"Electromagnetc Fields In- Duced In a Solid Cylindrical Volume Conductor Due to Switching of Mri Z Gradient Field: Application to Peripheral Nerve Stimulation"
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Date
2018-06-18
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Addis Ababa University
Abstract
The rapid switching frequency of MRI gradient _elds has a direct relationship to
the resolution and hence to the quality of the image. Hence, there is a tendency in
the research area to increase the frequency of switching even more. However, the
rapid switching frequency can create unwanted peripheral nerve stimulation on the
patient's body due to the eddy current induction. In this report a model of the
induction of the magnetic and electric _elds as well as the eddy current in a solid
cylindrical volume conductor (human body model) due to the switching of the Z
gradient coils have been explored analytically. The coils are assumed to carry time
harmonic variable current at low frequency. For the analysis, Maxwell's Equations
are approximated for this quasi-static situation. Starting from the vector potential
expression and taking the _rst order asymptotic approximations of the modi_ed
Bessel functions, the solutions for the _eld vectors and the eddy current expression
in the cylinder have been found. The application of the problem to peripheral nerve
stimulation and the mechanism of PNS in the aspect of its useful application has
been discussed. The plot of the eddy current density against the radial distance
in the cylinder has shown that the peripheral nerve stimulation is con_ned to the
peripheral surface of the patient's body. The solutions have important implication
in the design of MRI gradient coils to avoid PNS during scanning and ensure
patient safety and comfort.
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Keywords
Solid Cylindrical, Peripheral Nerve Stimulation, Electromagnetc Fields