ABSTRACT NUMBER: ESOC2026A1973 QUANTIFYING POST-STROKE BRAIN TISSUE DEFORMATION USING TWO-PHOTON MICROSCOPY AND DEFORMABLE IMAGE REGISTRATION IN A MOUSE MCAO MODEL

Abstract Background and aims Cerebral oedema following AIS exerts mechanical forces on surrounding tissue, potentially compromising microvascular perfusion and exacerbating injury. However, the micro-scale biomechanical dynamics during early oedema formation remain poorly characterised. We quantified brain tissue deformation at micrometre resolution during AIS using two-photon microscopy (TPM) combined with deformable image registration (DIR). Methods Adult mice (n=6, both sexes, 20-30 weeks) underwent 30 minutes transient middle cerebral artery occlusion (MCAO) followed by reperfusion. TPM image stacks were acquired through a chronic cranial window at baseline, during occlusion and immediately after recanalization. Three-dimensional DIR were made using Advanced Normalisation Tools (ANTs) generated displacement vector fields. Local displacement magnitudes and directions were used to calculate volumetric changes and shear deformations. Results Local tissue deformation emerged immediately upon occlusion, notably around the pial vessels. Deformation was associated with heterogeneous local displacement up to 16 μm. Reperfusion did not restore such deformation. Rather, up to 18 μm displacement was observed upon reperfusion, as compared to baseline. These deformations resulted in local volume changes up to around 10% as well as shear deformations. These changes occurred at the micrometer scale but not at lengths scales relevant for clinical imaging. Conclusions We found substantial, very early-onset brain tissue deformation at micrometre resolution during AIS. The persistence and progression of deformation following reperfusion may reflect ongoing cytotoxic oedema and may influence reperfusion and stroke outcome. Conflict of interest All authors: Nothing to disclose.