Tumour enhancing fraction (EnF) in glioma: relationship to tumour grade

The aim of this research was to determine whether the proportion of a tumour that enhances (enhancing fraction, EnF) and changes in EnF with enhancement threshold differ between low and high grade glioma. Forty-four patients (45 gliomas comprising 16 grade II, 5 grade III and 24 grade IV) were studied. Imaging included pre- and post-contrast-enhanced T-1-weighted sequences and T-1-weighted DCE-MRI. Thresholded enhancement maps were generated for each tumour by using a range of values of the initial area under the contrast concentration curve (IAUC). A plot of EnF versus threshold value was generated. We examined the relationship between tumour grade and enhancement metrics including: EnF (threshold IAUC > 0 mMol s), EnF (threshold IAUC > 2.5 mMol s), initial slope of the EnF/threshold curve (a,EnF), IAUC, and two previously described signal-intensity-based metrics. EnF, defined as the proportion of tumour showing any enhancement (threshold IAUC > 0 mMol s), showed no difference between low and high grade glioma. All other measures demonstrated significant differences between grade II and IV, and low (grade II) and high grade (grades III/ IV) gliomas (p < 0.01). Two measures, a,EnF and Pronin's measure of enhancement, showed differences between grade III and IV (p < 0.05). No measure separated grade II from III. Metrics which describe the enhancing fraction and its variation with enhancement threshold a,EnF show considerably different behaviour in low and high grade tumours. These observations suggest that these metrics may provide important biological information concerning tumour biology and therapeutic responses and encourage further research to characterise and validate these novel biomarkers.