A quadrature lowpass birdcage coil for a vertical low field MRI Scanner.

Birdcage coils are widely used in magnetic resonance imaging (MRI) applications for their ability to operate in transmit/receive mode with high signal-to-noise ratio and wide homogeneous 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 as maximum value. In a previous article, the highpass birdcage coil was employed in a vertical bore MRI scanner by combining the sinusoidal and the end-ring resonant modes. In this article, we investigated the lowpass birdcage coil configuration to operate with a vertical bore MRI system, producing two B1 fields components perpendicular to the vertical B0 field. Its implementation is convenient because it requires one-half capacitors with respect to the highpass design. Moreover, at low field, the high near-electric field losses, which are the main disadvantage of the lowpass design, can be neglected. Experiments performed on a quadrature birdcage coil prototype mounted on an open MRI scanner showed that SNR and homogeneity degree increase with respect to the linear birdcage.