Design and implementation of split‐leg type elliptical whole‐body birdcage rf coil at 1.5 t mri

Abstract

The feasibility and the development of a four‐port elliptical birdcage radio frequency (RF) coil for generating a homogenous RF magnetic (B1) field is presented for a space‐constrained nar-row‐bore magnetic resonance imaging (MRI) system. Optimization was performed for the elliptical birdcage RF coil by adjusting the position and the structure of the legs to maximize the B1+‐field uniformity. Electromagnetic (EM) simulations based on RF coil circuit co‐simulations were performed on a cylindrical uniform phantom and a three‐dimensional human model to evaluate the B1+‐field uniformity, the transmission efficiency, and the specific absorption rate (SAR) deposition. An elliptical birdcage RF coil was constructed, and its performance was evaluated through network analysis measurements such as S‐parameters and Q‐factor. Quadrature transmit and receive MRI experiments were conducted using both phantom and in vivo human for validation. The EM simulation results indicate reasonable B1+‐field uniformity and transmission efficiency for the proposed elliptical birdcage RF coil. The signal‐to‐noise ratio and the flip angle maps of the uniform phantom and the in vivo human MR images acquired using an elliptical birdcage (62 cm × 58 cm) were similar to those of a commercial circular birdcage (diameter, 58 cm), thereby indicating acceptable perfor-mance. In conclusion, the proposed split‐type asymmetric elliptical birdcage RF coil is useful for whole‐body MRI applications and can be used for imaging larger human subjects comfortably in a spacious imaging space.