Measurements of transient contrast enhancement by localized water NMR spectroscopy

It is shown that a localized spectroscopic method can be used to detect transient contrast enhancement of transverse relaxation and to measure cerebral blood volume. High-resolution spectra of the water resonance were recorded from small-volume elements of the brain following bolus administration of contrast agents. The integrated signal corresponds to the intensity that would be portrayed in a single voxel in an MR image. The spectral data can be analyzed to more precisely describe the alterations in tissue NMR signal incurred by the agent than is possible by simple image intensity measurement. In particular, the contributions to relaxation by diffusion of water molecules and static line broadening in the field inhomogeneities generated by intravascular contrast agents can be separately evaluated from the spectral analysis. The method has been used to study rat brain before and during bolus injections of contrast agents, and used to compare the differential effects of two different agents, viz., Gd-DTPA, and Dy-DTPA. While the integrated intensity change produced by Dy-DTPA was approximately 35% greater than that for Gd-DTPA, the corresponding linewidths differed by over 300%. This method may also provide measurements of changes in tissue oxygenation with high signal-to-noise ratios in brain activation studies.