Electromagnetc Fields In- Duced In A Solid Cylindrical Volume Conductor Due To Switching Of Mri Z Gradient Field Application To Peripheral Nerve Stimulation

The rapid switching frequency of MRI gradient _elds has a direct relationship tornthe resolution and hence to the quality of the image. Hence, there is a tendency inrnthe research area to increase the frequency of switching even more. However, thernrapid switching frequency can create unwanted peripheral nerve stimulation on thernpatient's body due to the eddy current induction. In this report a model of therninduction of the magnetic and electric _elds as well as the eddy current in a solidrncylindrical volume conductor (human body model) due to the switching of the Zrngradient coils have been explored analytically. The coils are assumed to carry timernharmonic variable current at low frequency. For the analysis, Maxwell's Equationsrnare approximated for this quasi-static situation. Starting from the vector potentialrnexpression and taking the _rst order asymptotic approximations of the modi_edrnBessel functions, the solutions for the _eld vectors and the eddy current expressionrnin the cylinder have been found. The application of the problem to peripheral nervernstimulation and the mechanism of PNS in the aspect of its useful application hasrnbeen discussed. The plot of the eddy current density against the radial distancernin the cylinder has shown that the peripheral nerve stimulation is con_ned to thernperipheral surface of the patient's body. The solutions have important implicationrnin the design of MRI gradient coils to avoid PNS during scanning and ensurernpatient safety and comfort.

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