Transmit/receive radiofrequency coil with individually shielded elements.
A novel method for decoupling coil elements of transmit/receive (transceive) arrays is reported. Each element of a coil array is shielded both concentrically and radially to reduce the magnetic flux linkage between neighboring coils; this substantially reduces the mutual inductance between coil elements and allows them to behave independently. A six-channel transceive coil was developed using this decoupling scheme and compared with two conventional decoupling schemes: the partial overlapping of adjacent elements and capacitive decoupling. The radiofrequency coils were designed to image the human head and were tested on a 7-T Varian scanner. The decoupling, transmit uniformity, transmit efficiency, signal-to-noise ratio, and geometry factors were compared between coils. The individually shielded coil achieved higher minimum isolation between elements (2.7-4.0 dB) and lower geometry factors (2-14%) than the overlapped and capacitively decoupled coils, while showing a reduction in transmit efficiency (2.8-5.9 dB) and signal-to-noise ratio (up to 34%). No difference was found in the power absorbed by the sample during a 90° radiofrequency pulse. The inset distance of coil elements within their shields was then reduced, resulting in significant improvement of the transmit efficiency (1.3 dB) and signal-to-noise ratio (28%). The greatest asset of this decoupling method lies in its versatility: transceive coils can be created with elements of arbitrary shape, size, location, and resonant frequency to produce three-dimensional conformal arrays.
Gilbert
Kyle M
KM
Centre for Functional and Metabolic Mapping, Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada. kgilbert@imaging.robarts.ca
Curtis
Andrew T
AT
Gati
Joseph S
JS
Klassen
L Martyn
LM
Villemaire
Lauren E
LE
Menon
Ravi S
RS
D001931:Brain Mapping / Q000379:methods*; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011846:Radio Waves