Finally, what does a 1H-MRS precisely measure?

Dear MRS experts,

I already asked some of you (@PGMM, @admin, …), but with no consensus explanation: What is exactly done during H-MRS quantification? I mean do we quantify only the free metabolites (or unbound) or the free metabolites + the metabolite in complex with them receptors (bound metabolites)?

Thank you,

Frederic