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High‐field actively detuneable transverse electromagnetic (TEM) coil with low‐bias voltage for high‐power RF transmission
Author(s) -
Avdievich Nikolai I.,
Bradshaw Ken,
Kuznetsov Andrey M.,
Hetherington Hoby P.
Publication year - 2007
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21242
Subject(s) - electromagnetic coil , rogowski coil , voltage , coil noise , physics , transformer , biasing , electrical impedance , coil tap , diode , high voltage , electrical engineering , optics , nuclear magnetic resonance , electronic circuit , transverse plane , materials science , rf power amplifier , optoelectronics , engineering , amplifier , structural engineering , cmos
The design and construction of a 4T (170 MHz) transverse electromagnetic (TEM) actively detuneable quadrature head coil is described. Conventional schemes for active detuning require high negative bias voltages (>300 V) to prevent leakage of RF pulses with amplitudes of 1–2 kW. To extend the power handling capacity and avoid the use of high DC bias voltages, we developed an alternate method of detuning the volume coil. In this method the PIN diodes in the detuning circuits are shorted when the RF volume coil is tuned, and negatively biased with –12 V when the coil is detuned. To preserve the high Q U / Q L ratio of the TEM coil, we modified the method of Nabetani and Watkins (Proceedings of the 13th Annual Meeting of ISMRM, Kyoto, Japan, 2004, abstract 1574) by utilizing a high‐impedance (∼200 Ω), lumped‐element, quarter‐wavelength transformer. A Q U of 500 was achieved for the detuneable TEM, such that incorporation of the detuning network had minimal effect (<1 dB) on the performance of the coil in vivo. Magn Reson Med 57:1190–1195, 2007. © 2007 Wiley‐Liss, Inc.