In vivo characterization of the downfield part of 1 H MR spectra of human brain at 9.4 T: Magnetization exchange with water and relation to conventionally determined metabolite content

Nicole D. Fichtner, Ioannis-Angelos Giapitzakis, Nikolai Avdievich, Ralf Mekle, Daniel Zaldivar, Anke Henning, Roland Kreis
2017 Magnetic Resonance in Medicine  
Purpose: To perform exchange-rate measurements on the in vivo human brain downfield spectrum (5-10ppm) at 9.4T and to compare the variation in concentrations of the downfield resonances and of known upfield metabolites to determine potential peak labels. Methods: Non-water suppressed metabolite cycling was used in combination with an inversion transfer technique in two brain locations in healthy volunteers to measure the exchange rates and T 1 values of exchanging peaks. Spectra were fitted
more » ... a heuristic model of a series of 13 or 14 Voigt lines, and a Bloch-McConnell model was used to fit exchange rate curves. Concentrations from non-water inverted spectra upfield and downfield were compared. Results: Mean T 1 values ranged from 0.40 to 0.77 s and exchange rates from 0.74 to 13.8 s -1 . There were no significant correlations between downfield and upfield concentrations, except for NAA, with a correlation coefficient of 0.63 and p<0.01. Conclusions: Using ultra-high field allowed improved separation of peaks in the 8.2-8.5ppm amide proton region, and the exchange rates of multiple downfield resonances including the 5.8ppm peak, previously tentatively assigned to urea, were measured in vivo in human brain. Downfield peaks are comprised of overlapping components, and largely missing correlations between upfield and downfield resonances -though not conclusive -indicate limited contributions from metabolites present upfield to the downfield spectrum. Figure S2 : Scatter plots for the range of correlations tested between upfield and downfield peak areas. Occipital ROI data points shown in blue, WM ROI data points shown in red. The downfield peaks are along the x-axes, and the upfield peaks along the y-axes, as labeled in the figure. Supporting
doi:10.1002/mrm.26968 pmid:29034505 fatcat:lunxi4kobrhb5fxvp5jw3dhoiu