Reliable detection of macromolecules in single-volume H-1 NMR spectra of the human brain

In short echo time proton MR spectra of the brain, resonances from macromol ecules are visible. The macromolecular resonances in the 0.5-2.0 ppm region can be affected by lipid contamination arising from fat-containing regions outside the selected volume of interest (VOI) This study demonstrates that considerable lipid contamination may remain in stimulated echo acquisition mode (STEAM) spectra even if the spoiling of unwanted coherences is suffic ient and the VOI is placed 2 cm or more away from fat-containing regions, T he observed contamination was attributed to residual remote out-of-volume e xcitation, although only very small out-of-slice ripples of less than 0.2% of the in-slice excitation were found in the calculated excitation profile of the RF pulses. Spatial presaturation of fat-containing regions led to a sufficient suppression of the contamination and enabled the detection of hi ghly reproducible macromolecular resonances, Thus, in single-volume spectro scopy as well as in spectroscopic imaging (SI or CSI), the combination of v olume selection and outer volume presaturation, each in three dimensions, i s highly recommended to ensure accurate detection and reliable evaluation o f even small pathological alterations in macromolecules, e.g., proteins or lipids, or ct her resonances in the 0.5-2.0 ppm region. (C) 2001 WiIey-Liss , Inc.