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SYMR: Symposium Nuclear Magnetic Resonance: from Applications in Condensed-Matter Physics to New Frontiers

SYMR 4: SYMR Nuclear Magnetic Resonance: From Applications in Condensed Matter Physics to New Frontiers

SYMR 4.5: Hauptvortrag

Dienstag, 23. März 2010, 11:45–12:15, H1

Traveling-Wave MRI — •Klaas Prüßmann — Insitute for Biomedical Engineering, ETH and University of Zurich, Switzerland

High-field magnets of sufficient inner diameter permit the formation of axially traveling RF waves at NMR frequencies. Such traveling waves can be exploited to excite and detect NMR across large distances. This principle has been demonstrated in a wide-bore 7T magnet with an inner RF screen of 58 cm in diameter, using a patch antenna for RF transmission and reception. Proton NMR spectra of an ethanol solution have been obtained at antenna distances up to more than 3 m. In high-field MRI of humans the traveling-wave approach has the potential to improve RF uniformity, as illustrated by initial in-vivo results. The presentation will also include brief discussions of the reciprocity and efficiency of traveling-wave probes, wave impedance matching, and propagation-related phase delays. Finally it will address the feasibility of using multiple waveguide modes for establishing spatial diversity of RF fields, which underlies the practically important concepts of RF shimming and parallel MRI.