Quantitative T1ρ NMR Spectroscopy of Rat Cerebral Metabolites in Vivo: Effects of Global Ischemia

Abstract

The NMR relaxation times (T1ρ, T2, and T 1) of water, N-acetylaspartate (NAA), creatine (Cr), choline-containing compounds (Cho), and lactate (Lac) were quantified in rat brain at 4.7 T. In control animals, the cerebral T1ρ figures, as determined with a spin-lock field of 1.0 G, were 575 ± 30 ms, 380 ± 19 ms, 705 ± 53 ms, and 90 ± 1 ms for NAA, Cr, Cho, and water, respectively. The T1ρ figures were 62-103% longer than their respective T2 values determined by a multiecho method. In global (ischemic) ischemia, T1ρ of NAA declined by 34%, that of Cr and Cho did not change, and that of water increased by 10%. The T 1ρ of lactate in ischemic brain was 367 ± 44 ms. Similar patterns of changes were observed in the multiecho T2 of these cerebral metabolites. The T1 of water and NAA changed in a fashion similar to that of T1ρ and T2. These results show differential responses in metabolite and water T1ρ relaxation times following ischemia, and indicate that metabolite T1ρ and T2 relaxation times behave similarly in the ischemic brain. The contributions of dipolar and nondipolar effects on T1ρ relaxation in vivo are discussed in this work. © 2004 Wiley-Liss, Inc.