Electromagnetic bandgap metasurfaces for decoupling of elements of MRI body coil array at 7 Tesla

摘要

Electromagnetic bandgap (EBG) structures belong to an important class of metamaterials that prevent wave propagation at certain frequencies. One of promising application areas of such structures is magnetic resonance imaging (MRI). Nowadays MRI technology develops towards using higher static magnetic field strengths. Particularly, development of novel receive and transmit body arrays for prospective 7T machines operating at 298 MHz is of a great importance. Such devices allow achieving higher image resolution and better diagnostic accuracy. As an alternative to conventional magnetic coils electric dipole antennas were recently proposed in order to reduce SAR keeping a high penetration depth and field uniformity. One of challenges in using dipole antennas as array elements in MRI is their strong mutual coupling, which lowers the useful signal. In the present work we test EBG metasurfaces with highly miniaturized unit cells for suppression of the coupling between two closely spaced dipole antenna elements of a 7T MRI body coil array. Meta-surface samples were optimized by means of numerical simulations and manufactured as multi-layered structures containing PCB-boards. The metasurface samples improve isolation of matched dipoles by up to -6 dB even for the dipole separation of λ/12. The isolation improvement provided by the manufactured metasurface samples was tested experimentally in the presence of a phantom (an equivalent of a human body).