New method for the simultaneous detection of metabolites and water in localized in vivo 1H nuclear magnetic resonance spectroscopy

A new two-scan method for localized 1H in vivo NMR spectroscopy (MRS) without water suppression (WS) is described. In one of the scans, two chemical shift selective 180 degrees pulses are applied prior to a standard localization sequence to invert all metabolite signals upfield and downfield from water, which remains unaffected. The difference spectrum records the metabolites whereas water and accompanying gradient induced artifacts are widely suppressed. The method was implemented on a 4.7-T system using point resolved spectroscopy with a short echo time of 18 ms. Phantom measurements proved the feasibility of absolute quantification using water as an internal reference. Measurements on healthy rat brain yielded comparable spectrum quality as measurements with water presaturation. The method does not require additional adjustments or sophisticated data postprocessing and scales favorably with increasing B(0) field. Therefore, the method should be useful for 1H MRS without WS. Although the two-step method doubles the minimum total measurement time, it may also be of interest for spectroscopic imaging (SI) without WS, in particular if fast SI techniques are applied.