Optogenetics provides a tool for modulating activity of specific cell types by light pulses. Different light delivery mechanisms such as single optical fiber implanted on a skull or patterned illumination can be employed to direct light to a target area. For a highly scattering medium such as brain tissue, light distribution significantly depends on the scattering parameters of the tissue as well as the inherent inhomogeneity of the specimen. For in vivo studies, blood vessels which have considerable absorption coefficient in the visible spectrum play a major role in producing such inhomogeneity. Therefore, detailed information about brain optical properties and network of blood vessels which was ignored in previous studies is necessary to accurately predict light distribution and designing light delivery mechanism during optogenetic experiments to achieve the desired optical stimulation. In this paper, light pattern preservation while considering the impact of blood vessels is investigated in a rat cortex. First, the typical optical properties of rat cortical tissue were extracted by employing double integrated sphere technique, and then, optical coherence tomography was employed to obtain structure of blood vessels on the cortex. By combining the extracted optical properties and the network of blood vessels, a three-dimensional model of a rat cortical tissue was developed. Then, a Monte Carlo simulation code was used to predict light distribution in this model for different light source configurations and wavelengths. The results confirm that presence of vessels can significantly impact the light pattern in the tissue and affect the practical depth of penetration.
Mehdi Azimipour, Farid Atry, and Ramin Pashaie, "Light pattern preservation in rodent's cortical tissue during optogenetic neuro-stimulation
(Conference Presentation)," Proc. SPIE 9706, Optical Interactions with Tissue and Cells XXVII, 970610 (Presented at SPIE BiOS: February 16, 2016; Published: 26 April 2016); https://doi.org/10.1117/12.2213201.4848609628001.
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