Enhancing Fraction in Glioma and Its Relationship to the Tumoral Vascular Microenvironment: A Dynamic Contrast-Enhanced MR Imaging Study

BACKGROUND AND PURPOSE: EnF is a newly described measure of proportional tumor enhancement derived from DCE-MR imaging. The aim of this study was to assess the relationship between EnF and the more established DCE-MR imaging parameters: K-trans, v(e), and v(p). MATERIALS AND METHODS: Forty-two patients with 43 gliomas (16 grade II, 3 grade III, and 24 grade IV) were studied. Imaging included pre- and postcontrast T1-weighted sequences through the lesion and T1-weighted DCE-MR imaging. Parametric maps of EnF, K-trans, v(e), and v(p) were generated. Voxels were classified as enhancing if the IAUC was positive (EnF(IAUC60>0)). A threshold of IAUC > 2.5 mmol.s was used to generate EnF(IAUC60>2.5). Both measures of EnF were compared with the DCE-MR imaging parameters (K-trans, v(e), and v(p)). RESULTS: In grade II gliomas, EnF(IAUC60>0) and EnF(IAUC60>2.5) correlated with v(p) (R-2 = 0.6245, P < .0005; and R-2 = 0.4727, P = .003) but not with K-trans or v(e). In grade IV tumors, both EnF(IAUC60>0) and EnF(IAUC60>2.5) correlated with K-trans (R-2 = 0.3501, P = .001; and R-2 = 0.4699, P < .0005) and v(p) (R = 0.1564, P = .01; and R-2 = 0.2429, P = .007), but not with v(e). Multiple regression analysis showed as the only independent correlate of both EnF(IAUC60>0) and EnF(IAUC60>2.5) for grade IV tumors. CONCLUSIONS: This study suggests that in grade II tumors, EnF reflects v(p) and varies due to changes in vascular density. In grade IV gliomas, EnF is affected by K-trans with secondary associated changes in v(p).