title: Resolution improvements in in vivo 1H NMR spectra with increased magnetic field strength.
abstract: The measurement of cerebral metabolites using highly homologous localization techniques and similar shimming methods was performed in the human 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 cerebral glutamine content were clearly observed at 4 T compared to 1.5 T in 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 potential 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 as 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 field strength increases spectral resolution also for 1H NMR, which can lead to more than linear sensitivity gains.
authors.affiliation: Department of Radiology, University of Minnesota, Minneapolis, Minnesota, 55112, USA.
authors.forename: R
authors.initials: R
authors.lastname: Gruetter
authors.forename: S A
authors.initials: SA
authors.lastname: Weisdorf
authors.forename: V
authors.initials: V
authors.lastname: Rajanayagan
authors.forename: M
authors.initials: M
authors.lastname: Terpstra
authors.forename: H
authors.initials: H
authors.lastname: Merkle
authors.forename: C L
authors.initials: CL
authors.lastname: Truwit
authors.forename: M
authors.initials: M
authors.lastname: Garwood
authors.forename: S L
authors.initials: SL
authors.lastname: Nyberg
authors.forename: K
authors.initials: K
authors.lastname: Uğurbil
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001923:Brain Chemistry; D004285:Dogs; D006501:Hepatic Encephalopathy / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007294:Inositol / Q000032:analysis; D019344:Lactic Acid / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy; D011522:Protons; D051381:Rats; D015203:Reproducibility of Results; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D011522:Protons; C009217:scyllitol; D019344:Lactic Acid; D007294:Inositol