Using simple electromagnetic analysis, we have demonstrated that it is important to use v  ×  B as the driving term when calculating the electric fields and currents induced in the body by rotational movements in a static magnetic field. We have also shown that it is necessary to take account of the volume charge density that is generated when the magnetic field and axis of rotation are not perpendicular in all locations. Analytic calculations of the electric field induced in a simple sphere rotating in a spatially uniform field and in a uniform field gradient showed that erroneous results are produced when the truncated driving term −(v  ·  ∇)A is used and/or the volume charge is neglected. Application of a BEM method to a simple, three-compartment model of the head also demonstrated that errors occur in field calculations in more complex systems when the incorrect, truncated driving term is used. These points should be fully considered in future modelling work used in the assessment of the effects of movement of patients and workers in and around magnetic resonance imaging equipment.

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