Abstract
^17^O 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 Β± 0.08 ms, T = 1.79 Β± 0.04 ms, and T~1~ = 4.47 Β± 0.14 ms at 4.7T (N = 5); T~2~ = 3.03 Β± 0.09 ms, T = 1.80 Β± 0.06 ms, and T~1~ = 4.84 Β± 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 signalβtoβnoise ratio (SNR) within 15 s of data acquisition despite the relatively low gyromagnetic ratio of this nucleus. Such a 15βs 2D ^17^OβMRS imaging data set obtained for natural abundance H~2~^17^O in the rat brain yielded an SNR greater than 40:1 for a βΌ16ΞΌl 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^OβMRS 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 45:543β549, 2001. Β© 2001 WileyβLiss, Inc.