A high-sensitivity, high-B1 homogeneity probe for quantitation of metabolites

Accurate quantitation of metabolites in biological samples of irregular shape and inhomogeneous composition is generally acknowledged to be difficult. The difficulties are less pronounced with a probe having excellent B1 field homogeneity, high sensitivity, and a resonant frequency independent of sample size and composition. A prototype probe that aims to fulfill these requirements in wide-bore horizontal magnets is described. It comprises four separate tuned rings on a spherical surface which give a B1 field that is flat to +/- 1% over the design volume. Inter-ring coupling, and to a fifth ring used for matching, is by induction, and the mathematics of the tuning of the system are derived. It is shown that resonant frequency variation with sample size is negligible, and that the sensitivity closely approaches the theoretical limit.