17O relaxation time and NMR sensitivity of cerebral water and their field dependence.

17O spin relaxation times and sensitivity of detection were measured for natural abundance H(2)(17)O in the rat brain at 4.7 and 9.4 Tesla. The relaxation times were found to be magnetic field independent (T(2) = 3.03 +/- 0.08 ms, T(*)(2) = 1.79 +/- 0.04 ms, and T(1) = 4.47 +/- 0.14 ms at 4.7T (N = 5); T(2) = 3.03 +/- 0.09 ms, T(*)(2) = 1.80 +/- 0.06 ms, and T(1) = 4.84 +/- 0.18 ms at 9.4T (N = 5)), consistent with the concept that the dominant relaxation mechanism is the quadrupolar interaction for this nucleus. The (17)O NMR sensitivity was more than fourfold higher at 9.4T than at 4.7T, for both the rat brain and a sodium chloride solution. With this sensitivity gain, it was possible to obtain localized (17)O spectra with an excellent signal-to-noise ratio (SNR) within 15 s of data acquisition despite the relatively low gyromagnetic ratio of this nucleus. Such a 15-s 2D (17)O-MRS imaging data set obtained for natural abundance H(2)(17)O in the rat brain yielded an SNR greater than 40:1 for a approximately 16 microl voxel. This approach was employed to measure cerebral blood flow using a bolus injection of H(2)(17)O via one internal carotid artery. These results demonstrate the ability of (17)O-MRS imaging to reliably map the H(2)(17)O dynamics in the brain tissue, and its potential for determining tissue blood flow and oxygen consumption rate changes in vivo. Magn Reson Med 45:543-549, 2001. Copyright 2001 Wiley-Liss, Inc.