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Magnetic Resonance Imaging Safety for Patients with Active Hearing Implants

Boek - Dissertatie

The use of medical technologies in both the diagnosis and treatment of several health issues has become common practice. In medical diagnostics, magnetic resonance imaging or MRI has become a widely accepted and preferred imaging technique for many pathologies. This is mainly thanks to the fact that MRI is superior in visualizing soft tissue structures, whilst it does not rely on the use of potentially harmful ionizing radiation. With respect to treating medical conditions, numerous medical devices are being used to alleviate symptoms and improve the quality of life for the patient. The presented work focuses active implantable hearing solutions, which are designed to compensate moderate to severe forms of hearing loss. According to the World Health Organization (WHO), hearing loss is a highly prevalent condition that severely impacts a person's quality of life. Estimates are that by 2050, over 2.5 billion people worldwide will suffer from a certain degree of hearing loss with 700 million of those requiring rehabilitation of some form. Active hearing implants like cochlear or bone conduction implants have been on the market for the past decades, and several hundreds of thousands of people have regained their hearing thanks to these technologies. Mutual interactions between a medical implant and the electromagnetic fields that are present during magnetic resonance (MR) imaging and spectroscopy can cause discomfort or harm to the patient. Several prior reports describing sometimes severe adverse events have led to international efforts towards standardization in order to make MR imaging and spectroscopy in implanted patients safer. Standardization efforts have been focused mainly on passive or active, electrically stimulating implants. The presented work untangles the potential risks for acoustically stimulating hearing implants in the MR environment. The problem is approached holistically, by developing several measurement techniques that allow de-risking MRI-induced risks early in the development process of new devices. First, a literature review is performed together with an analysis of adverse events reported to the American Food and Drug Administration (FDA). This allows to establish both the technical state-of-the-art together with the most common adverse events. As this study illustrates, dislocation of an implanted actuator is a phenomenon that could occur during MRI requiring post-MRI revision surgery. In the second part of this work, a measurement technique is designed that combines a generic test approach with a product-specific technique to quantify the risk of unintended movement for the Cochlear™ Carina® 2 middle ear implant. Unintended movement could be induced due to magnetically induced forces and torques acting upon the implant in the MR environment. Another outcome of the literature review is that unintended acoustic output of implanted actuators is a real risk that can cause discomfort or potentially additional hearing loss upon the patient. In a third part of this work, a generic, optical test framework is developed that allows measuring the microscopic dynamic displacements of these types of actuators in real time during MRI. A case study for the Cochlear™ Carina® 2 middle ear implant shows that the risk of unintended acoustic output during MRI that present audible stimuli is low. The root-mean-square (RMS) pressure in the inner ear - which is believed to be representative for the perceived loudness of sound stimuli - can be measured during MRI as an alternative measurement technique for detecting unintended acoustic output. The potential of this measurement technique is illustrated in a study where the performance of a new active transcutaneous bone conduction implant is investigated in human cadaveric specimen. Finally, it can be seen from the initially performed analysis of literature that manufacturers are working towards safer and easier MRI for their patients. Looking forward, this means that more patients will be allowed in the MR environment and that the diagnostic value of the acquired images becomes more important. Reduction of image artefacts due to the presence of the metallic implants becomes a more important aspect of scanning patients with implants. The fifth part of this work outlines the design of a realistic head phantom, which can be used for artefact reduction studies. The presented work approached the problem of MRI safety for active acoustic hearing implants in a holistic way, providing a strong foundation that will allow safer and easier MRI for patients with active acoustic hearing implants. Further, the techniques developed during this work will enable pre-clinical testing of future generations of these devices which allows de-risking MRI safety earlier in the technology development chain.
Jaar van publicatie:2022
Toegankelijkheid:Open