earticle

영어

Cerebral cortex is a few mm thick and it has both layered and column structures whose size is submillimeter scale. When the neural activity in the small region of cerebral cortex is augmented, blood flow to the region increases to supply sufficient oxygen, which is called neuro-vascular coupling. To elucidate such coupling it is necessary to know microvascular structure and function 3-dimensionally with sufficient spatial resolution. However, microvessels deeper than about 100 μm such as the penetrating arterioles are difficult to observe by light microscope. Although MRI can observe living structures throughout the whole body, its spatial resolution is in the order of mm. Optical coherence tomography (OCT) has a capability of imaging living tissues up to a few mm depth with around 10 μm spatial resolution. It is still difficult to discriminate deeply embedded microvessels from the surrounding tissue by OCT structural image alone. The Doppler effects due to the blood flow can be used as a marker to find out blood vessels embedded within the tissue. In this study, the Doppler-OCT technique was applied to detect and visualize microvessels deeply embedded in the cerebral cortex of the rat. The OCT system used in our study incorporates a broad band near infrared light source with central wavelength of 1310 nm. Its axial and lateral resolutions are about 10 μm and 14 μm, respectively. The male Wistar rats of 150-200 g were used for cerebral preparation. After they were anesthetized, the cranial window about 3x5 mm2 was created in the parietal region while the dura mater was kept intact. The OCT signal obtained from within the cortical tissue was analyzed using short time Fourier transform (STFT) to get spectrogram, which displays the change in power spectrum of the signal with time. The OCT signal originating from the flowing blood suffers from the Doppler frequency shift and is clearly distinguished from the signal of surrounding tissue at rest in the spectrogram. Furthermore the blood flow velocity can be measured with a time resolution of a few msec, which is sufficient for analysis of pulsatile blood flow. As a result, microvessels penetrating into the cerebral cortex from the surface as well as microvessels running deep in the cortex were unveiled up to over 1 mm depth. The blood velocity distribution was also obtained inside the microvessel and was superimposed on the OCT structural image, where the position and passage of microvessels were visualized on the tomographic image of OCT. The information of structure and blood flow of microvessels in the direction of depth can help us to understand blood flow regulation among the layers of cerebral cortex.