Naturaleza de los suelos arcillosos

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permittivity is increased. However, this assumes that the loss tangent remains low rela- tive to the body. For example, conductivities of 0.1, 0.5 and 1.0 S/m result in coil losses of 2.5, 11 and 19% respectively. These simulations show the importance of low-loss HPMs as the gains obtained in Figure 5.2f ) are of the same order of magnitude with losses from 0.5 S/m onward, nullifying the HPM’s effect.

One of the potential disadvantages of using integrated HPMs is the increase in weight of the array. The three-element integrated HPM coil in this paper has a mass of 760 grams, but this was not perceived as uncomfortable by any of the subjects in this study. This is in line with previous studies, where even larger amounts of HPM up to 4 kg on the chest have been used [26]. The use of integrated HPM coils would be much easier to realize in, for example, posterior body arrays integrated into the scanner bed. Weight can possibly be reduced by using water-based ceramics. Although their effectiveness has been shown in literature, their use in fully integrated HPM coils might be limited, as high relative permittivities (>300) are difficult to obtain and conductivities are often higher than 0.1 S/m [3, 4, 10].

5.5.

ACKNOWLEDGEMENTS

The authors would like to thank Wyger Brink for performing simulations relating to this work and for extended discussions. This work was funded by the ERC under grant num- ber 670629 and 737180, and by the NWO domain AES under grant number 13375.

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6

SUMMARY AND

GENERAL

DISCUSSION