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

Nikolai I. Avdievich, Georgiy Solomakha, Loreen Ruhm, Anke Henning, Klaus Scheffler

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)581-597
Number of pages17
JournalMagnetic resonance in medicine
Volume86
Issue number1
DOIs
StateAccepted/In press - 2021

Keywords

  • RF head array
  • decoupling of the transmit dipoles
  • folded-end dipole antenna
  • transceiver array
  • ultra-high field MRI
  • whole-brain coverage

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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