Metabolites explored in 1H-MRS

Only a limited number of molecules with protons are observable in MRS.

In brain MRS, the principle molecules that can be analyzed are (fig. 15.1):

• N-acetyl-asparate (NAA) (molecule present in healthy neurones) at 2.0 ppm
• Creatine/phosphocreatine (Cr) (energy metabolism molecules) at 3.0 ppm
• Choline compounds (Cho) (marker in the synthesis and breakdown of cell membranes) at 3.2 ppm
• Myo-inositol (mI) (only found in glial tissue) at 3.5 ppm (figure 15.2)
• Glutamine-Glutamate-GABA complex (Glx) (neurotransmitters) between 2.1 and 2.5 ppm
• Lactate (Lac) (anaerobic metabolism): doublet at 1.35 ppm (figure 15.3)
• Free lipids (Lip): wide resonance, doublet at 1.3 and 0.9 ppm

In prostatic MRS, the citrate peak is also looked for at 2.6 ppm.

The number of discernable metabolites will vary according to the TE of the spectroscopy sequence: the longer the TE (135 or 270 ms), the more long T2 metabolites are selected. With short TE (15 to 20 ms), the spectrum will be more complex because of the greater number of superimposed peaks, producing a number of problems for quantification and interpretation.