title: Active decoupling of RF coils using a transmit array system.
abstract: OBJECTIVE
  Implementation of a decoupling method for isolation of transmit and receive radio frequency (RF) coils for concurrent excitation and acquisition (CEA) MRI in samples with ultra-short T2*.
  
  
  METHODS
  The new phase and amplitude (PA) decoupling method is implemented in a clinical 3T-MRI system equipped with a parallel transmit array system. For RF excitation, two transmit coils are used in combination with a single receive coil. The transmit coil is geometrically decoupled from the receive coil, and the remaining B 1-induced voltages in the receive coil during CEA are minimized by the second transmit coil using a careful adjustment of the phase and amplitude settings in this coil. Isolation of the decoupling scheme and transmit noise behavior are analyzed for different loading conditions, and a CEA MRI experiment is performed in a rubber phantom with sub-millisecond T2* and in an ex vivo animal.
  
  
  RESULTS
  Geometrical (20 dB) and PA decoupling (50 dB) provided a total isolation of 70 dB between the transmit and receive coils. Integration of a low-noise RF amplifier was necessary to minimize RF transmit noise. CEA MR images could be reconstructed from a rubber phantom and an ex vivo animal.
  
  
  CONCLUSIONS
  CEA MRI can be implemented in clinical MRI systems using active decoupling with parallel transmit array capabilities with minor hardware modifications.
authors.affiliation: Department of Radiology, Medical Physics, University Medical Center Freiburg, 79106, Freiburg, Germany. ali.oezen@uniklinik-freiburg.de.|Department of Electrical and Electronics Engineering, Bilkent University, 06800, Ankara, Turkey. ali.oezen@uniklinik-freiburg.de.
authors.forename: Ali Caglar
authors.identifier: http://orcid.org/0000-0003-3536-0826
authors.initials: AC
authors.lastname: Özen
authors.affiliation: Department of Radiology, Medical Physics, University Medical Center Freiburg, 79106, Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Bock
authors.affiliation: Department of Electrical and Electronics Engineering, Bilkent University, 06800, Ankara, Turkey.
authors.forename: Ergin
authors.initials: E
authors.lastname: Atalar
mesh_terms: D000669:Amplifiers, Electronic; D004867:Equipment Design; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011846:Radio Waves
keywords: Concurrent excitation and acquisition; Continuous-wave NMR; Geometrical decoupling; Phase amplitude decoupling; Transmit array