RESOLUTION IMPROVEMENTS IN IN-VIVO H-1-NMR SPECTRA WITH INCREASED MAGNETIC-FIELD STRENGTH

The measurement of cerebral metabolites using highly homologous locali zation techniques and similar shimming methods was performed in the hu man brain at 1.5 and 4 T as well as in the dog and rat brain at 9.4 T. In rat brain, improved resolution was achieved by shimming all first- and second-order shim coils using a fully adiabatic FASTMAP sequence. The spectra showed a clear improvement in spectral resolution for all metabolite resonances with increased field strength. Changes in cereb ral glutamine content were clearly observed at 4 T compared to 1.5 T i n patients with hepatic encephalopathy. At 9.4 T, glutamine H4 at 2.46 ppm was fully resolved from glutamate H4 at 2.37 ppm, as was the pote ntial resonance from gamma-amino-butyric acid at 2.30 ppm and N-acetyl -aspartyl-glutamate at 2.05 ppm. Singlet linewidths were found to be a s low as 6 Hz (0.015 ppm) at 9.4 T, indicating a substantial decrease in ppm linewidth with field strength. Furthermore, the methylene peak of creatine was partially resolved from phosphocreatine, indicating a close to 1:1 relationship in gray matter. We conclude that increasing the magnetic held strength increases spectral resolution also for H-1 NMR, which can lead to more than linear sensitivity gains. (C) 1998 Ac ademic Press.