We thank Heiland et al for their interest in our study. We would like to begin by stating that nowhere in our article does it say that the analysis of magnetic resonance (MR) perfusion imaging is “easy!” Notwithstanding, Heiland et al have raised two important issues regarding our statistics and methods that warrant clarification. Heiland et al discuss the possibility for underestimation of relative cerebral blood volume (rCBV) using dynamic susceptibility contrast MR imaging methods because of contrast agent leakage. Indeed, we thank Heiland et al for the opportunity to clarify that our methods as employed in the study did include the use of the “rather simple technique” that Heiland et al suggest of “employing a preinjection of contrast agent before a second bolus given during dynamic T2 imaging to mitigate this leakage bias.” In fact, we also employed a relatively long TR of 1.5 to 2 seconds to further reduce T1-weighting. Our methods thus include some of the very “correction techniques” that the authors address. We thus believe that we carefully mitigated the effects of underestimated rCBV values, and we do not believe this affected our study conclusions. More troubling is Heiland’s misstatement of our study conclusions. We did not state that “a reduction in CBV at 3 weeks after therapy was found to be an early predictor for true tumor progression.” In fact, we found that traditional methods (ie, mean or percentage changes of whole tumor CBV statistics) were not predictive for discriminating pseudoprogression from true progression. What we did conclude was that the application of a voxel-based difference method, referred to as parametric response map analysis, revealed the only predictive metric of early tumor progression: the fractional tumor volume that exhibited a significant decrease in rCBV at week 3 compared with baseline. These intriguing results were obtained in a small, single-institution study and require validation in a larger prospective multi-institutional study. In summary, we believe that our work continues to support the original conclusion that parametric response map analysis of perfusion MR images may provide important information regarding the assessment of response and discrimination between true progression and pseudoprogression in high-grade glioma patients receiving concurrent chemoradiation.