Sensitivity of USPIO-enhanced R2 imaging to dynamic blood volume changes in the rat kidney

Abstract

Purpose: To determine whether MRI in combination with an intravascular contrast agent is sensitive to pharmacologically induced vasodilation and vasoconstriction in the rat kidney. Materials and Methods: R2 imaging was performed in 25 Sprague Dawley rats at 3 Tesla in the presence of ferumoxytol, an ultrasmall superparamagnetic iron oxide (USPIO) agent with a long plasma half-life. R2 changes were measured following manipulation of blood volume by intravenous administration of adenosine, a short-acting vasodilator, or NG-nitro-L-arginine methyl ester (L-NAME), a long-acting nitric oxide synthase inhibitor with known vasoconstrictive effects. As a control, R2 responses to adenosine and L-NAME were also examined in the absence of ferumoxytol. Results: In the presence of ferumoxytol, adenosine induced a significant increase in R 2, while L-NAME produced a reduction, although the latter was not statistically significant. Control experiments revealed small R2 changes in the absence of ferumoxytol. An incidental finding was that the cross-sectional area of the kidney also varied dynamically with adenosine and L-NAME. Conclusion: Our results suggest that ferumoxytol-enhanced R2 imaging is sensitive to adenosine-induced vasodilation. The responses to L-NAME, however, were not statistically significant. The variations in kidney size and the R2 changes in the absence of ferumoxytol may reflect alterations in the volume of the renal tubules. Copyright © 2011 Wiley-Liss, Inc.