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 (R² = 0.6245, P < .0005; and R² = 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 (R² = 0.3501, P = .001; and R² = 0.4699, P < .0005) and v_p (R² = 0.1564, P = .01; and R² = 0.2429, P = .007), but not with v_e. Multiple regression analysis showed K^trans 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.