Compact metamaterial-inspired RF coil based on split-ring resonators to enhance the magnetic field for 1.5T magnetic resonance imaging

In this paper, we propose a metamaterial-inspired RF coil structure based on a multiple split-ring resonator (MSRR) for 1.5T MRI. An additional component that enables to enhance the magnetic field of RF coil is proposed. This novel component is incorporated an array of split-rings and a central feature combined with square and circular rings (SC). By aligning the component with the split-ring resonator (SRR) in a coplanar arrangement, we derive a compact MSRR equipped with the SC structure (SC MSRR). We analyze the effect of different numbers of split rings within the component and the distance from the feed coil on gain of the magnetic field. The results indicate that the proposed metamaterial-inspired structure can effectively improve the near-field properties of the coil. The proposed SC MSRR has enhanced B-1(-) field strength effectively and keeps a lower specific absorption rate (SAR) level in the field of view (FOV), resulting in a significant increase in SAR efficiency and received sensitivity. Compared with the conventional SRR surface coil, the peak B-1(-) field strength can be enhanced by 3.15 times in the case of using SC MSRR, the peak SAR can be reduced by 20.14 % and the peak SAR efficiency can be improved 3.60 times. In addition, the proposed 4-channel head array consisting of SC MSRRs efficiently generates a higher quality B-1(-) field compared to the standard head birdcage coil. The high directivity of the metamaterial-inspired structure allows for good isolation between ports/channels. The high compactness and excellent performance of the SC MSRR prove that it can be an efficient candidate for the surface coil and high density array. This approach provides a new practical way to combine RF coils with metamaterials for MRI applications.