Improved RF Control of the Travelling Wave MR using a Multi-Mode Coaxial Waveguide

Anna Andreychenko¹, Hugo Kroeze¹, Peter Luijten¹, Jan J. W. Lagendijk¹, Cornelis A. T. van den Berg¹

A multi-transmit travelling wave setup with a coaxial feeding section capable of supporting several modes for optimal RF shimming performance is demonstrated. Selective mode excitation is performed in the feeding section at a distant location from the sample. The cut-off frequencies of higher order modes were decreased by placing a circular array of water tubes along the RF screen. Such a dielectrically lined waveguide can support surface modes with similar field patterns and B1+ efficiency as normal volume waveguide modes but are less susceptible to RF attenuation. This preserves B1+ control even at the distant locations from the feeding section