O-17 relaxation time and NMR sensitivity of cerebral water and their fielddependence

O-17 spin relaxation times and sensitivity of detection were measured for n atural abundance (H2O)-O-17 in the rat brain at 4.7 and 9.4 Tesla, The rela xation 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 m s at 9.4T (N = 5)), consistent with the concept that the dominant relaxatio n mechanism is the quadrupolar interaction for this nucleus. The O-17 NMR s ensitivity 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 w as possible to obtain localized O-17 spectra with an excellent signal-to-no ise ratio (SNR) within 15 s of data acquisition despite the relatively low gyromagnetic ratio of this nucleus. Such a 15-s 2D O-17-MRS imaging data se t obtained for natural abundance (H2O)-O-17 in the rat brain yielded an SNR greater than 40:1 for a similar to 16 mul voxel, This approach was employe d to measure cerebral blood flow using a bolus injection of (H2O)-O-17 via one internal carotid artery. These results demonstrate the ability of O-17- MRS imaging to reliably map the (H2O)-O-17 dynamics in the brain tissue, an d its potential for determining tissue blood flow end oxygen consumption ra te changes in vivo. Magn Reson Med 45:543649, 2001, (C) 2001 Wiley-Liss, In c.