In vivo ¹ H MR spectroscopy with J-refocusing

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 (T_E ) was used, and a 90° J-refocusing pulse was inserted at T_E /2. Proton spectra were acquired at two T_E 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 T_E = 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 T_E . Higher signal amplitudes for glutamine, γ-aminobutyric acid and glutathione led to more reliable quantification precision for these metabolites. The refocused signal intensities at T_E = 68 ms were also unaffected by J-modulation but were smaller than the signals at T_E = 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 T_E is not possible while also providing more reliable quantification precision for J-coupled metabolites.