Folded‐end dipole transceiver array for human whole‐brain imaging at 7 T

• Published in: NMR in biomedicine 2021-08, Vol.34 (8), p.e4541-n/a
• Main Authors: Avdievich, Nikolai I., Solomakha, Georgiy, Ruhm, Loreen, Nikulin, Anton V., Magill, Arthur W., Scheffler, Klaus
• Format: Article
• Language: English
• Subjects: Antenna arrays; array optimization; Biological products; Brain; Brain - diagnostic imaging; Brain Mapping; Circular polarization; Computer Simulation; Decoupling; Design; Dipole antennas; Electromagnetic Fields; folded‐end dipole; human head imaging; Humans; Magnetic resonance imaging; Magnetic Resonance Imaging - instrumentation; Medical imaging; Neuroimaging; Quadratures; Radio frequency; Therapeutic applications; transceiver array; Transceivers; ultrahigh field MRI
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.4541

The advancement of clinical applications of ultrahigh field (UHF) MRI depends heavily on advances in technology, including the development of new radiofrequency (RF) coil designs. Currently, the number of commercially available 7 T head RF coils is rather limited, implying a need to develop novel RF head coil designs that offer superior transmit and receive performance. RF coils to be used for clinical applications must be robust and reliable. In particular, for transmit arrays, if a transmit channel fails the local specific absorption rate may increase, significantly increasing local tissue heating. Recently, dipole antennas have been proposed and used to design UHF head transmit and receive arrays. The dipole provides a unique simplicity while offering comparable transmit efficiency and signal‐to‐noise ratio with the conventional loop design. Recently, we developed a novel array design in our laboratory using a folded‐end dipole antenna. In this work, we developed, constructed and evaluated an eight‐element transceiver bent folded‐end dipole array for human head imaging at 7 T. Driven in the quadrature circularly polarized mode, the array demonstrated more than 20% higher transmit efficiency and significantly better whole‐brain coverage than that provided by a widely used commercial array. In addition, we evaluated passive dipole antennas for decoupling the proposed array. We demonstrated that in contrast to the common unfolded dipole array, the passive dipoles moved away from the sample not only minimize coupling between the adjacent folded‐end active dipoles but also produce practically no destructive interference with the quadrature mode of the array. An eight‐element transceiver bent folded‐end dipole array for human head imaging at 7 T was developed. Driven in the quadrature mode, the array demonstrated more than 20% higher transmit efficiency and significantly better whole‐brain coverage than that provided by a widely used commercial array. We demonstrated that in contrast to the common dipole array, the passive decoupling dipoles not only minimize coupling between the adjacent active dipoles but also produce minimal destructive interference with the quadrature mode of the array.