Quantitative T1rho NMR spectroscopy of rat cerebral metabolites in vivo: effects of global ischemia.

The NMR relaxation times (T(1rho), T(2), 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 T(1rho) 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 T(1rho) figures were 62-103% longer than their respective T(2) values determined by a multiecho method. In global (ischemic) ischemia, T(1rho) of NAA declined by 34%, that of Cr and Cho did not change, and that of water increased by 10%. The T(1rho) of lactate in ischemic brain was 367 +/- 44 ms. Similar patterns of changes were observed in the multiecho T(2) of these cerebral metabolites. The T(1) of water and NAA changed in a fashion similar to that of T(1rho) and T(2). These results show differential responses in metabolite and water T(1rho) relaxation times following ischemia, and indicate that metabolite T(1rho) and T(2) relaxation times behave similarly in the ischemic brain. The contributions of dipolar and nondipolar effects on T(1rho) relaxation in vivo are discussed in this work. Copyright 2004 Wiley-Liss, Inc.