Lithium visibility in rat brain and muscle in vivo by 7Li NMR imaging

The apparent concentration of lithium (Li) in vivo was determined for several regions in the brain and muscle of rats by Li-7 NMR imaging at 4.7 T with inclusion of an external standard of known concentration and visibility. The average apparent concentrations were 10.1 mM for muscle, and 4.2-5.3 mM for various brain regions under the dosing conditions used. The results were compared to concentrations determined in vitro by high-resolution Li-7 NMR spectroscopy of extracts of brain and muscle tissue from the same rats. The comparison provided estimates of the Li-7 NMR visibility of the Li cation in each tissue region. Although there was considerable scatter of the calculated visibilities among the five rats studied, the results suggested essentially full visibility (96%) for Li in muscle, and somewhat reduced visibility (74-93%) in the various brain regions. (C) 1998 Academic Press.