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  • Title: Physiologic effects of intense MR imaging gradient fields.
    Author: Bourland JD, Nyenhuis JA, Schaefer DJ.
    Journal: Neuroimaging Clin N Am; 1999 May; 9(2):363-77. PubMed ID: 10318720.
    Abstract:
    The strength duration relationship for peripheral nerve stimulation by MR imaging pulsed gradient magnetic fields was measured in 84 human subjects. The data were fitted to the hyperbolic strength-duration relationship: dB/dt=b(1 + c/d), where b is rheobase, c is chronaxie, and d is duration, and dB/dt is reported as the maximal value on the axis of the bore. For sensation threshold, average (b,c) (15 T/s, 0.37 ms) for the y-gradient and (26 T/s, 0.38 ms) for the z-gradient coil. The dB/dt intensity to induce a sensation which the subject described as uncomfortable was about 50% above the sensation threshold. Experiments with dogs showed that the cardiac stimulation by pulsed magnetic gradient fields is exceedingly unlikely.
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