Increased brain coverage and efficiency when measuring current-induced magnetic fields by use of simultaneous multi-slice echo-planar MRI
Teresa Cunha, Fróði Gregersen, Lars G. Hanson, Axel Thielscher
Abstract
Magnetic resonance current density imaging (MRCDI) can non-invasively validate electric field simulations in volume conductor head models. Weak electric currents are injected using scalp electrodes while measuring the MR phase perturbations caused by the tiny magnetic fields (1–2 nT) induced by the current flow in tissue.
Introduction
Stimulation targeting and dose control in transcranial brain stimulation can benefit from electric field simulations in personalized volume conductor models of the head [1]. Invasive measurements in patients and non-human primates have demonstrated reasonable fits between the simulated and measured fields on average.
Materials and methods
Scanning was performed in a 3T MRI scanner (MAGNETOM Prisma, Siemens Healthcare, Erlangen, Germany) using a 64-channel head coil and the “Multi-Band EPI C2P” sequence (https://www.cmrr.umn.edu/multiband/) developed by the Center for Magnetic Resonance Research (CMRR, Minneapolis, Minnesota, USA).
Results
The results of the noise floor measurements are summarized in Fig 2. The noise was quantified as the spatial standard deviation of the current-free images, with SMS acquisitions represented by data points connected by lines, and SS measurements depicted as individual data points (Fig 2A).
Discussion
In this study, we optimized and validated SMS-EPI acquisitions of current-induced magnetic fields for human brain MRCDI. Initial phantom tests without current flow confirmed the expected increase of the noise levels with decreasing interslice gaps and increasing MB factors, which both make the separation of signals from different slices more difficult [22,23].
Conclusions
SMS-EPI provided good measurements of the current-induced magnetic fields that were mostly on par with single-slice results, therefore offering an attractive time-efficient way of increasing brain coverage in MRCDI.
Citation: Cunha T, Gregersen F, Hanson LG, Thielscher A (2026) Increased brain coverage and efficiency when measuring current-induced magnetic fields by use of simultaneous multi-slice echo-planar MRI. PLoS One 21(1): e0341731. https://doi.org/10.1371/journal.pone.0341731
Editor: Ozlem Ipek, King's College London, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
Received: July 1, 2025; Accepted: January 12, 2026; Published: January 23, 2026
Copyright: © 2026 Cunha et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: Data of the human subjects cannot be shared publicly because of privacy restrictions. The phantom data is fully available at OSF (https://doi.org/10.17605/OSF.IO/DCWUN).
Funding: This study was supported by the Lundbeck Foundation (https://lundbeckfonden.com/, grant R313-2019-622 to AT, grant R324-2019-1784 to LGH) and the German Research Foundation (https://www.dfg.de/, DFG grants TH 1330/6-1 and TH 1330/7-1, part of Research Unit FOR 5429 “MeMoSLAP”). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
