Phosphorus ((31) P) MRS is a powerful tool for the non-invasive investigation of human liver metabolism. Four in vivo (31) P localization approaches (single voxel image selected in vivo spectroscopy (3D-ISIS), slab selective 1D-ISIS, 2D chemical shift imaging (CSI), and 3D-CSI) with different voxel volumes and acquisition times were demonstrated in nine healthy volunteers. Localization techniques provided comparable signal-to-noise ratios normalized for voxel volume and acquisition time differences, Cramer-Rao lower bounds (8.7 ± 3.3%1D-ISIS , 7.6 ± 2.5%3D-ISIS , 8.6 ± 4.2%2D-CSI , 10.3 ± 2.7%3D-CSI ), and linewidths (50 ± 24 Hz1D-ISIS , 34 ± 10 Hz3D-ISIS , 33 ± 10 Hz2D-CSI , 34 ± 11 Hz3D-CSI ). Longitudinal (T1 ) relaxation times of human liver metabolites at 7 T were assessed by 1D-ISIS inversion recovery in the same volunteers (n = 9). T1 relaxation times of hepatic (31) P metabolites at 7 T were the following: phosphorylethanolamine - 4.41 ± 1.55 s; phosphorylcholine - 3.74 ± 1.31 s; inorganic phosphate - 0.70 ± 0.33 s; glycerol 3-phosphorylethanolamine - 6.19 ± 0.91 s; glycerol 3-phosphorylcholine - 5.94 ± 0.73 s; γ-adenosine triphosphate (ATP) - 0.50 ± 0.08 s; α-ATP - 0.46 ± 0.07 s; β-ATP - 0.56 ± 0.07 s. The improved spectral resolution at 7 T enabled separation of resonances in the phosphomonoester and phosphodiester spectral region as well as nicotinamide adenine dinucleotide and uridine diphosphoglucose signals. An additional resonance at 2.06 ppm previously assigned to phosphoenolpyruvate or phosphatidylcholine is also detectable. These are the first (31) P metabolite relaxation time measurements at 7 T in human liver, and they will help in the exploration of new, exciting questions in metabolic research with 7 T MR.
Keywords: 7 T; T1; human liver; localization; phosphorus; relaxation; spectroscopic imaging; spectroscopy.
Copyright © 2014 John Wiley & Sons, Ltd.