Dynamic susceptibility contrast perfusion imaging of radiation effects in normal-appearing brain tissue: Changes in the first-pass and recirculation phases

Purpose: To identify radiation-induced changes in the cerebral vasculature of healthy tissue in the first four months following radiotherapy through the analysis of dynamic-susceptibility contrast perfusion imaging. Materials and Methods: Dynamic gradient-echo imaging was performed on 22 patients during injection of a bolus of Gd-DTPA contrast. The relative cerebral blood volume (rCBV), maximum Delta R2* of the first passage of the bolus, and a recirculation parameter were derived from gamma-variate fits of the dynamic data. The white matter (WM) rCBV and peak heights were estimated through correlation with segmented T1-weighted images. A percent recovery to baseline was also computed to further describe the recirculation phase. Results: A significant,elevation of the recirculation phase was observed at doses > 15 Gy at two months following radiotherapy. This was reflected in an increased recirculation parameter in the fitted curves in the 15-30, 30-45, and > 45 Gy dose groups to 2.8%, 3.8%, and 2.4% above the < 15 Gy voxels, as well as in a decline in percent recovery to baseline. A trend toward lower rCBV and peak heights was observed at that same time point. Conclusion: The observed results suggest a dose-dependent decline in vessel density and increase in vascular permeability and/or tortuosity in irradiated normal-appearing brain tissue at two months following radiotherapy.