MRI-based vessel function maps for high-resolution differentiation between tumor and nontumoral tissues in brain tumor patients.

Abstract

2078 Background: Changes in enhancement seen in post treatment brain MRIs in primary and secondary brain malignancies often mimic tumor progression (pseudoprogression, radiation necrosis). Conventional MRI cannot differentiate tumor progression from treatment related effects resulting in suboptimal patient management. Methods: The application of delayed contrast extravasation MRI for depicting unique vessels characteristics with high resolution and high sensitivity to subtle BBB disruption is demonstrated in 17 GBM and 15 brain metastases patients undergoing standard chemoradiation and radiosurgery respectively. Results: 2 primary vessel function populations were defined: a slow population where contrast clearance from the tissue was slower than accumulation, and a fast population where clearance was faster than accumulation. Ten stereotactic biopsies acquired from GBM patients showed complete correlation with the maps, confirming the discrimination between fast population regions, reflecting morphological active tumor and slow regions reflecting necrosis/treatment-induced changes. Typical fast population vessel morphology consisted of proliferating endothelial cells, dilated lumen, peri vascular fibrosis and glumeroloid vessels, while slow regions consisted of necrotic vessels, in agreement with the observed MRI vessel function. The fast component volume 3 weeks post treatment was significantly correlated with the fast volume 4 (r2=0.84, p<0.0005) and 6 months (r2=0.84, p<0.01) later, suggesting early prediction of response. Brain metastases histology showed similar results: 5 brain metastases with a fast population component were confirmed histologically to contain morphologically active tumor. One metastasis consisting of the slow population only significantly decreased in volume in the following MRIs. Conclusions: These results demonstrate the feasibility of applying our delayed contrast extravasation high resolution function vessel maps for improving patient management by clearly depicting tumor and non-tumoral tissues in patients with primary and secondary brain malignancies undergoing standard chemoradiation or radiosurgery.