title: Repeatability of (31) P MRSI in the human brain at 7 T with and without the nuclear Overhauser effect.
abstract: An often-employed strategy to enhance signals in (31) P MRS is the generation of the nuclear Overhauser effect (NOE) by saturation of the water resonance. However, NOE allegedly increases the variability of the (31) P data, because variation is reported in NOE enhancements. This would negate the signal-to-noise (SNR) gain it generates. We hypothesized that the variation in NOE enhancement values is not caused by the variability in NOE itself, but is attributable to measurement uncertainties in the values used to calculate the enhancement. If true, the expected increase in SNR with NOE would improve the repeatability of (31) P MRS measurements. To verify this hypothesis, a repeatability study of native and NOE-enhanced (31) P MRSI was performed in the brains of seven healthy volunteers at 7 T. The repeatability coefficient (RC) and the coefficient of variation in repeated measurements (CoVrepeat ) were determined for each method, and the 95% limits of agreement (LoAs) between native and NOE-enhanced signals were calculated. The variation between the methods, defined by the LoA, is at least as great as that predicted by the RC of each method. The sources of variation in NOE enhancements were determined using variance component analysis. In the seven metabolites with a positive NOE enhancement (nine metabolite resonances assessed), CoVrepeat improved, on average, by 15%. The LoAs could be explained by the RCs of the individual methods for the majority of the metabolites, generally confirming our hypothesis. Variation in NOE enhancement was mainly attributable to the factor repeat, but between-voxel effects were also present for phosphoethanolamine and (glycero)phosphocholine. CoVrepeat and fitting error were strongly correlated and improved with positive NOE. Our findings generally indicate that NOE enhances the signal of metabolites, improving the repeatability of metabolite measurements. Additional variability as a result of NOE was minimal. These findings encourage the use of NOE-enhanced (31) P MRSI. Copyright © 2015 John Wiley & Sons, Ltd.
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.
authors.forename: Miriam W
authors.initials: MW
authors.lastname: Lagemaat
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.
authors.forename: Bart L
authors.initials: BL
authors.lastname: van de Bank
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Pascal
authors.initials: P
authors.lastname: Sati
authors.affiliation: MRS Core Facility, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Shizhe
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.
authors.forename: Marnix C
authors.initials: MC
authors.lastname: Maas
authors.affiliation: Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.|Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.|Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany.
authors.forename: Tom W J
authors.initials: TW
authors.lastname: Scheenen
mesh_terms: D000328:Adult; D001921:Brain / Q000378:metabolism*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D055442:Metabolome; D010758:Phosphorus; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D010758:Phosphorus
keywords: 7 T; MRS; repeatability; reproducibility; ultrahigh field