Electric Field Induced in Retina and Brain at Threshold Magnetic Flux Density Causing Magnetophosphenes

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In the international safety guidelines/standards, the rationale for human protection from extremely-low-frequency magnetic field exposure is to prevent the magneto-stimulation. The threshold in-situ electric field for magnetophosphenes has been experimentally derived as 8.14 mT at 20 Hz. However, the corresponding in-situ electric field in the central nervous system has not been well investigated. The present study derived computationally in-situ electric field in the brain and retina in different anatomically-based numeric human models exposed to uniform magnetic fields at extremely low frequencies. A quasi-static finite-difference time-domain method was applied to analyze this problem. First, the computational uncertainty caused by using a stair-casing model is investigated by comparing the electric field induced in a three-layer sphere obtained by the computational method to an analytical solution. In addition, the electric fields induced in anatomically-based models with different resolutions are also compared. For our computational results, the 99^<th> percentile value of the in-situ electric field is found to be reasonable both for the sphere and anatomically-based models with different resolutions. Then, the 99^<th> percentile values of the electric field in the brain and retina in different models are computed for exposure at the threshold magnetic flux density for magnetophosphenes. When comparing the 99^<th> percentile value in the brain of the anatomically-based model with those derived from an ellipsoid defined in the IEEE standard, the former was 10-70% larger than the latter. The main reason for this difference is attributed to the remaining part of the body in addition to the model inhomogeneity.
2011-05-19

Electric Field Induced in Retina and Brain at Threshold Magnetic Flux Density Causing Magnetophosphenes

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