Reproducibility of 3D MRSI for imaging human brain glucose metabolism using direct ( (2) H) and indirect ( (1) H) detection of deuterium labeled compounds at 7T and clinical 3T

IntroductionDeuterium metabolic imaging (DMI) and quantitative exchange label turnover (QELT) are novel MR spectroscopy techniques for non-invasive imaging of human brain glucose and neurotransmitter metabolism with high clinical potential. Following oral or intravenous administration of non-ionizing [6,6’-2H2]-glucose, its uptake and synthesis of downstream metabolites can be mapped via direct or indirect detection of deuterium resonances using2H MRSI (DMI) and1H MRSI (QELT), respectively.The purpose of this study was to compare the dynamics of spatially resolved brain glucose metabolism, i.e., estimated concentration enrichment of deuterium labeled Glx (glutamate+glutamine) and Glc (glucose) acquired repeatedly in the same cohort of subjects using DMI at 7T and QELT at clinical 3T.MethodsFive volunteers (4m/1f) were scanned in repeated sessions for 60 min after overnight fasting and 0.8g/kg oral [6,6’-2H2]-glucose administration using time-resolved 3D2H FID-MRSI with elliptical phase encoding at 7T and 3D1H FID-MRSI with a non-Cartesian concentric ring trajectory readout at clinical 3T.ResultsOne hour after oral tracer administration regionally averaged deuterium labeled Glx4concentrations and the dynamics were not significantly different over all participants between 7T2H DMI and 3T1H QELT data for GM (1.29±0.15 vs. 1.38±0.26 mM, p=0.65 & 21±3 vs. 26±3 µM/min, p=0.22) and WM (1.10±0.13 vs. 0.91±0.24 mM, p=0.34 & 19±2 vs. 17±3 µM/min, p=0.48). Also, the observed time constants of dynamic Glc6data in GM (24±14 vs. 19±7 min, p=0.65) and WM (28±19 vs. 18±9 min, p=0.43) dominated regions showed no significant differences.Between individual2H and1H data points a weak to moderate negative correlation was observed for Glx4concentrations in GM (r=-0.52, p6data GM (r=- 0.61, pConclusionThis study demonstrates that indirect detection of deuterium labeled compounds using1H QELT MRSI at widely available clinical 3T without additional hardware is able to reproduce absolute concentration estimates of downstream glucose metabolites and the dynamics of glucose uptake compared to2H DMI data acquired at 7T. This suggests significant potential for widespread application in clinical settings especially in environments with limited access to ultra-high field scanners and dedicated RF hardware.