  Recently, the concept of traveling-wave NMR/MRI was introduced by Brunner et
al. (Nature 457, 994-992 (2009)), who demonstrated MR images acquired using
radio frequency (RF) waves propagating down the bore of an MR scanner. One of
the significant limitations of this approach is that each bore has a specific
cutoff frequency, which can be higher than most Larmor frequencies of at the
magnetic field strengths commonly in use for MR imaging and spectroscopy today.
We overcome this limitation by using a central conductor in the waveguide and
thereby converting it to a transmission line (TL), which has no cutoff
frequency. Broadband propagation of waves through the sample thus becomes
possible. NMR spectra and images with such an arrangement are presented and
genuine traveling wave behavior is demonstrated. In addition to facilitating
NMR spectroscopy and imaging in smaller bores via traveling waves, this
approach also allows one to perform multinuclear traveling wave experiments (an
example of which is shown), and to study otherwise difficult-to-access samples
in unusual geometries.
