We investigated a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation (StO2), and the scattering power b in the expression of musp=a(lambda)^-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, Monte Carlo simulation (MCS) for light transport in brain tissue is used to specify a relation among the RGB-values and the concentration of oxygenated hemoglobin (CHbO), that of deoxygenated hemoglobin (CHbR), and the scattering power b. In the present study, we performed sequential recordings of RGB images of in vivo exposed brain of rats while changing the fraction of inspired oxygen (FiO2), using a surgical microscope camera system. The time courses of CHbO, CHbR, CHbT, and StO2 indicated the well-known physiological responses in cerebral cortex. On the other hand, a fast decrease in the scattering power b was observed immediately after the respiratory arrest, which is similar to the negative deflection of the extracellular DC potential so-called anoxic depolarization. It is said that the DC shift coincident with a rise in extracellular potassium and can evoke cell deformation generated by water movement between intracellular and extracellular compartments, and hence the light scattering by tissue. Therefore, the decrease in the scattering power b after the respiratory arrest is indicative of changes in light scattering by tissue. The results in this study indicate potential of the method to evaluate the pathophysiological conditions and loss of tissue viability in brain tissue.
KEYWORDS: Brain, Tissues, Cerebral cortex, Mode conditioning cables, Hemodynamics, Cameras, In vivo imaging, Digital cameras, RGB color model, Monte Carlo methods, Diffuse reflectance spectroscopy
Nervous system relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the waste products of metabolism. Failure of these mechanisms is found in a number of devastating cerebral diseases, including stroke, vascular dementia, brain injury and trauma. Vasomotion which is the spontaneous low-frequency oscillation derived by the contraction and relaxation of arterioles and appears to be an intrinsic property of the cerebral vasculature, is important for monitoring the cerebral flow, tissue metabolism and health status of brain tissue. In the present study, we investigated a method to visualize the spontaneous low-frequency oscillation of cerebral blood volume based on the sequential RGB images of exposed brain.
The brain relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the
waste products of metabolism. It is thus one of the most tightly regulated systems in the body, whereby a whole range of
mechanisms act to maintain this supply, despite changes in blood pressure etc. Failure of these mechanisms is found in a
number of devastating cerebral diseases, including stroke, vascular dementia and brain injury and trauma. Spontaneous
contraction and relaxation of arterioles (and in some instances venules) termed vasomotion has been observed in an
extensive variety of tissues and species. Vasomotion has a beneficial effect on tissue oxygenation and enhance blood
flow. Although vasomotion is strictly a local phenomenon, the regulation of contractile activity of vascular smooth
muscle cells is dependent on the complex interplay between vasodilator and vasoconstrictor stimuli from circulating
hormones, neurotransmitters, endothelial derived factors, and blood pressure. Therefore, evaluation of the spontaneous
oscillations in cerebral vasculatures might be a useful tool for assessing risk and investigating different treatment
strategies in neurological disorders, such as traumatic brain injury, seizure, ischemia, and stroke. In the present study, we
newly propose a method to visualize the spontaneous low-frequency oscillation of cerebral blood volume based on the
sequential RGB images of exposed brain.
KEYWORDS: Scattering, Brain, Cameras, Tissues, Digital cameras, RGB color model, Oxygen, In vivo imaging, Neuroimaging, Monte Carlo methods, Light scattering, Hemodynamics
We propose a rapid imaging method to monitor the spatial distribution of total hemoglobin concentration (CHbT), the tissue oxygen saturation, and the scattering power b in the expression of μs’=aλ-b as the scattering parameters in cerebral cortex using a digital red-green-blue camera. In the method, the RGB-values are converted into the tristimulus values in CIEXYZ color space which is compatible with the common RGB working spaces. Monte Carlo simulation (MCS) for light transport in tissue is used to specify a relation among the tristimulus XYZ-values and the concentration of oxygenated hemoglobin, that of deoxygenated hemoglobin, and the scattering power b. In the present study, we performed sequential recordings of RGB images of in vivo exposed rat brain during the cortical spreading depolarization evoked by the topical application of KCl. Changes in the total hemoglobin concentration and the tissue oxygen saturation imply the temporary change in cerebral blood flow during CSD. Decrease in the scattering power b was observed before the profound increase in the total hemoglobin concentration, which is indicative of the reversible morphological changes in brain tissue during CSD. The results in this study indicate potential of the method to evaluate the pathophysiological conditions in brain tissue with a digital red-green-blue camera.
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