Single-feed quadrature coils as transceiver array elements for improved SNR and transmit efficiency

INTRODUCTION: Quadrature or circularly polarized (CP) coils are desired in MR experiments due to their improved MR sensitivity (by 40%) and reduced excitation power (by half) compared with linear coils. This is particularly true in parallel imaging and parallel excitation where the reception/excitation acceleration demands highly efficient receive and transmit. Conventionally quadrature coils are driven from two feeding ports. In surface coils, which usually serve as resonant elements in parallel imaging coil arrays, the quadrature mode is usually formed by using two loops orthogonal to each other. Their bulky structure limits their application to designing parallel imaging arrays. Soutome and co-worker proposed a method for single-feed birdcage coil and demonstrated its feasibility at 1.5T (1). In this work, we propose a method to generating quadrature modes by single-feed surface coil for high field MR applications. This method is based on the single-feed CP microstrip patch resonator technology. To demonstrate the concept, a single-feed quadrature coil array with two elements was designed and evaluated by using FDTD simulation and bench test.