Analysis of Conservative and Magnetically Induced Electric Fields in a Low-Frequency Birdcage Coil

DOI: 10.4236/jemaa.2013.57043   PDF   HTML     3,798 Downloads   5,581 Views   Citations


Numerical methods are used to evaluate variations of the electromagnetic fields generated by a head-sized birdcage coil as a function of load (“loading effect”). The loading effect was analyzed for the cases of a coil loaded with a conductive cylindrical sample, a dielectric cylindrical sample, and an anatomically precise head model. Maxwell equations were solved by means of finite difference time domain (FDTD) method conducted at 12.8, 64, and 128 MHz. Simulation results indicate that at 12.8 MHz the conservative electric field (Ec) caused by the scalar electric potentials between the coil and the load or within the load was significantly higher than the magnetically-induced electric field (Ei) and was the major component of the total electric field (Etotal). The amplitudes of Ec and Etotal are seen to be lower within a sample than at a corresponding location in an empty coil, but approximately 65% higher in the space between coil and sample than at a corresponding location in an empty coil. This is due to polarization effects generating an additional scalar potential parallel to the original field. The increased electric field between coil and sample may cause increased power deposition at the surface of the sample and may affect the RF-induced currents in external leads used for physiological recording, i.e. ECG, during MRI scanning.

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B. Park, S. Rajan, C. Collins and L. Angelone, "Analysis of Conservative and Magnetically Induced Electric Fields in a Low-Frequency Birdcage Coil," Journal of Electromagnetic Analysis and Applications, Vol. 5 No. 7, 2013, pp. 271-280. doi: 10.4236/jemaa.2013.57043.

Conflicts of Interest

The authors declare no conflicts of interest.


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