Characterization of radio-frequency induced heating near metallic devices in MRI

Abstract: Neuroprosthetics are therapeutic devices that interface directly with the centralnervous system; they can supervise and stimulate both the brain and peripheralnervous tissue, improving the quality of life of individuals suffering from a widevariety of pathologies: these electrical implants can restore lost or damagedsensory and motor function, for example, by providing hearing to the deaf oreliminating debilitating tremors in Parkinson’s patients. With ongoing technicaladvances, implants are becoming increasingly prevalent, allowing for a greaternumber of measurement and stimulation channels.RF-induced heating represents a significant hazard that prevents patients withneuroprosthetics from accessing the vital imaging modality of MRI. WhetherMRI is needed for implantation, post-operative supervision or independentlyof the implant, it is crucial to mitigate the risks to provide patients with accessto MRI. While simpler implants are well-understood, the safety and efficacyof more complex, multi-channel devices remains incompletely characterized.This thesis is dedicated to deepening the understanding of RF-induced heatingnear metallic implants, with a particular emphasis on multi-channel devices.Additionally, it seeks to develop new tools to aid in the investigation of thesedevices, ultimately facilitating the design of safer neuroprosthetics in MRI.To investigate the response of implants to an incident field during an MRIexam, the transfer function approach has been extended to cascaded mediasituations, which are common for neuroprostheics. Standard temperature mea-surements based on point sensors were supplemented by temperature mappingover large areas using the MRI to determine temperature changes. The scatteredelectric field at the interfaces of the implant prototypes with nerve tissue wasmeasured with an electro-optic sensor. Five implant prototypes were manufac-tured, each with an increasing number of channels, which were then subjectedto laboratory measurements and testing the in MR environment.While substantial heating of up to 19.1 K has been measured for the smallestgrids, a trend emerged where the RF induced heating and the scattered electricfields decrease by at least 84% for the largest electrode grid. This reduction canbe found for different immersions where the implant is partially inside a tissuesimulating medium and the distal end is in air. MR thermometry provided 2Dtemperature maps, allowing for the characterization of all contact sites in onemeasurement

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2023

Klassifikation und Themen

• Schlagwort: Kernspintomografie

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2023
• Urheber: Lottner, Thomas
• Beteiligte Personen und Organisationen: Bock, Michael ; Bock, Michael ; Waldmann, Oliver ; Albert-Ludwigs-Universität Freiburg. Medizinische Fakultät ; Klinik für Radiologie. Medizin Physik, Freiburg im Breisgau ; Albert-Ludwigs-Universität Freiburg. Fakultät für Mathematik und Physik

Weitere Informationen

• DOI: 10.6094/UNIFR/238767
• URN: urn:nbn:de:bsz:25-freidok-2387671
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:52 MEZ