IMAGING OF (H2O)-O-17 DISTRIBUTION IN THE BRAIN OF A LIVE RAT BY USING PROTON-DETECTED O-17 MRI

Imaging of (H2O)-O-17 has a number of important applications. Mapping the distribution of (H2O)-O-17 produced by oxidative metabolism of O-1 7-enriched oxygen gas may lead to a new method of metabolic functional imaging; regional cerebral blood flow also can be measured by measuri ng the (H2O)-O-17 distribution after the injection of O-17-enriched ph ysiological saline solution. Previous studies have proposed a method f or indirect detection of O-17. The method is based on the shortening o f the proton T-2 in (H2O)-O-17 solutions, caused by the residual O-17- H-1 scalar coupling and transferred to the bulk water via fast chemica l exchange. It has been shown that the proton T-2 of (H2O)-O-17 soluti ons can be restored to that of (H2O)-O-16 by irradiating the resonance frequency of the O-17 nucleus. The indirect O-17 image thus is obtain ed by taking the difference between two T-2-weighted spin-echo images: one acquired after irradiation of the O-17 resonance and one acquired without irradiation, It also has been established that, at relatively low concentrations of (H2O)-O-17, the indirect method yields an image that quantitatively reflects the (H2O)-O-17 distribution in the sampl e. The method is referred to as PRIMO (proton imaging of oxygen). In t his work, we show in vivo proton images of the (H2O)-O-17 distribution in a rat brain after an i.v. injection of (H2O)-O-17 enriched physiol ogical saline solution. Implementing the indirect detection method in an echo-planar imaging sequence enabled obtaining (H2O)-O-17 images wi th good spatial and temporal resolution of few seconds.