MR spectroscopy using multi-ring surface coils

A spatially uniform B-1-field is preferred for MR imaging and spectroscopy. Unfortunately, volume coils are sometimes unavailable, or do not provide a dequate RF power or SNR for some applications. In quantitative MRS, mean me tabolite concentration cannot be evaluated when the coil response is nonuni form, unless an assumption is made concerning the metabolite spatial distri bution. It is well known that standard single-loop surface coils, although offering high SNR characteristics, have poor B-1 homogeneity. New multi-rin g surface coils are proposed which produce a locally uniform B-1 field, wit h sensitivity and power requirements comparable to those of standard surfac e coils. MR spectroscopy using two and three-ring versions of this "local v olume coil" result in spatial localization essentially identical to that ob tained with a volume coil but with much improved RF power and SNR character istics. When compared to standard surface coils, the multi-ring coil offers much improved water suppression and localization, as well as reduced outer voxel contamination, with only a small loss in SNR and moderate increase i n SAR. In summary, the multi-ring coil operates midway between the volume c oil and the standard surface coil, retaining the most advantageous properti es of both. Magn Reson Med 42:655-664, 1999. Published 1999 Wiley-Liss, Inc .dagger