Izumi Nishidate

Imaging of rat brain using short graded-index multimode fiber

Clinically it is important to image structures of brain at deeper areas with low invasions, for example, the pathological information is not obtained enough from the white matter. Preliminarily we have measured transmission images of rat brain using the short graded-index multimode fiber (SMMF) with the diameter of 140μm and length of 5mm. SMMF (core diameter, 100μm) was cut using a fiber cleaver and was fixed in a jig. Fiber lengths inside and outside jig were 3mm and 2mm, respectively. The jig was attached at the 20x objective lens. The conventional optical microscope was used to measure images. In basic characteristics, it was confirmed that the imaging conditions almost corresponded to calculations with the ray-transfer matrix and the spatial resolution was evaluated at about 4.4μm by measuring the test pattern. After euthanasia the rat parietal brain was excised with thickness around 1.5mm and was set on the slide glass. The tissue was illuminated through the slide glass by the bundle fiber with Halogen lamp. The tip of SMMF was inserted into the tissue by lifting the sample stage. The transmission image at each depth from 0.1mm to 1.53mm was measured. Around the depth of 1.45mm, granular structures with sizes of 4-5μm were recognized and corresponded to images by HE stained tissue. Total measurement time was within 2 hours. The feasibilities to image the depth of 5 mm with SMMF have been shown.

In vivo imaging of cerebral hemodynamics and regional oxygen saturation in rats with a digital red-green-blue camera

The concentrations of oxygenated and deoxygenated hemoglobin and regional oxygen saturation in rat brains were visualized based on the RGB images acquired while changing fraction of inspired oxygen.

Noncontact imaging of plethysmographic pulsation and spontaneous low-frequency oscillation in skin perfusion with a digital red-green-blue camera

A non-contact imaging method with a digital RGB camera is proposed to evaluate plethysmogram and spontaneous lowfrequency oscillation. In vivo experiments with human skin during mental stress induced by the Stroop color-word test demonstrated the feasibility of the method to evaluate the activities of autonomic nervous systems.

Multispectral imaging of hemodynamics in exposed brain of rat during cortical spreading depression using Wiener estimation method

To visualize hemodynamics in cerebral cortex of in vivo rat brain during cortical spreading depression, we investigate a spectral reflectance imaging technique based on the Wiener estimation for a digital RGB camera.

Noncontact plethysmographic imaging based on diffuse reflectance spectroscopy using a digital RGB camera

To perform a contactless plethysmographic imaging, we investigated a method to estimate the concentrations of oxygenated and deoxygenated blood in human skin tissue from RGB images, based on the Monte Carlo simulation.

In vivo imaging of tissue scattering parameter and cerebral hemodynamics in rat brain with a digital red-green-blue camera

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.

Rat brain imaging using full field optical coherence microscopy with short multimode fiber probe

We demonstrated FF OCM(full field optical coherence microscopy) using an ultrathin forward-imaging SMMF (short multimode fiber) probe of 50 μm core diameter, 125 μm diameter, and 7.4 mm length, which is a typical graded-index multimode fiber for optical communications. The axial resolution was measured to be 2.20 μm, which is close to the calculated axial resolution of 2.06 μm. The lateral resolution was evaluated to be 4.38 μm using a test pattern. Assuming that the FWHM of the contrast is the DOF (depth of focus), the DOF of the signal is obtained at 36 μm and that of the OCM is 66 μm. The contrast of the OCT images was 6.1 times higher than that of the signal images due to the coherence gate. After an euthanasia the rat brain was resected and cut at 2.6mm tail from Bregma. Contacting SMMF to the primary somatosensory cortex and the agranular insular cortex of ex vivo brain, OCM images of the brain were measured 100 times with 2μm step. 3D OCM images of the brain were measured, and internal structure information was obtained. The feasibility of an SMMF as an ultrathin forward-imaging probe in full-field OCM has been demonstrated.

Evaluation of spontaneous low-frequency oscillations in cerebral hemodynamics with time-series red-green-blue images

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.

Non-contact measurement of pulse wave velocity using RGB cameras

Non-contact measurement of pulse wave velocity (PWV) using red, green, and blue (RGB) digital color images is proposed. Generally, PWV is used as the index of arteriosclerosis. In our method, changes in blood volume are calculated based on changes in the color information, and is estimated by combining multiple regression analysis (MRA) with a Monte Carlo simulation (MCS) model of the transit of light in human skin. After two pulse waves of human skins were measured using RGB cameras, and the PWV was calculated from the difference of the pulse transit time and the distance between two measurement points. The measured forehead-finger PWV (ffPWV) was on the order of m/s and became faster as the values of vital signs raised. These results demonstrated the feasibility of this method.

In vivo estimation of light scattering and absorption properties of rat brain using single reflectance fiber probe during anoxic depolarization

Diffuse reflectance spectroscopy using fiber optic probe is one of most promising technique for evaluating optical properties of biological tissue. We present a method determining the reduced scattering coefficients μs’, the absorption coefficients μ a, and tissue oxygen saturation StO2 of in vivo brain tissue using single reflectance fiber probe with two source-collector geometries. In the present study, we performed in vivo recordings of diffuse reflectance spectra and the electrophysiological signals for exposed brain of rats during normoxia, hyperoxia, hypoxia, and anoxia. The time courses of μa in the range from 500 to 584 nm and StO2 indicated the hemodynamic change in cerebral cortex. Time courses of μs’ are well correlated with those of μa in the range from 530 to 570 nm, which also reflect the scattering by red blood cells. On the other hand, a fast decrease in μs’ at 800 nm were observed after the respiratory arrest and it synchronized with the negative deflection of the extracellular DC potential. 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 μs’ at 800 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 and loss of tissue viability in brain tissue.