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

Abstract

High field MR scanners can resolve a metabolite resonating at 2.06 ppm in the in vivo proton-decoupled liver (31) P 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 2.06 ppm (PEP-PtdCh), we made phantom measurements that confirmed that both biliary PtdCh and PEP resonate approximately at 2 ppm. The absolute quantification of PEP-PtdCh yielded concentrations ranging from 0.6 to 2.0 mmol/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 ± 0.30 s in the liver and 0.44 ± 0.11 s 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 2.06 ppm and that careful VOI positioning is mandatory to avoid interference from the gallbladder.

In-vivo 31P-MRS of skeletal muscle and liver: A way for non-invasive assessment of their metabolism

“…To avoid possible contamination from muscle tissue, gall bladder, or adjacent liver tissue, localization of the hepatic 31 P-MRS signal must be achieved [8], [17], [53], [217]. To this end, a variety of different strategies (Fig.…”

“…Increased fructose intake over a four week period was also shown to cause an increase in NADH in healthy volunteers [40]. Moreover, PtdC – a dominant component of the human bile MRS signal – contribution to the hepatic in vivo 31 P-MRS signal was identified [8] and independently confirmed [217]. Further studies should investigate the potential use of the PtdC resonance for metabolic studies of the liver, gallbladder, and bile ducts.…”

Phosphodiester content measured in human liver by in vivo 31P MR spectroscopy at 7 tesla

“…The PDE peak comprises signal from glycerophosphocholine (GPC), and glycerophosphoenthanolamine (GPE), cell membrane degradation products . Close to the PDE resonance, there is an overlap of signals from phosphoenolpyruvate (PEP) and, more importantly, from phosphatidylcholine (PtdC), which is a predominant phospholipid component of bile . At lower field strengths, the spectral resolution needed to individually resolve these five peaks is only possible with 1 H decoupling .…”

Non-Invasive Analysis of Human Liver Metabolism by Magnetic Resonance Spectroscopy

“…The challenges and potential limiting factors of high-field in vivo 31 P NMR MRS include design and implementation of RF hardware for optimal observation of hepatic metabolites, avoidance of confounding signals from non-hepatic tissues in intimate contact with the liver such as phosphatidylcholine from the gall-bladder and phosphcreatine from surrounding muscle [4,47,48]; and maintaining efficient 1 H-decoupling without exceeding the safe limits for tissue RF power deposition. Finally, there are hepatic studies that integrate the observation of 31 P and 1 H thereby providing correlated information of phospho-metabolites with other species such as lipids [49][50][51].…”