期刊
MAGNETIC RESONANCE IN MEDICINE
卷 83, 期 1, 页码 352-366出版社
WILEY
DOI: 10.1002/mrm.27909
关键词
diffusion imaging; electric field; head-only scanner; microstructure; MR safety; peripheral nerve stimulation
资金
- National Institute of Biomedical Imaging and Bioengineering [NIH U01EB024450]
- U.S. Department of Defense [CDMRP W81XWH-16-2-0054]
- National Institute of Neurological Disorders and Stroke [NIH U01EB026976]
- National Cancer Institute [NIH R01EB010065, NIH R01CA190299]
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 Delta G(min) = 111 +/- 6 mT/m, chronaxie = 766 +/- 76 mu sec. The z-axis (superior-inferior) yielded mostly chest/shoulder stimulation (123 +/- 7 mT/m, 620 +/- 62 mu sec). 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.
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