Reproducibility of absolute quantification of adenosine triphosphate and inorganic phosphate in the liver with localized 31 P-magnetic resonance spectroscopy at 3-T using different coils

Concentrations of the key metabolites of hepatic energy metabolism, adenosine triphosphate (ATP) and inorganic phosphate (P _i), can be altered in metabolic disorders such as diabetes mellitus. ³¹Phosphorus ( ³¹P)-magnetic resonance spectroscopy (MRS) is used to noninvasively measure hepatic metabolites, but measuring their absolute molar concentrations remains challenging. This study employed a ³¹P-MRS method based on the phantom replacement technique for quantifying hepatic ³¹P-metabolites on a 3-T clinical scanner. Two surface coils with different size and geometry were used to check for consistency in terms of repeatability and reproducibility and absolute concentrations of metabolites. Day-to-day (n = 8) and intra-day (n = 6) reproducibility was tested in healthy volunteers. In the day-to-day study, mean absolute concentrations of γ-ATP and P _i were 2.32 ± 0.24 and 1.73 ± 0.26 mM (coefficient of variation [CV]: 7.3% and 8.8%) for the single loop, and 2.32 ± 0.42 and 1.73 ± 0.27 mM (CVs 6.7% and 10.6%) for the quadrature coil, respectively. The intra-day study reproducibility using the quadrature coil yielded CVs of 4.7% and 6.8% for γ-ATP and P _i without repositioning, and 6.3% and 7.1% with full repositioning of the volunteer. The results of the day-to-day data did not differ between coils and visits. Both coils robustly yielded similar results for absolute concentrations of hepatic ³¹P-metabolites. The current method, applied with two different surface coils, can be readily utilized in long-term and interventional studies. In comparison with the single loop coil, the quadrature coil also allows measurements at a greater distance between the coil and liver, which is relevant for studying people with obesity.