17O-Decoupled Proton MR Spectroscopy and Imaging in a Tissue Model

Abstract

17O-decoupled proton MR spectroscopy and imaging were implemented at 2 T. Their sensitivity and accuracyin vitrowere examined using semisolid tissue phantoms doped with H217O. A double-tuned solenoidal coil was used to irradiate the same volume of17O and1H nuclei, as well as to facilitate direct calibration of the decoupling power. Decoupling efficiency was optimized as was17O detection sensitivity. Decoupling was most efficient at RF amplitudes below 2.5 kHz (expressed as γ[17O] ×H1), which is within the limits of the acceptable specific absorption rate. Propagation of error analysis demonstrated that17O detection sensitivity is optimal at a TE equal to theT2of17O-depleted water protons. Based on Meiboom's work, a simple theory was formulated for estimating the transverse relaxivity of H217O and the proton signal enhancement produced by decoupling. There was excellent agreement between theory and experiment. Overall,17O-decoupled spectroscopy and imaging were highly sensitive and accurate in quantifying H217Oin vitro.