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Optical Coherence Tomography for Image-guided Cochlear Implantation

Boek - Dissertatie

According to World Health Organization (WHO), over 5% of the world's population - or 430 million people - require rehabilitation for disabling hearing loss. By 2050, it is expected that nearly 2.5 billion people will be affected by hearing loss, of which at least 700 million will require rehabilitation. Hearing loss has a large impact on professional, social, emotional and cognitive well-being. In the large majority of patients, hearing disability is caused by dysfunction of the hearing receptor cells within the cochlea, which results in impaired understanding of speech - one of the most invalidating manifestations of the hearing loss. Cochlear implants (CIs) have shown a great potential to restore speech understanding in partially and completely deaf patients, which cannot be sufficiently rehabilitated with hearing aids. Since its development in the 1950s, over 736.900 CI devices have been implanted worldwide. A CI translates acoustic signals into electric pulses and directly stimulates the auditory nerve fibers within the cochlea. The implantation of this neuroprosthesis requires surgery, whereby the stimulating electrode is inserted into the cochlea. CI surgery has high rates of success, whereby over 90% of the implanted patients are satisfied with the improved understanding of speech. However, each surgery poses a serious risk for the integrity of the cochlea: up to 32% of electrode insertions cause trauma to the delicate intracochlear structures. Electrode insertion trauma not only compromises the CI performance, but also the residual hearing function in patients with partial hearing loss prior to surgery. Residual hearing loss in turn negatively affects speech understanding in noise and appreciation of music. Studies have shown that the risk of trauma depends on three factors: the individual cochlear anatomy of each patient, the surgical technique and the CI electrode design. However, the exact interplay between these three factors has yet to be fully disentangled. Furthermore, technological advances in surgical techniques and electrode designs were so far unable to prevent insertion trauma and guarantee preservation of residual hearing. In this dissertation, we introduced and validated several techniques, which on the one hand would facilitate the experimental investigation of insertion trauma mechanics and on the other hand have the potential to reduce the risk of trauma in CI surgery. So far, the mechanics of electrode insertion trauma have primarily been studied on human cadaveric cochleae. The human cochlea is embedded in a capsule of thick, cortical bone, prohibiting direct visualization of its internal structures. Therefore, the anatomy and trauma of intracochlear structures is typically investigated by means of histology. Whereas histological analysis enables high-resolution visualization of the intracochlear structures, it is highly destructive and limited to analysis of 2D slices. The first contribution of this dissertation introduced and validated a novel method for contrast-enhanced microCT imaging, which enables nondestructive 3D analysis of fresh-frozen human cochleae, without any need for tissue pre-processing, such as fixation. Whereas human samples are the most representative models of the living cochlea, they have several limitations for fundamental and early translational studies. Firstly, repeated experiments on the same cochlea are not possible, because every electrode insertion can affect the mechanics of future experiments. Secondly, real cochleae cannot be scaled up to test prototypes, which have not yet been miniaturized. Thirdly, the internal structures of the cochlea cannot be visualized without additional costly techniques, such as histology and microCT imaging. Finally, the use of human cadaveric material is strictly regulated and confined to specialized laboratories. In the second contribution of this dissertation we addressed these limitations by developing anatomically, surgically and mechanically representative models of the human cochleae, which can be 3D printed in transparent material at any scale. The cochlear capsule not only makes the insertion trauma more challenging to study, but also contributes to the risk of trauma in CI surgery. As soon as the electrode enters the intracochlear space, the surgeon cannot see the position of the electrode within the cochlea and has to rely on tactile feedback. However, tactile feedback is often unreliable and only provides information once trauma has already occurred. Current preoperative imaging techniques (clinical CT and MRI) and intraoperative monitoring technologies (electrocochleography, x-ray fluoroscopy) also fall short in anticipating the risk of trauma due to their limited resolution. In this dissertation we explored the possibility of using optical coherence tomography (OCT) imaging for intraoperative guidance in CI surgery. This technology enables imaging of biological tissues at a micrometer scale and has already proven to be safe in many other fields of clinical medicine, amongst which ophthalmology, dermatology and interventional cardiology. In the third contribution, we investigated the feasibility of OCT-guided optimal insertion trajectory prediction in CI surgery. Finally, in the fourth contribution we demonstrated that electrode insertion devices can be enhanced with highly-miniaturized optical fibers, to enable real-time monitoring of the electrode position with respect to the cochlear walls during the insertion. This way, the CI surgeon can adjust the insertion trajectory, if deemed necessary to avoid collision with cochlear walls, based on the OCT feedback. Together, these contributions will deepen our understanding of electrode insertion trauma and enable prevention of this complication in future CI surgery, significantly improving its safety and efficacy.
Jaar van publicatie:2022
Toegankelijkheid:Closed