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Computation of Fields and SAR for MRI with FDTD Simulation

In most fields today, electronic devices must meet strict certification requirements to ensure that humans are not exposed to excessive levels of radiated energy. If sufficiently high levels of power, quantified as the Specific Absorption Rate (SAR), are dissipated in human tissue, the result could be tissue heating and damage. Should a device that has reached the prototyping stage fail to pass SAR certification, a redesign will be required, costing both time and money. Through advanced software tools, designs can be iterated and validated for compliance, ensuring a good product before any prototypes are built. To adequately analyze this type of design, a fully three-dimensional approach for simulating the propagation of electromagnetic fields is required.

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For a number of years, researchers in the MRI area have made use of FDTD simulation software for computing the fields internal to the body, which are nearly impossible to measure experimentally and to design structures such as coils. The simulation procedure allows the coil designer to get quick feedback on the performance of the device, without the time or cost of producing numerous prototypes. The further ability to simulate the structure in practical use, such as the coil around a body part, permits the designer to optimize the device under loaded conditions and ensure that the regulated limits such as SAR are within thresholds. In this article, a SAR analysis for an MRI system is presented using XFdtd 3D EM Simulation Software.