COMPARISON OF CALIBRATION STRATEGIES FOR THE IN-VIVO DETERMINATION OF ABSOLUTE METABOLITE CONCENTRATIONS IN THE HUMAN BRAIN BY P-31 MRS

Cerebral concentrations of phosphorus metabolites can be assessed non-invasively by P-31 MRS provided the metabolite signals are calibrated with the signal of a standard of known concentration. The reliability of the concentration estimates depends mainly on the strategy of calibration. Three strategies were compared by assessing the concentrations both in a test dummy and in the brain of volunteers. The first strategy utilized tissue water as an internal heteronuclear concentration standard. The second and third strategies used a phosphorus solution as an external homonuclear standard; this solution was either put into a reference bottle placed on top of the head or into a simulation phantom measured instead of the head. Localization was always achieved with the ISIS pulse sequence. The two external homonuclear strategies achieved a higher accuracy (mean error approximate to 5%,) and reproducibility (mean SD approximate to 8%) of the concentration estimates than the internal heteronuclear strategy (mean error approximate to 11%; mean SD approximate to 15%).