A nine-channel transmit/receive array for spine imaging at 10.5 T: Introduction to a nonuniform dielectric substrate antenna

Abstract

Purpose: The purpose of this study is to introduce a new antenna element with improved transmit performance, named the nonuniform dielectric substrate(NODES) antenna, for building transmit arrays at ultrahigh- field.Methods: We optimized a dipole antenna at 10.5 Tesla by maximizing the B+1- SAR efficiency in a phantom for a human spine target. The optimization pa-rameters included permittivity variation in the substrate, substrate thickness, antenna length, and conductor geometry. We conducted electromagnetic simu-lations as well as phantom experiments to compare the transmit/receive perfor-mance of the proposed NODES antenna design with existing coil elements from the literature.Results: Single NODES element showed up to 18% and 30% higher B+1- SAR ef-ficiency than the fractionated dipole and loop elements, respectively. The new element is substantially shorter than a commonly used dipole, which enables z- stacked array formation; it is additionally capable of providing a relatively uni-form current distribution along its conductors. The nine- channel transmit/re-ceive NODES array achieved 7.5% higher B+1homogeneity than a loop array with the same number of elements. Excitation with the NODES array resulted in 33% lower peak 10g- averaged SAR and required 34% lower input power than the loop array for the target anatomy of the spine.Conclusion: In this study, we introduced a new RF coil element: the NODES antenna. NODES antenna outperformed the widely used loop and dipole ele-ments and may provide improved transmit/receive performance for future ultra-high field MRI applications.