Multiscale x-ray phase-contrast tomography in a mouse model of transient focal cerebral ischemia

Cerebral ischemia as a consequence of blood vessel occlusion is associated with a lack of both oxygen and high-energy phosphates within the brain tissue, all of which leading to irreversible cell injury. The latter affects neurons and glia alike, albeit to a different extent. Visualizing these cellular injuries has long been a focus of experimental stroke research with application of immunohistochemistry and others as standard techniques. Immunohistochemistry, however, is a destructive imaging technique with non-isotropic resolution. In its conventional form, histological techniques only visualize the two-dimensional (2d) tissue structure of a thin brain section using optical microscopy and specific stainings. Herein, we extend the structural analysis of mouse brain tissue after focal cerebral ischemia to the third dimension. Without the need of tissue slicing or staining, we demonstrate a reconstruction of the three-dimensional (3d) tissue structure via microfocus computed tomography (µ-CT). In this innovative approach for the display of post-stroke brain injury, contrast of the weakly absorbing and unstained tissue is generated by free-space propagation of the x-ray wavefront between the object and the detector. The spatial coherence required for this form of x-ray phase-contrast CT is achieved by an advanced liquid jet x-ray anode. Choosing suitable geometry and detection parameters, our data shows that recordings at two different magnifications and fields of view can be combined as a single elegant approach for visualization of the ischemic area. This technique allows for detection of the stroke area as in conventional imaging techniques of whole brains, followed by imaging on the level of single cells, which can be subsequently segmented based on their intrinsic density contrast. In conclusion, the demonstrated multi-scale approach of µ-CT enables the observation of structural alterations caused by an ischemic stroke in a mouse model from the level of the whole organ down to single cells, at isotropic resolution without slicing and staining.