In vivo imaging of the rat cerebral microvessels with optical coherence tomography

A technique called optical coherence tomography (OCT) was applied to in vivo observation of microcirculation in the rat cerebral cortex. The OCT system used in this study provided cross-sectional images of the cerebral cortical tissue up to about 1 mm depth with longitudinal resolution up to 8 microm. It could visualize cross-sectional structure of the dura, arachnoid membrane, cortical tissue, and pial microvessels through the cranial window. Pial microvessels with diameter larger than several 10 microm could be detected to observe their cross-sectional shape, while the microvessels within the cortical tissue with smaller diameter were not discernible. The OCT observation revealed that the pial microvessels showed different spatial configurations depending on the cerebral preparations with intact dura and without dura. Stimulus responses of the somatosensory cortices were also different among the preparation methods; Delayed swelling of the cortical surface appeared in the somatosensory cortex following the electrical stimulation of the hind paw in the case of dura removal, which was restricted to a thin surface layer with less than several 10 microm. It is considered to reflect the reactive hyperemia accompanying the neuronal activation. Doppler frequency shift due to the blood flow was detected in pial arterioles. This phenomenon is promising to provide the velocity profile within microvessels and may be applicable to the functional imaging of the brain.