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In Ultra-High Field MRI systems, e.g. for B0 beyond 7 T, the performance of the RF coils is essential to provide a great image quality with a reasonable B1-field homogeneity in the imaging area, low SARs in the biological tissues and a good signal to noise ratio (SNR). Despite the many advantages in increasing the B0-field strength (higher resolution and SNR, reduced scan time), operating at higher frequencies adds significant technical complexity to NMR experiments and consequently to the RF coils design. As frequencies increase, the wavelength shortens (60 cm in the vacuum and 8.5 cm inside the head at 500 MHz), and becomes comparable to the electrical dimensions of the head/body and the RF coil. RF fields interact more strongly with human tissues and wave behaviour of the B1-field should affect strongly its homogeneity inside the highly permittive and lossy tissues. While B1 inhomogeneities cause non uniform intensity distribution in MR images, the RF electric field counterpart, potentially inhomogeneous too, should expose biological tissues to an excessive RF power deposition with induced local heating. Coupled to detailed anatomical human models, computational methods offer an indispensible tool for the investigation of the distribution of the magnetic field or the maximum local SAR values inside the tissues and for the design and evaluation of the RF coils' performance.

This article provides a summary of the work carried out by CEA Saclay, France using CST MICROWAVE STUDIO (CST MWS) and the HUGO Dataset with the permission and courtesy of Xavier Hanus and his colleagues.

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•Application Note: Electromagnetic Field And SAR Computation In A Human Head With RF Coil