Ali Caglar Özen1,2, Michael Bock3, Ergin Atalar4. 1. Department of Radiology, Medical Physics, University Medical Center Freiburg, 79106, Freiburg, Germany. ali.oezen@uniklinik-freiburg.de. 2. Department of Electrical and Electronics Engineering, Bilkent University, 06800, Ankara, Turkey. ali.oezen@uniklinik-freiburg.de. 3. Department of Radiology, Medical Physics, University Medical Center Freiburg, 79106, Freiburg, Germany. 4. Department of Electrical and Electronics Engineering, Bilkent University, 06800, Ankara, Turkey.
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*. MATERIALS AND 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. CONCLUSION: CEA MRI can be implemented in clinical MRI systems using active decoupling with parallel transmit array capabilities with minor hardware modifications.
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*. MATERIALS AND 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. CONCLUSION: CEA MRI can be implemented in clinical MRI systems using active decoupling with parallel transmit array capabilities with minor hardware modifications.
Authors: Pascal P Stang; Steven M Conolly; Juan M Santos; John M Pauly; Greig C Scott Journal: IEEE Trans Med Imaging Date: 2011-09-26 Impact factor: 10.048