(a) Left Panel: 2D J -resolved 1
H-MR spectrum recorded from the voxel shown in figure 2b. Only the large singlet resonances are labeled at F1 = 0 Hz although information from J-coupled metabolites is spread over the 2D surface. The 2D spectrum is presented in magnitude mode for presentation purposes, and is characterized by two orthogonal frequency axes: chemical shift (F2) and J-coupling (F1) dimensions. Exponential apodization was applied along F2 (line broadening = 3 Hz) whereas a sinebell-squared apodization filter (30° phase-shifted) was applied along the F1 axis. The chemical shift axis has been expanded to show the 0.6 – 4.4 ppm region whereas the full J-coupling dimension (± 50 Hz) is presented. The dominating singlet resonances corresponding to the NAA, total Cr and total Cho methyl groups are labeled and reside perpendicular to F1 = 0 Hz (solid black line) at 2.0, 3.0 and 3.2 ppm, respectively. Lipid signals that probably arise due to chemical shift displacement are identified at and around 1.4 ppm (F1 = 0 Hz) and the total Cr methylene resonance is observed at 3.9 ppm. (b) Right Panel: LCModel analysis of a single row extracted from F1 = 0 Hz. The raw data, LCModel fit, residual and individual metabolite fits are displayed. It is important to note that the 1D 1H-MR spectrum is real data, which is the data type required for LCModel analysis. The LCModel fit (solid red line) for the F1 = 0 Hz extraction is overlaid on the raw data and the residual (LCModel fit minus raw data) is displayed at the top of the figure. The residual is free from large subtraction artifacts and clearly illustrates the high-quality spectral fit achieved using the described quantification methods. Data extracted from the center of the F1 dimension in this manner is entirely equivalent to signal averaging all 24 TE steps, a procedure often referred to as TE-averaging. TE-averaged 1H-MRS spectra typically show the large singlet methyl (CH3) resonances of NAA, total Cr and total Cho with significant attenuation of resonances J-coupled metabolite species. (see text for more details).