Quadrature lowpass birdcage coil for low field open MRI scanner

The main goal of this research was to demonstrate the utility of using a quadrature birdcage coil in lowpass version for magnetic resonance imaging (MRI) in open scanner at very low static field. When used in horizontal bore MRI systems, the birdcage coil is able to produce circular polarized field using quadrature excitation, thus reaching SNR improvement of 2 as maximum value. The birdcage coil in high-pass version can be employed even in a vertical bore MRI scanner, by combining the sinusoidal and the end-ring resonant modes. In this paper we investigated the lowpass birdcage coil configuration to operate with a vertical bore MRI system, producing two 1B fields components perpendicular to the vertical B0 field. Its implementation is convenient because it requires one half capacitors with respect to the high-pass design. Moreover, at low field the high near-electric field losses, that represent the main disadvantage of the low pass design, can be neglected. Experiments performed on a quadrature birdcage coil prototype mounted on an open MRI scanner, showed that both SNR and homogeneity degree increase with respect to the linear birdcage.