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This work focuses on the in silico evaluation of the energy deposed by MRI switched gradient fields in bulk metallic implants and the consequent temperature increase in the surrounding tissues. An original computational strategy, based on the subdivision of the gradient coil switching sequences into sub-signals and on the time-harmonic electromagnetic field solution, allows to realistically simulate the evolution of the phenomena produced by the gradient coils fed according to any MRI sequence. Then, Pennes’ bioheat equation is solved through a Douglas–Gunn time split scheme to compute the time-dependent temperature increase. The procedure is validated by comparison with laboratory results, using a component of a realistic hip implant embedded within a phantom, obtaining an agreement on the temperature increase better than 5%, lower than the overall measurement uncertainty. The heating generated inside the body of a patient with a unilateral hip implant when undergoing an Echo-Planar Imaging (EPI) MRI sequence is evaluated and the role of the parameters affecting the thermal results (body position, coil performing the frequency encoding, effects of thermoregulation) is discussed. The results show that the gradient coils can generate local increases of temperature up to some kelvin when acting without radiofrequency excitation. Hence, their contribution in general should not be disregarded when evaluating patients’ safety.

An experimental setup, made up of a three-limbed ferromagnetic core fitted with pickup coils, has been designed and built to be used as test bench for validation of magnetic field analysis with hysteresis. Unidirectional or rotational flux patterns and distorted waveforms can be generated by modifying the supply conditions of the coils. A detailed description of the structure with its supply and pickup coils is given. The analysis has been developed under different operating conditions. The experimental results of local and integral quantities are presented and compared with finite-element methods simulations.Index Terms-Finite-element methods (FEMs), hysteresis, magnetic analysis, magnetic measurements.