Prediction of peripheral nerve stimulation thresholds of MRI gradient coils using coupled electromagnetic and neurodynamic simulations
Corresponding Author
Mathias Davids
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Heidelberg, BW, Germany
Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts
Correspondence
Mathias Davids, Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, D-68167 Mannheim, Germany. Email: [email protected]
Search for more papers by this authorBastien Guérin
Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts
Harvard Medical School, Boston, Massachusetts
Search for more papers by this authorLothar R. Schad
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Heidelberg, BW, Germany
Search for more papers by this authorLawrence L. Wald
Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts
Harvard Medical School, Boston, Massachusetts
Harvard-MIT Division of Health Sciences Technology, Cambridge, Massachusetts
Search for more papers by this authorCorresponding Author
Mathias Davids
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Heidelberg, BW, Germany
Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts
Correspondence
Mathias Davids, Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, D-68167 Mannheim, Germany. Email: [email protected]
Search for more papers by this authorBastien Guérin
Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts
Harvard Medical School, Boston, Massachusetts
Search for more papers by this authorLothar R. Schad
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Heidelberg, BW, Germany
Search for more papers by this authorLawrence L. Wald
Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts
Harvard Medical School, Boston, Massachusetts
Harvard-MIT Division of Health Sciences Technology, Cambridge, Massachusetts
Search for more papers by this authorFunding information: National Institute of Biomedical Imaging and Bioengineering; National Institute for Mental Health of the National Institutes of Health, Grant/award numbers: R24MH106053, R00EB019482, U01EB025121, and U01EB025162
Abstract
Purpose
As gradient performance increases, peripheral nerve stimulation (PNS) is becoming a significant constraint for fast MRI. Despite its impact, PNS is not directly included in the coil design process. Instead, the PNS characteristics of a gradient are assessed on healthy subjects after prototype construction. We attempt to develop a tool to inform coil design by predicting the PNS thresholds and activation locations in the human body using electromagnetic field simulations coupled to a neurodynamic model. We validate the approach by comparing simulated and experimentally determined thresholds for 3 gradient coils.
Methods
We first compute the electric field induced by the switching fields within a detailed electromagnetic body model, which includes a detailed atlas of peripheral nerves. We then calculate potential changes along the nerves and evaluate their response using a neurodynamic model. Both a male and female body model are used to study 2 body gradients and 1 head gradient.
Results
There was good agreement between the average simulated thresholds of the male and female models with the experimental average (normalized root-mean-square error: <10% and <5% in most cases). The simulation could also interrogate thresholds above those accessible by the experimental setup and allowed identification of the site of stimulation.
Conclusions
Our simulation framework allows accurate prediction of gradient coil PNS thresholds and provides detailed information on location and “next nerve” thresholds that are not available experimentally. As such, we hope that PNS simulations can have a potential role in the design phase of high performance MRI gradient coils.
Supporting Information
Additional Supporting Information may be found in the online version of this article.
| Filename | Description |
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| mrm27382-sup-0001-FigS1-S4.docxWord document, 13.5 MB |
FIGURE S1 Magnetic fields produced by the 3 gradient coils (top to bottom: BG1, BG2, HG1) in central coronal and sagittal planes, scaled to a gradient strength of 10 mT/m. The color bar for the body gradients BG1 and BG2 is scaled differently (max: 4.0 mT), than for the head gradient, HG1 (max: 2.0 mT). Note that in this plot of the magnetic field, the simple linear “gradient” is not visible because of the concomitant magnetic fields (the linear gradient is only visible in a plot of the Bz field component) FIGURE S2 electric field maps (maximum intensity projection) induced by the BG2 coil in the female (top) and the male body model (bottom), scaled to a slew rate of 100 T/m/s. For better visibility, the electric fields in bone are set to zero (the electric field in the bones is usually very high and would dominate the color scale otherwise) FIGURE S3 Maxima of the neural activation function (i.e., second derivative of the electric field projected onto the nerve tracks) induced by the BG2 coil in the female (top) and male (bottom) body models at slew rate of 100 T/m/s. Only the 10% greatest activation function values are shown for clarity FIGURE S4 Simulated PNS threshold curves for BG1 and BG2 (x and z axes) and for HG1 (y and z axes) in terms of the minimum gradient magnitude as a function of the pulse duration for trapezoidal current waveforms. For these gradient axes, the experimental setup did not achieve significant stimulation (i.e., no experimental data is shown). The shaded grey region is the experimentally accessible region |
Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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