Deformation-based morphometry: a sensitive imaging approach to detect radiation-induced brain injury?

CERVOXY ; International audience ; Background Radiotherapy is a major therapeutic approach in patients with brain tumors. However, it leads tocognitive impairments. To improve the management of radiation-induced brain sequalae, deformation-basedmorphometry (DBM) could be relevant. Here, we analyzed the significance of DBM using Jacobian determinants (JD) obtained by non-linear registration of MRI images to detect local vulnerability of healthy cerebral tissue in an animal model of brain irradiation.Methods Rats were exposed to fractionated whole-brain irradiation (WBI, 30 Gy). A multiparametric MRI (anatomical, diffusion and vascular) study was conducted longitudinally from 1 month up to 6 months after WBI. From theregistration of MRI images, macroscopic changes were analyzed by DBM and microscopic changes at the cellular and vascular levels were evaluated by quantification of cerebral blood volume (CBV) and diffusion metrics including mean diffusivity (MD). Voxel-wise comparisons were performed on the entire brain and in specific brain areas identified by DBM. Immunohistology analyses were undertaken to visualize the vessels and astrocytes.Results DBM analysis evidenced time-course of local macrostructural changes; some of which were transient andsome were long lasting after WBI. DBM revealed two vulnerable brain areas, namely the corpus callosum and thecortex. DBM changes were spatially associated to microstructural alterations as revealed by both diffusion metrics and CBV changes, and confirmed by immunohistology analyses. Finally, matrix correlations demonstrated correlations between JD/MD in the early phase after WBI and JD/CBV in the late phase both in the corpus callosum and the cortex.Conclusions Brain irradiation induces local macrostructural changes detected by DBM which could be relevant toidentify brain structures prone to radiation-induced tissue changes. The translation of these data in patients could represent an added value in imaging studies on brain radiotoxicity.