Metamaterial Media for MRI Applications

Introduction Metamaterials are artificial composites whose electromagnetic properties can be engineered to achieve phenomena not observed in natural materials [1]. They are usually manufactured by means of the repetition of resonant elements to constitute a periodic structure and an essential characteristic is that an effective permittivity and permeability (μ) can be defined through the appropriate homogenization procedure [2]. Application of the metamaterials in MRI has been previously explored in several works [3-7]. Basically, two types of metamaterials which correspond to two different resonant elements have been used: swiss rolls [3-5] and capacitively-loaded split rings [6–7]. Split rings have the major advantage over swiss rolls of providing three-dimensional isotropy when they form a cubic lattice. In previous works [6-7], a slab of split-ring metamaterial with μ=-1 was shown, which behaves as a superlens with subwavelength resolution [1] for the radiofrequency (RF) magnetic field of a 1.5T system. In the present work, we explore the application of split-ring metamaterials with different permeability values, in particular, slabs with zero permeability (μ=0) and high permeability (μ=∞), which will reject and confine, respectively, the RF magnetic field. These slabs have been designed to work at 63.6 MHz, and their applications on MRI experiments evaluated at 1.5 T.