MRI assessment of microvascular characteristics in experimental breast tumors using a new blood pool contrast agent (MS-325) with correlations to histopathology.

A new contrast medium, MS-325, was compared to albumin-(Gd-DTPA)(30) in 18 chemically induced rat breast tumors based on quantitative estimates of microvascular permeability (K(PS)) and fractional plasma volume (fPV) using a two-compartment bidirectional model. No significant correlation was found between MS-325-enhanced microvascular assays with either tumor grade or with microvascular counts (MVCs). In comparison, the correlation coefficient between K(PS) and histologic tumor grade using albumin-(Gd-DTPA)(30) (r =.58) was statistically significant (P <.01). Also, using albumin-(Gd-DTPA)(30), a significant correlation (r =.55, P <.05) was observed between the K(PS) and MVC, a biomarker of angiogenesis. Correlations between fPV and MVC were not statistically significant for either contrast medium. In conclusion, using MS-325, no significant correlations between the MR-estimated permeability values or plasma volumes were observed in experimental breast tumors with either the histologic tumor grade or MVC. This analysis confirms our previous determination that capillary permeability estimates, using a prototype large molecular contrast medium, albumin-(Gd-DTPA)(30), correlate significantly with both histologic tumor grade and MVC. Copyright 2001 Wiley-Liss, Inc.