Sensitivity and localization enhancement in multinuclear in vivo NMR spectroscopy by outer volume presaturation

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Abstract
Sampling of the entire brain tissue in 1H NMR metabolic studies is complicated by the presence of intense pericranial lipid and tissue water resonances, which can obscure metabolite resonances. This study extends the concept of localization by outer volume suppression (OVS) to achieve fully conformal in viuo localization, sampling at least 95% of rat brain with complete elimination of pericranial lipids. This has permitted acquisition of lipid-free short echo time (7.5 ms), high spatial resolution 2D spectroscopic images exhibiting high sensitivity and information content in relatively short measurement time (68 min). Incorporation of spatially tailored OVS into existing methods (e.g., DRESS, STEAM, PRESS) extends their localization efficiency and performance. Two single spin-echo localization sequences have been described that attain much shorter echo times or achieve better water suppression than PRESS. One of these sequences allows editing and relaxo-metric studies of J-coupled spins. The methods described are suitable for in vivo localization of most tissues and can be applied with any biologically important nucleus.