Design and Implementation of Split-Leg Type Elliptical Whole-Body Birdcage RF Coil at 1.5 T MRI

Abstract

Featured Application An elliptical RF coil configuration can be implemented for whole-body imaging in a magnetic resonance imaging (MRI) system. Additionally, this elliptical configuration can be modified, and the space between the RF shield and the RF coil can be utilized for interventional radiological equipment systems such as PET detectors and HIFU transducers. The PET detector can be placed between the horizontal space between neighboring legs and the vertical space between the RF coil and the RF shield. Additionally, the HIFU transducer can be implemented for breast as well as prostate cancers, where the transducer is placed below the patient. The feasibility and the development of a four-port elliptical birdcage radio frequency (RF) coil for generating a homogenous RF magnetic (B-1) field is presented for a space-constrained narrow-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 B-1(+)-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 B-1(+)-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 B-1(+)-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 x 58 cm) were similar to those of a commercial circular birdcage (diameter, 58 cm), thereby indicating acceptable performance. 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.