We are using Osprey to analyze our PRESS data (Siemens 3T), and my PI has questions about the quantification/tissue correction that I would appreciate some help with:
More or less I understand how the correction is done for CSF, because CSF does not have any metabolites, but if we correct for GM and WM fractions we assume that:
a) concentrations of metabolites is different in GM and WM especially for NAA - this is true, but I do not know what is the magnitude of this differences (i.e. 20-50% more/less) and what coefficient Osprey is using for this.
b) this difference is stable and not affected by other factors (i.e. age) or changes simultaneously - i.e. creatine is increasing in both WM and GM. Would we need to collect data from a second MRS voxel in WM?
c) where in the Matlab code is the calculation of the metabolite concentration (NAc, Ch, or Cr) and/or the normalized GM fraction (fGM_vol / (fGM_vol fWM_vol)) as they described in Gasparovic?