Fig. 4

Repeatability effects of normalization. Deuterium metabolic imaging was normalized to either a baseline examination acquired before ²H-glucose administration, to the cerebellum in the same examination, or to external phantoms (a). Normalization to the baseline allows absolute quantification of apparent metabolite concentrations but requires two examinations. In principle, normalization to external phantoms does the same in a single examination. Internal normalization to the cerebellum is does not give metabolite concentrations. The whole-brain within- and between-subject coefficients of variation (CoV) were lowest with internal normalization to the cerebellum, while normalization to a baseline scan or external phantoms yielded higher variation (b, c). Glx Glutamate + glutamine