Combining laser speckle imaging and spatially modulated visible illumination to study the effect of anesthetic drugs on the optical and physiological parameters of brain

Abstract

This work employs an integrated optical imaging system to evaluate the effect of anesthetic drugs on several brain parameters including absorption, scattering, oxygen saturation, and cerebral blood flow (CBF). Two anesthetic drugs, namely ketamine-xylazine (KX) and thiopental, frequently used by researchers in mouse experiments, were investigated herein. The combined system is based on spatially modulated visible light illumination and a laser speckle based-technique. With this apparatus, a series of structured light (sinusoidal patterns) with phase shifts at each of two spatial frequencies (low and high) are projected onto the surface of a mouse brain and diffusely reflected light is acquired by a camera. A six-position filter wheel, equipped with five visible bandpass filters, is placed at the output of the projector. Then, structured illumination is blocked and a laser source illuminates the tissue while the diffusely reflected light is captured by the same camera through the remaining open hole in the wheel. In this manner, visible and laser speckle images are captured and processed off-line to reconstruct the cerebral tissue features. This work's major findings are six-fold: first, over a specific range of the spectrum a difference of more than 20% was found in the absorption coefficient presumably as a sensitivity to hemoglobin. Second, a difference of more than 20% was observed between drug types in the scattering coefficient along the entire spectral range. Third, CBF varied considerably in thiopental anesthesia throughout the experiment. Fourth, oxygen saturation level remains stable in both anesthetics. Fifth, thiopental keeps blood glucose in normal range while with KX glucose level increases. Sixth, the co-registered system is capable of revealing quantitative functional contrast and may be an attractive method in a variety of biomedical applications. Overall, these findings suggest that the choice of KX or thiopental should be carefully considered as a component of study design in research utilizing animal models.