Use of magnetic resonance imaging for in vivo measurements of water content in human brain: method and normal values

Object. The authors present a quantitative in vivo magnetic resonance (MR) imaging method and propose its use for the accurate assessment of brain water in humans. Methods. With this technique, a pure T-1-weighted image of a selected brain slice in a patient is generated, and the image is subsequently converted to a pure water image by means of an equation derived from a tissue relaxation model. The image intensity in the resulting water map directly yields absolute measures of water expressed in grams of water per gram of tissue at a given anatomical location. The method has been validated previously in a series of phantom experiments and in an infusion model of brain edema in cats. In this report, the authors evaluate the method by using samples of tissue harvested from patients who underwent surgery for brain tumor removal and apply the technique to a series of normal volunteers, providing average regional brain water content (f(w)) values for a range of tissues. Application of the method in pathological conditions such as head trauma, tumor, and hydrocephalus allows quantification of regional or global increases in f(w) that result from edema. Conclusions. It is now possible to obtain accurate brain water measurements with the anatomical resolution of MR imaging. This permits monitoring of the development and resolution of edema in a variety of clinical circumstances, thus enhancing understanding of the underlying pathophysiological processes.