Safety in simultaneous ultra-low-field MRI and MEG: forces exerted on magnetizable objects by magnetic fields

Abstract

Event Abstract Back to Event Safety in simultaneous ultra-low-field MRI and MEG: forces exerted on magnetizable objects by magnetic fields Juhani Dabek1*, Fredrik Sannholm1, Jaakko O. Nieminen1, Panu T. Vesanen1 and Risto J. Ilmoniemi1 1 Aalto University , Finland Magnetic resonance imaging (MRI) can be combined with magnetoencephalography (MEG) in one apparatus (MEG-MRI) to image the human brain. With the current sensor technology, to record the weak biomagnetic signals in MEG-MRI, the MRI sequences are carried out in ultra-low fields, typically in the microtesla regime. On the other hand, in order to guarantee sufficient MR image quality, the sample is prepolarized in a higher magnetic field. Ultra-low-field MRI is generally safe, but, the prepolarization field, although much weaker than the main field in high-field MRI, must be considered for safe operation of the apparatus. It can be shown that for a non-saturated, linearly magnetizable object, the magnetic force on it is directly proportional to the product of the strength of the magnetic field and that of its gradient. On the other hand, the phenomenon of demagnetization causes the force to be weaker on flat objects compared to elongated objects. This has been confirmed by our experiments on the symmetry axis of a Helmholtz coil. These effects need to be considered when the subject to be imaged has, e.g., medical implants or surgical clips. Other prominent risks associated with MRI experiments relate to rapidly switched magnetic fields or their gradients (peripheral nerve stimulation), the possible use of RF pulses (specific absorption rate) and cryogenics (sudden quench). The risks with the magnetic forces on magnetizable objects could result in projectile danger or tissue damage, and need careful study. Important aspects with respect to the potentially affected objects are, e.g., their composition, shape and electrical properties. Eventually, it is proposed that families of metallic objects close to the MEG-MRI apparatus, external or internal to the subject, should be validated for safety with respect to the magnetic forces due to the prepolarization field. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Instrumentation and Multi-modal Integrations: MEG, Low-field MRI,EEG, fMRI,TMS,NIRS Citation: Dabek J, Sannholm F, Nieminen JO, Vesanen PT and Ilmoniemi RJ (2010). Safety in simultaneous ultra-low-field MRI and MEG: forces exerted on magnetizable objects by magnetic fields. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00029 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Mar 2010; Published Online: 19 Mar 2010. * Correspondence: Juhani Dabek, Aalto University, Espoo, Finland, juhani.dabek@tkk.fi Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Juhani Dabek Fredrik Sannholm Jaakko O Nieminen Panu T Vesanen Risto J Ilmoniemi Google Juhani Dabek Fredrik Sannholm Jaakko O Nieminen Panu T Vesanen Risto J Ilmoniemi Google Scholar Juhani Dabek Fredrik Sannholm Jaakko O Nieminen Panu T Vesanen Risto J Ilmoniemi PubMed Juhani Dabek Fredrik Sannholm Jaakko O Nieminen Panu T Vesanen Risto J Ilmoniemi Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.