Abstract
Vessel size imaging (VSI) for brain tumor characterization was evaluated and the vessel size index measured by MRI (VSI~MRI~) was correlated with VSI obtained by histology (VSI~histo~). Blood volume (BV) and VSI maps were obtained on 12 rats by simultaneous measurements of R~2~* and R~2~, before and after the injection of a macromolecular contrast agent, AMI‐227. Immunostaining of collagen IV in vessels was performed. An expression was derived for evaluating VSI from stereologic measurements on histology data (VSI~histo~). On BV and VSI images obtained from large‐size tumors (n = 9), three regions could be distinguished and correlated well with histological sections: a high BV region surrounding the tumor, a necrotic area where BV is very low, and a viable tumor tissue region showing lower BV but higher VSI than the normal rat cortex, with the presence of larger vessels. The quantitative analysis showed a good correlation (Spearman rank's rho = 0.74) between VSI~histo~ and VSI~MRI~ with a linear regression coefficient of 1.17. The good correlation coefficient supports VSI imaging as a quantitative method for tumor vasculature characterization. Magn Reson Med 51:533–541, 2004. © 2004 Wiley‐Liss, Inc.