Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 62, Issue 3, Pages 763-770Publisher
WILEY
DOI: 10.1002/mrm.22050
Keywords
planar gradients; gradient systems; magnetic resonance imaging; peripheral nerve stimulation
Funding
- National Institutes of Health [R01 RR15396]
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In MRI, strong, rapidly switched gradient fields are desirable because they can be used to reduce imaging time, obtain images with better resolution, or improve image signal-to-noise ratios. Improvements in gradient strength can be made by either increasing the gradient amplifier strength or by enhancing gradient efficiency. Unfortunately, many MRI pulse sequences, in combination with high-performance amplifiers and ex sting gradient hardware, can cause peripheral nerve stimulation (PNS). This makes improvements in gradient amplifiers ineffective at increasing safely usable gradient strength. Customized gradient coils are one way to achieve significant improvements in gradient performance. One specific gradient configuration, a planar gradient system, promises improved gradient strength and switching time for cardiac imaging. The PNS thresholds for planar gradients were characterized through human stimulation experiments on all three gradient axes. The specialized gradient was shown to have significantly higher stimulation thresholds than traditional cylindrical designs (y-axis SRmin = 210 +/- 18 mT/m/ms and Delta G(min) = 133 +/- 13 mT/m; x-axis SRmin = 222 +/- 24 mT/m/ms and Delta G(min) = 147 +/- 17 mT/m; z-axis SRmin = 252 +/- 26 mT/m/ms and Delta G(min) = 218 +/- 26 mT/m). This system could be operated at gradient strengths 2 to 3 times higher than cylindrical configurations without causing stimulation. Magn Reson Med 62:763-770, 2009. (C) 2009 Wiley-Liss, Inc.
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