Convergence of optics and NMR: Far field imaging phenomena in magnetic resonance

In conventional NMR, near-field RF induction coils are used as the only excitation method to obtain images in clinical and research environments. At high-field strength (> 128 MHz), the propagation wave vector of the excitation field can no longer be ignored as the wavelength becomes comparable to the imaging volume, particularly if the medium dielectric constant is large. Here, we present our latest developments on a traveling wave transmission system that allows traveling wave mode propagation in a 698 MHz horizontal bore NMR imaging systems. The transmission system consists of a metal bore of the magnet and an acrylic tube filled with deionized water. The excitation of a waveguide is achieved through a transmit-receive loop coil probe placed at one or both ends of the guide. We report the first observation of fringes recorded in a resonant spin system arising from the interference of the propagating excitation field with its reflection at the end of the dielectric waveguide boundary. The implications for ultra-high field NMR include larger field of view imaging and potential for new mechanisms of image spatial encoding as well as spatial field inhomogeneity correction based on phase conjugate imaging and holographic principles.