Unshielded bent folded‐end dipole 9.4 T human head transceiver array decoupled using modified passive dipoles

• Published in: Magnetic resonance in medicine 2021-07, Vol.86 (1), p.581-597
• Main Authors: Avdievich, Nikolai I., Solomakha, Georgiy, Ruhm, Loreen, Henning, Anke, Scheffler, Klaus
• Format: Article
• Language: English
• Subjects: Antenna arrays; Decoupling method; decoupling of the transmit dipoles; Design modifications; Dipole antennas; folded‐end dipole antenna; Interference; Neuroimaging; RF head array; transceiver array; Transceivers; ultra‐high field MRI; whole‐brain coverage
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.28711

Purpose To develop an unshielded dipole transceiver array for human head imaging at 9.4 Tesla and to improve decoupling of adjacent dipole elements, a novel array design with modified passive dipole antennas was developed, evaluated, and tested. Methods The new array consisted of 8 bent folded‐end dipole elements placed in a single row and surrounding the head. Adjacent elements of RF transceiver arrays are usually decoupled by introducing circuits electrically connected to elements. These methods are difficult to use for dipole arrays because of the distant location of the adjacent antennas. A recently developed decoupling technique using passive dipoles is simple and does not require any electrical connection. However, common parallel passive dipoles can produce destructive interference with the RF field of the array itself. To minimize this interference, we placed the passive dipoles perpendicularly to the active dipoles and positioned them at the ends of the array. We also evaluated the effect of different passive dipoles on the array transmit performance. Finally, we optimized the array transmit performance by varying the length of the dipole folded portion. Results By rotating the passive dipoles 90º and moving them toward the ends of the array, we minimized the destructive interference to an acceptable level without compromising decoupling and the transmit efficiency. Conclusion While keeping the benefits of the passive dipole decoupling method, the new modified dipoles produce substantially less destructive interference with the RF field of the array than the common design. The constructed transceiver array demonstrated good decoupling and whole‐brain coverage.