title: Lithium compartmentation in brain by 7Li MRS: effect of total lithium concentration.
abstract: In previous work at 4.7 T, the individual components of biexponential (7) Li transverse (T2 ) spin relaxation in rat brain in vivo were tentatively identified with intra- and extracellular Li. The goal in this work was to estimate Li's compartmental distribution as a function of total Li concentration in brain from the biexponential decays. Here a localized, biexponential (7) Li T2 MR spin-relaxation study with isotopically enriched (7) LiCl is reported in rat brain in vivo at 7 T. Additionally, a simple linear interpolation using the biexponential T2 values to estimate intracellular Li from individual monoexponential T2 decays was assessed. Intracellular T2 was 14.8 ± 4.3 ms and extracellular T2 was 295 ± 61 ms. The fraction of intracellular brain Li ranged from 37.3 to 64.8% (mean 54.5 ± 6.7%) and did not correlate with total Li concentration. The estimated intracellular Li concentration ranged from 47 to 80% (mean 68.3 ± 8.5%) of the total brain Li concentration and was highly correlated with it. The monoexponential estimates of the intracellular-Li fractions and derived concentrations averaged about 15% higher than the corresponding biexponential estimates. This work supports the previous conclusion that a large fraction of Li in the brain is within the intracellular compartment.
authors: Center for Imaging Research, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0583, USA. richard.komoroski@uc.edu
authors: Richard A
authors: RA
authors: Komoroski
authors: Diana M
authors: DM
authors: Lindquist
authors: John M
authors: JM
authors: Pearce
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D008094:Lithium / Q000032:analysis / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D011522:Protons; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D011522:Protons; D008094:Lithium
keywords: biexponential relaxation; bipolar disorder; rat brain; spin-spin relaxation time; transverse relaxation time
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