Chromium(VI) as a novel MRI contrast agent for cerebral white matter: preliminary results in mouse brain in vivo.

This work demonstrates that intraventricular microinjections of a low dose of potassium dichromate (0.4 microL of 10 mM solution) yield a specific contrast enhancement of white matter (WM) tracts in T1-weighted 3D MRI of mouse brain in vivo. Pronounced and persistent signal increases (40-100% at 24 hr after injection) were observed in the corpus callosum, anterior commissure, fornix, and stria medullaris, as well as in the mammillothalamic tract and fasciculus retroflexus. These results suggest that the extracellular diffusion of diamagnetic chromium(VI) (Cr(VI)) after injection is followed by a tissue-specific reduction to paramagnetic Cr(V) and (III), which relies predominantly on the oxidation of myelin lipids. Because Cr(VI)-induced contrast leads to only a mild unspecific enhancement (10-20%) of gray matter (GM) structures, such as the hippocampal formation, the method reveals novel information that differs from that obtainable using other paramagnetic ions, such as manganese.