In vivo 1 H MR spectroscopy with J-refocusing.

Abstract

The goal of this study was to propose a novel localized proton MR spectroscopy (MRS) sequence that reduces signal loss due to J-modulation in the rat brain in vivo. Sprague-Dawley rats were studied at 9.4 T. A semi-LASER sequence with evenly distributed echo-time (TE ) was used, and a 90° J-refocusing pulse was inserted at TE /2. Proton spectra were acquired at two TE s (30 and 68 ms), with and without the J-refocused pulse. Data were processed in MATLAB and quantified with LCModel. The J-refocused spectrum acquired at TE = 30 ms did not show any signal losses due to J-modulation and had comparable spectral pattern to the one acquired with semi-LASER using the minimum achievable TE . Higher signal amplitudes for glutamine, γ-aminobutyric acid and glutathione led to more reliable quantification precision for these metabolites. The refocused signal intensities at TE = 68 ms were also unaffected by J-modulation but were smaller than the signals at TE = 30 ms mainly due to transverse T2 relaxation of metabolites. The proposed localized MRS sequence will be beneficial in both animal and human MRS studies when using ultra-short TE is not possible while also providing more reliable quantification precision for J-coupled metabolites.