Evaluation of changes in gliomas structural features after chemotherapy using DTI-based Functional Diffusion Maps (fDMs): a preliminary study with intraoperative correlation.

The characterization of tumoral tissue obtained by splitting the diffusion tensor into its isotropic (p) and anisotropic (q) components allows to reveal tumoral and peritumoral abnormalities in gliomas that are not apparent on conventional MR imaging and to detect the presence of microscopic tumor cells infiltration in white matter around the edge of the gross tumor, as confirmed by image guided biopsies [1]. The evaluation of this microscopic infiltration could also give better insights into the assessment of response to chemotherapy, as changes in pattern of water diffusion after successful or failed treatment could occur prior to alteration in size, thus reflecting a dynamic reorganization of the heterogeneous tumor structure during chemotherapy. Recently, changes in diffusion and perfusion metrics during treatment have been evaluated by parametric response maps, that allow a voxel-by-voxel comparison of measures over time with respect to a baseline map. This voxel-wise approach, when referred to the evaluation of ADC changes, is termed the functional diffusion maps (fDMs) [2,3]. In this study, we aim to evaluate diffusion tensor decomposition-derived metrics in a functional manner, by applying fDMs analysis to isotropic (p) and anisotropic (q) maps during neuroradiological follow-up of patients undergoing to dose-dense temozolomide chemotherapy before second-look surgery; changes in diffusion parameters within tumor tissue are correlated both with neurophysiological data from intraoperative subcortical mapping and histopathological findings from specimens obtained from image-guided tumor biopsies.