Dynamic in vivo oxymetry using Overhauser enhanced MR imaging

A noninvasive method for in vivo measurement of the oxygen concentration ha s been developed. By introducing a novel contrast medium (CM) based on a si ngle electron substance, it is possible to enhance the proton signal throug h the Overhauser effect. A low-field magnetic resonance scanner is used to image the proton nuclei of the object. The electron spin transition of the CM is saturated using rf irradiation. As a consequence, the nuclear polariz ation becomes enhanced through dipole-dipole interaction. The signal enhanc ement is a function of rf power and of the EPR line width of the substance, which is influenced by the oxygen concentration. The maximum in vivo enhan cement has been measured to 60. Image data, generated with different scanni ng parameters, is used in a postprocessing method to generate images showin g pO(2) and the contrast medium concentration, respectively. The mathematic al foundation of the postprocessing algorithm is outlined. The results from phantom experiments and animal experiments, in which the oxygen content of the inspired gas was varied, are presented. The potential for human imagin g is discussed. (C) 2000 Wiley-Liss, Inc.