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

Abstract

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 parameters included permittivity variation in the substrate, substrate thickness, antenna length, and conductor geometry. We conducted electromagnetic simulations as well as phantom experiments to compare the transmit/receive performance 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 efficiency 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 uniform current distribution along its conductors. The nine-channel transmit/receive NODES array achieved 7.5% higher B + 1 homogeneity 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 elements and may provide improved transmit/receive performance for future ultrahigh field MRI applications.

Scaling the mountains: what lies above 7 Tesla magnetic resonance?

“…As we move up the mountain face, we should pause for a moment to acknowledge and applaud the pioneers who climbed the very steep mountains to 9.4 T [33], 10.5 T [8,37,38] and 11.7 T [39]. These explorers were essentially free climbing, reaching the summit without vendor-provided RF coils and without push-button software, yet nevertheless navigating through the enormous challenges towards beautiful images of the brain and the body enabled by parallel transmission.…”

Dipolectric antenna for high‐field MRI

“…Furthermore, ceramic materials can be currently developed in an impressively wide range of dielectric constants and electrical conductivities, and this should provide a motivation to explore such structures in the context of novel RF concepts tailored for different B 0 field strengths. Also, note that the dielectric block does not necessarily have to be designed as a homogeneous structure 37 ; mixing dielectric materials of different electrical properties could be considered as promising aspect of the future DRA optimizations. The same applies to the geometry of the dipole antenna and the distribution of the lumped components on the antenna.…”

Multi-feed, loop-dipole combined dielectric resonator antenna arrays for human brain MRI at 7 T

“…16 or 24), inter-element coupling can be problematic, and additional RF shields were used in their simulations. A similar approach was proposed by Sadeghi-Tarakameh et al who showed that combining dipole antennas with optimized dielectric blocks can be a promising solution for MRI at 10.5 T [26].…”