Noninvasive quantification of human brain ascorbate concentration using¹H NMR spectroscopy at 7 T

Ascorbate (Asc, vitamin C) was quantified in the human brain noninvasively using two different 1H NMR spectroscopy methods: short-echo time STEAM and MEGA-PRESS homonuclear editing. Taking advantage of increased sensitivity and chemical shift dispersion at 7 T, Asc was quantified with increased reliability relative to our previous study accomplished at 4 T. Asc concentration quantified from short-echo time spectra measured from the occipital lobe of eight healthy subjects ([Asc]=1.1 ± 0.3mmol/g, meanWSD) was in excellent agreement with Asc concentration quantified from the same volume of interest using homonuclear editing ([Asc]=1.2 ± 0.2μmol/g). This agreement indicates that at 7 T, Asc can be reliably quantified in the human brain simultaneously with 15 other metabolites. Additional advantages of the short-echo time approach were: shorter measurement time than homonuclear editing and minimal effect of T ₂ relaxation on Asc quantification. High magnetic field was also beneficial for Asc quantification with MEGA-PRESS because increased chemical shift dispersion enabled editing with full efficiency, which resulted in a supra-linear gain in signal-to-noise ratio relative to 4 T.