This article discusses a non-invasive method for real-time measurement of cerebral blood flow using diffusion correlation spectroscopy (DCS). The technique involves the use of near-infrared light to analyze blood flow dynamics in the brain.
For non-invasive real-time cerebral blood flow measurement by diffusion correlation spectroscopy, DCS, begin with an anesthetized mouse on a platform. Shave the fur from the head to prevent interference with the DCS measurements.
Assemble a DCS probe comprising source and detector fibers. Gently place it over one of the cerebral hemispheres, with the fibers appropriately spaced for light delivery and collection.
In DCS, long-coherent, near-infrared light from a laser penetrates deep into the brain, illuminating the cerebral tissue via the source fiber.
The scattered light from the tissue along with the light scattered by the moving blood cells in the microvasculature, which act as scatterers, interfere constructively and destructively, forming an interference pattern that is recorded at the detector fiber on the tissue surface.
The moving red blood cells cause the interference pattern at the detector to change with fluctuations in the pattern's temporal intensity. The detector relays the collected signals to an avalanche photodiode. The light intensity fluctuations detected by the photodiode are transmitted to an autocorrelator.
The autocorrelator generates the normalized intensity autocorrelation function, which is fit to a simple analytical model to extract the cerebral blood flow index. This index is proportional to the blood flow within the probed cerebral tissue volume.
Estimate the average cerebral blood flow index for the brain hemisphere.
Allow the mouse to recover in the supine position on a 37-degree Celsius warming pad. After a two-minute period of stabilization, gently rest the DCS sensor over the right hemisphere of the mouse's skull, such that the top edge of the optical sensor, lines up with the back of the eye, and the side of the sensor lines up along the midline. Cup a hand over the sensor to shield it from room light, and acquire five seconds of data. Then, reposition the sensor over the left hemisphere, and acquire five seconds of left hemisphere data.
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