Peripheral nerve stimulation limits of a high amplitude and slew rate magnetic field gradient coil for neuroimaging

Purpose To establish peripheral nerve stimulation (PNS) thresholds for an ultra‐high performance magnetic field gradient subsystem (simultaneous 200‐mT/m gradient amplitude and 500‐T/m/s gradient slew rate; 1 MVA per axis [MAGNUS]) designed for neuroimaging with asymmetric transverse gradients and 4...

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Bibliographic Details
Published in:	Magnetic resonance in medicine Vol. 83; no. 1; pp. 352 - 366
Main Authors:	Tan, Ek T., Hua, Yihe, Fiveland, Eric W., Vermilyea, Mark E., Piel, Joseph E., Park, Keith J., Ho, Vincent B., Foo, Thomas K. F.
Format:	Journal Article
Language:	English
Published:	United States Wiley Subscription Services, Inc 01-01-2020
Subjects:	Adult Age Algorithms Amplitudes Brain Brain - diagnostic imaging Dependence diffusion imaging electric field Electric fields Electric Stimulation Equipment Design Female head‐only scanner Humans Image Processing, Computer-Assisted Magnetic Fields Magnetic Resonance Imaging Male Medical imaging microstructure Middle Aged MR safety Neuroimaging Neuroimaging - instrumentation Neuroimaging - methods Neurology Noise reduction peripheral nerve stimulation Peripheral nerves Peripheral Nerves - diagnostic imaging Peripheral Nerves - physiology Peripheral Nervous System - diagnostic imaging Phantoms, Imaging Reproducibility of Results Slew rate Stimulation Subsystems Thresholds Whole Body Imaging electric field microstructure MR safety diffusion imaging head-only scanner peripheral nerve stimulation
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Summary:	Purpose To establish peripheral nerve stimulation (PNS) thresholds for an ultra‐high performance magnetic field gradient subsystem (simultaneous 200‐mT/m gradient amplitude and 500‐T/m/s gradient slew rate; 1 MVA per axis [MAGNUS]) designed for neuroimaging with asymmetric transverse gradients and 42‐cm inner diameter, and to determine PNS threshold dependencies on gender, age, patient positioning within the gradient subsystem, and anatomical landmarks. Methods The MAGNUS head gradient was installed in a whole‐body 3T scanner with a custom 16‐rung bird‐cage transmit/receive RF coil compatible with phased‐array receiver brain coils. Twenty adult subjects (10 male, mean ± SD age = 40.4 ± 11.1 years) underwent the imaging and PNS study. The tests were repeated by displacing subject positions by 2‐4 cm in the superior–inferior and anterior–posterior directions. Results The x‐axis (left–right) yielded mostly facial stimulation, with mean ΔGmin = 111 ± 6 mT/m, chronaxie = 766 ± 76 µsec. The z‐axis (superior–inferior) yielded mostly chest/shoulder stimulation (123 ± 7 mT/m, 620 ± 62 µsec). Y‐axis (anterior–posterior) stimulation was negligible. X‐axis and z‐axis thresholds tended to increase with age, and there was negligible dependency with gender. Translation in the inferior and posterior directions tended to increase the x‐axis and z‐axis thresholds, respectively. Electric field simulations showed good agreement with the PNS results. Imaging at MAGNUS gradient performance with increased PNS threshold provided a 35% reduction in noise‐to‐diffusion contrast as compared with whole‐body performance (80 mT/m gradient amplitude, 200 T/m/sec gradient slew rate). Conclusion The PNS threshold of MAGNUS is significantly higher than that for whole‐body gradients, which allows for diffusion gradients with short rise times (under 1 msec), important for interrogating brain microstructure length scales.
Bibliography:	Funding information CDMRP W81XWH‐16‐2‐0054, NIH U01EB026976, NIH U01EB024450, NIH R01EB010065, and NIH R01CA190299. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0740-3194 1522-2594
DOI:	10.1002/mrm.27909