Tomonori Yuasa

Noninvasive imaging of human skin hemodynamics using a digital red-green-blue camera

In order to visualize human skin hemodynamics, we investigated a method that is specifically developed for the visualization of concentrations of oxygenated blood, deoxygenated blood, and melanin in skin tissue from digital RGB color images. Images of total blood concentration and oxygen saturation can also be reconstructed from the results of oxygenated and deoxygenated blood. Experiments using tissue-like agar gel phantoms demonstrated the ability of the developed method to quantitatively visualize the transition from an oxygenated blood to a deoxygenated blood in dermis. In vivo imaging of the chromophore concentrations and tissue oxygen saturation in the skin of the human hand are performed for 14 subjects during upper limb occlusion at 50 and 250 mm Hg. The response of the total blood concentration in the skin acquired by this method and forearm volume changes obtained from the conventional strain-gauge plethysmograph were comparable during the upper arm occlusion at pressures of both 50 and 250 mm Hg. The results presented in the present paper indicate the possibility of visualizing the hemodynamics of subsurface skin tissue.

Visualization of peripheral vasodilative indices in human skin by use of red, green, blue images

Abstract. We propose a method to visualize the arterial inflow, the vascular resistance, and the venous capacitance in the skin tissue from red, green, blue (RGB) digital color images. The arterial inflow and the venous capacitance in the skin tissue are visualized based on an increase in the rate of change in the total blood concentration and the change of the total blood concentration during upper limb occlusion at a pressure of 50 mmHg. The resultant arterial inflow with the measured mean arterial pressure also provides an image of the vascular resistance in human skin. The arterial inflow, the vascular resistance, and the venous capacitance acquired by the method are well correlated with those obtained from the conventional strain-gauge plethysmograph. The correlation coefficients R between the estimated values by the method and the measurements by the SPG are calculated to be 0.83 (P<0.001) for the arterial inflow, 0.77 (P<0.01) for the vascular resistance, and 0.77 (P<0.01) for the venous capacitance. The arterial inflow and the venous capacitance in the skin tissue are significantly higher in active subjects compared with the sedentary subjects, whereas the vascular resistance was significantly lower in the active subjects compared with the sedentary subjects. The results of the present study indicate the possibility of using the proposed method for evaluating the peripheral vascular functions in human skin.

Effects of spatiotemporal averaging processes on the estimation of spectral reflectance in color digital holography using speckle illuminations.

We present the effects of spatiotemporal averaging processes on an estimation of spectral reflectance in color digital holography using speckle illuminations. In this technique, speckle fields emitted from a multimode fiber are used as both a reference wave and a wavefront illuminating an object. The interference patterns of two coherent waves for three wavelengths are recorded as digital holograms on a CCD camera. Speckle fields are changed by vibrating the multimode fiber using a vibrator, and a number of holograms are acquired to average reconstructed images. After performing an averaging process, which we refer to as a temporal averaging process in this study, using images reconstructed from multiple holograms, a spatial averaging process is applied using a smoothing window function. For the estimation of spectral reflectance in reconstructed images, we use the Wiener estimation method. The effects of the averaging processes on color reproducibility are evaluated by a chromaticity diagram, the root-mean-square error, and color differences.

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.

Color appearance of skin tissues and blood vessels: in-vitro and in-vivo experiments

The bluish appearance of veins in the skin tissue was experimentally investigated by in vivo and in vitro measurements. The color of skin surface including veins inside was evaluated by spectrophotometry and color analysis in the CIEXYZ and CIELAB colorimetric systems. The bluish appearance was successfully interpreted by the dominant wavelength and the color difference. Results for in vitro experiments showed that the degree of bluish appearance depends on the depth and diameter of blood vessels.

Investigation of temporal response in finger blood flow and concentration change in occlusion test on human arm using bio-speckle patterns

We have developed so far the method for imaging simultaneously blood flow and blood concentration change in skin tissue by using two-wavelength near infrared laser speckle patterns. We conducted experiments for human volunteers to confirm the feasibility of the method for estimating temporal response in the blood flow and blood concentration change in a human finger to occlusion on a human arm with different pressures from 50 to 150 mmHg. The results demonstrated that the response may depend on individual minimum and maximum blood pressure values.

Effects of Bright Light with Reduced Blue Light on Sleepiness on Rising: A Small Exploratory Study

Bright light therapy is a treatment modality for seasonal affective disorder and circadian rhythm disorders in which artificial light of 2,500 lux or higher at the eye is effective. Although short-wavelength visible light is more effective than long-wavelength visible light, it may be hazardous to the retina. Recently, light-emitting diodes (LEDs) have been used as the light source in bright light therapy apparatuses. We developed goggles for bright light therapy equipped with LEDs as the light source. The aim of this study was to examine the efficacy and safety of our goggles when emitting 10,000-lux light with its short-wavelength light content reduced by 30% or 50% (denoted as 30%-cut and 50%-cut light, respectively, henceforth). Six healthy young males participated in this study. They were administered no light, 50%-cut light, and 30%-cut light for 30 min early in the morning for 4 days each. Subjective sleepiness and sleep quality were evaluated by the Stanford Sleepiness Scale (SSS) and the Oguri–Shirakawa–Azumi sleep inventory MA version (OSA-MA), respectively. Subjective sleepiness evaluated by the SSS and the subscale of the OSA-MA significantly decreased with 30%-cut light compared with no light. Psychomotor performance evaluated by a calculation task improved with the 30%-cut light, although not significant after multiple comparisons were considered. No abnormality was found by ophthalmoscopy and the vision test. In conclusion, our goggles with 30%-cut light may be safe and have an awakening effect.

Development of skin tissue phantom having a shape of sulcus cutis and crista cutis

There are sulcus cutis and crista cutis on human skin surface. It is known that these affect the light propagation in human skin. To investigate it experimentally, it is desirable to reproduce sulcus cutis and crista cutis in skin tissue phantom. In this study, we made a prototype of skin tissue phantom having a shape of sulcus cutis and crista cutis, and investigated its optical properties and problems to be solved.

Monte Carlo simulation of skin image using a skin model with surface texture

Skin surface texture has an influence on light propagation in tissue and changes the impression of the skin appearance. We use Monte Carlo simulation for estimating spectral reflectance in human skin. However, the simulation was made for parallel layered model having a flat surface. In this study, we investigated to use texture-added skin model in the simulation. We confirmed that a change of intensity distribution was found when the skin surface texture was changed.

Color reproduction of human skin by spectral reflectance using RGB images and the Wiener estimation method

Skin measurements based on spectral reflectance are widely studied in the fields of medical care and cosmetics. It has the advantage that several skin properties can be estimated in the non-invasive and non-contacting manner. In this study, we demonstrate the color reproduction of human skin by spectral reflectance using RGB images and the Wiener estimation method.