than a single talker and so is not enhanced in this way. In the following experiment, speech perception with an ensemble of across-frequency delays was assessed with eight cochlear implant users. Reverse cochlear delays (high frequency delays) were equivalent to conventional cochlear delays. Benefit was diminished for larger delays. Speech recognition scores were at baseline with random delay assignments. An information transmission analysis of speech in quiet indicated that the discrimination of voiced cues was most improved with across-frequency delays. For some subjects, this was seen as improved vowel discrimination based on formant locations and improved transmission of the place of articulation of consonants. A final study indicated that benefits to speech perception with across-frequency delays are diminished when the number of maxima selected per frame is increased above 8-out-of-22 frequency bands.