Characterization of the peak at 2.06ppm in 31P magnetic resonance spectroscopy of human liver: phosphoenolpyruvate or phosphatidylcholine?

• Published in: NMR in biomedicine 2015-07, Vol.28 (7), p.898
• Main Authors: Bierwagen, Alessandra, Begovatz, Paul, Nowotny, Peter, Markgraf, Daniel, Nowotny, Bettina, Koliaki, Chrysi, Giani, Guido, Kluppelholz, Birgit, Lundbom, Jesper, Roden, Michael
• Format: Article
• Language: English
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.3323

High field MR scanners can resolve a metabolite resonating at 2.06ppm in the in vivo proton-decoupled liver 31P MR spectrum. Traditionally this peak has been assigned to phosphoenolpyruvate (PEP), the key metabolite for gluconeogenesis. However, recent evidence supported the assignment to biliary phosphatidylcholine (PtdCh), which is produced in the liver and stored in the gall bladder. To elucidate the respective contributions of PtdCh and PEP to the in vivo resonance at 2.06ppm (PEP-PtdCh), we made phantom measurements that confirmed that both biliary PtdCh and PEP resonate approximately at 2ppm. The absolute quantification of PEP-PtdCh yielded concentrations ranging from 0.6 to 2.0mmol/l, with mean coefficients of variation of 4.8% for intraday and 7.2% for interday reproducibility in healthy volunteers. The T1 relaxation time of PEP-PtdCh was 0.97±0.30s in the liver and 0.44±0.11s in the gallbladder. Ingestion of a mixed meal decreased the concentration of PtdCh-PEP by approximately 12%. In the retrospective analysis, PEP-PtdCh was 68% higher in the liver of subjects with gallbladder infiltration of the volume of interest (VOI) compared with those without gallbladder infiltration. PEP-PtdCh was also significantly higher in the liver of cholecystectomy patients compared with volunteers without gallbladder infiltration, which suggests increased intrahepatic bile fluid as a compensation for gall bladder removal. These results show that liver PtdCh is the major component of the resonance at 2.06ppm and that careful VOI positioning is mandatory to avoid interference from the gallbladder. Copyright © 2015 John Wiley & Sons, Ltd.