Challenges for the functional diffusion map in pediatric brain tumors

Background. The functional diffusionmap (fDM) has been suggested as a tool for early detection of tumor treatment efficacy.We aim to study 3 factors that could act as potential confounders in the fDM: areas of necrosis, tumor grade, and change in tumor size. Methods. Thirty-four pediatric patientswith brain tumorswere enrolled in a retrospective study, approved by the local ethics committee, to examine the fDM. Tumorswere selected to encompass a range of types and grades. A qualitative analysis was carried out to compare how fDM findings may be affected by each of the 3 confounders by comparing fDM findings to clinical image reports. Results.Results show that the fDM in areas of necrosis donot discriminate between treatment responseand tumor progression. Further-more, tumorgradealters thebehaviorof the fDM: adecrease in apparentdiffusion coefficient (ADC) is a signof tumor progression inhigh-grade tumors and treatment response in low-grade tumors. Our results also suggest using only tumor area overlap between the 2 time points analyzed for the fDM in tumors of varying size. Conclusions. Interpretation of fDM results needs to take into account the underlying biology of both tumor and healthy tissue. Carefu