Cutoff-Free Traveling Wave NMR

TL;DR

This paper introduces a cutoff-free traveling wave NMR method using a transmission line with a central conductor, enabling broadband wave propagation for improved spectroscopy and imaging in various geometries.

Contribution

The authors develop a novel traveling wave NMR technique that eliminates the cutoff frequency limitation by using a transmission line, expanding the applicability of traveling wave MR.

Findings

Demonstrated broadband wave propagation in NMR using the new setup.

Achieved NMR spectra and images with genuine traveling wave behavior.

Enabled multinuclear and unconventional sample geometries in NMR experiments.

Abstract

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.