Absolute Quantification of Phosphor‐Containing Metabolites in the Liver Using (31)P MRSI and Hepatic Lipid Volume Correction at 7T Suggests No Dependence on Body Mass Index or Age

BACKGROUND: Hepatic disorders are often associated with changes in the concentration of phosphorus‐31 ((31)P) metabolites. Absolute quantification offers a way to assess those metabolites directly but introduces obstacles, especially at higher field strengths (B(0) ≥ 7T). PURPOSE: To introduce a feasible method for in vivo absolute quantification of hepatic (31)P metabolites and assess its clinical value by probing differences related to volunteers' age and body mass index (BMI). STUDY TYPE: Prospective cohort. SUBJECTS/PHANTOMS: Four healthy volunteers included in the reproducibility study and 19 healthy subjects arranged into three subgroups according to BMI and age. Phantoms containing (31)P solution for correction and validation. FIELD STRENGTH/SEQUENCE: Phase‐encoded 3D pulse‐acquire chemical shift imaging for (31)P and single‐volume (1)H spectroscopy to assess the hepatocellular lipid content at 7T. ASSESSMENT: A phantom replacement method was used. Spectra located in the liver with sufficient signal‐to‐noise ratio and no contamination from muscle tissue, were used to calculate following metabolite concentrations: adenosine triphosphates (γ‐ and α‐ATP); glycerophosphocholine (GPC); glycerophosphoethanolamine (GPE); inorganic phosphate (P(i)); phosphocholine (PC); phosphoethanolamine (PE); uridine diphosphate‐glucose (UDPG); nicotinamide adenine dinucleotide‐phosphate (NADH); and phosphatidylcholine (PtdC). Correction for hepatic lipid volume fraction (HLVF) was performed. STATISTICAL TESTS: Differences assessed by analysis of variance with Bonferroni correction for multiple comparison and with a Student's t‐test when appropriate. RESULTS: The concentrations for the young lean group corrected for HLVF were 2.56 ± 0.10 mM for γ‐ATP (mean ± standard deviation), α‐ATP: 2.42 ± 0.15 mM, GPC: 3.31 ± 0.27 mM, GPE: 3.38 ± 0.87 mM, P(i): 1.42 ± 0.20 mM, PC: 1.47 ± 0.24 mM, PE: 1.61 ± 0.20 mM, UDPG: 0.74 ± 0.17 mM, NADH: 1.21 ± 0.38 mM, and PtdC: 0.43 ± 0.10 mM. Differences found in ATP levels between lean and overweight volunteers vanished after HLVF correction. DATA CONCLUSION: Exploiting the excellent spectral resolution at 7T and using the phantom replacement method, we were able to quantify up to 10 (31)P‐containing hepatic metabolites. The combination of (31)P magnetic resonance spectroscopy imaging data acquisition and HLVF correction was not able to show a possible dependence of (31)P metabolite concentrations on BMI or age, in the small healthy population used in this study. Level of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:597–607.