Imaging of H(2)(17)O distribution in the brain of a live rat by using proton-detected (17)O MRI

Imaging of H(2)(17)O has a number of important applications. Mapping the distribution of H(2)(17)O produced by oxidative metabolism of (17)O-enriched oxygen gas may lead to a new method of metabolic functional imaging; regional cerebral blood flow also can be measured by measuring the H(2)(17)O distribution after the injection of (17)O-enriched physiological saline solution. Previous studies have proposed a method for indirect detection of (17)O. The method is based on the shortening of the proton T(2) in H(2)(17)O solutions, caused by the residual (17)O-(1)H scalar coupling and transferred to the bulk water via fast chemical exchange. It has been shown that the proton T(2) of H(2)(17)O solutions can be restored to that of H(2)(16)O by irradiating the resonance frequency of the (17)O nucleus. The indirect (17)O image thus is obtained by taking the difference between two T(2)-weighted spin-echo images: one acquired after irradiation of the (17)O resonance and one acquired without irradiation. It also has been established that, at relatively low concentrations of H(2)(17)O, the indirect method yields an image that quantitatively reflects the H(2)(17)O distribution in the sample. The method is referred to as PRIMO (proton imaging of oxygen). In this work, we show in vivo proton images of the H(2)(17)O distribution in a rat brain after an i.v. injection of H(2)(17)O-enriched physiological saline solution. Implementing the indirect detection method in an echo-planar imaging sequence enabled obtaining H(2)(17)O images with good spatial and temporal resolution of few seconds.