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 H217O in the rat brain at 4.7 and 9.4 Tesla. The relaxation times were found to be magnetic field independent (T2 = 3.03 ± 0.08 ms, T  *2 = 1.79 ± 0.04 ms, and T1 = 4.47 ± 0.14 ms at 4.7T (N = 5); T2 = 3.03 ± 0.09 ms, T  *2 = 1.80 ± 0.06 ms, and T1 = 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 17O 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 17O 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 17O‐MRS imaging data set obtained for natural abundance H217O in the rat brain yielded an SNR greater than 40:1 for a ∼16μl voxel. This approach was employed to measure cerebral blood flow using a bolus injection of H217O via one internal carotid artery. These results demonstrate the ability of 17O‐MRS imaging to reliably map the H217O 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. © 2001 Wiley‐Liss, Inc.