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In the second half of the 20th century, the medical community experienced a major paradigm shift from conventional ‘open’ surgery to Minimally Invasive Procedures (MIP). The philosophy behind MIP is based on the tenet that minimizing the pain and discomfort of the patient is as important as achieving the desired diagnostic or therapeutic result. To achieve this, MIP use small incisions or the body’s natural orifices in order to access the internal organ or tissue of interest resulting in smaller scars, less post-operative pain and shorter revalidation times than would be the case with conventional ’open’ procedures. The obvious drawback of MIP is that direct visualization of the tissue or organ of interest during the procedure is no longer possible and that navigation to and from the site of interest is much more challenging from a technological and dexterity point of view. As a result, in all but a few cases, MIP require thin flexible sensors and/or visualization instruments, called endoscopes. The inherent properties of optical fibers (a very small outer diameter, flexibility, insensitivity to electromagnetic interference and biocompatibility) make fiber optics in combination with micro-optic components an ideal base on which to build sensors and visualization instruments for MIP. In his PhD thesis, Stefaan looked at two different domains in Minimally Invasive Procedures, cochlear implants and endomicroscopy, and researched for each domain how novel fiber optic techniques can help overcome some of the major challenges associated with each.
The cochlea is a fluid filled spiral shaped cavity responsible for electromechanical transduction i.e. the conversion of sound to auditory nerve stimuli. In most cases, hearing loss is caused by problems within the cochlea (sensorineural hearing loss). In some cases of profound sensorineural hearing loss (> 90dB), the use of a cochlear implant can partially restore a sense of hearing to the recipient. A cochlear implant bypasses the cochlea by electrically stimulating the auditory nerve at different positions through an array of electrodes encased in a silicone housing. Correct insertion of the electrode array is of crucial importance since the position of the electrode array will determine the quality of the speech understanding of the patient. Moreover, it is important to avoid causing trauma to the cochlea to preserve the residual hearing. Today, the insertion is mostly done ‘blind’: once the electrode array enters the inside of the cochlea no visual feedback is possible which makes the success of the procedure solely dependent on the dexterity and experience of the surgeon. In the first part of this PhD, Stefaan researched the compatibility of several fiber optic sensing techniques with the cochlear implant insertion procedure given the very stringent constraints and he analyzed how these techniques can help improve the insertion of the electrode array. The second topic of his PhD concerns the miniaturization of flexible fiber optic endoscopes towards diameters smaller than 0.5 mm. Advances in fiber optics and CCD technology in the last decades have allowed for a large reduction in outer diameter (from centimeters to submillimeter) of endoscopes. Attempts to reduce the outer diameter even further, however, have been hindered by the trade-off, inherent to conventional endoscopes, between outer diameter, resolution and field of view. Several groups have shown the feasibility of further miniaturization towards so called micro-endoscopes, albeit at the cost of a very reduced field of view. Stefaan presented the results of his work on the modeling, design and fabrication of an ultra-high NA Coherent Fiber Bundle (CFB) that, in combination with proximal wave front shaping, could be used to circumvent the aforementioned trade-off thus paving the way for even smaller endoscopes.