Near-infrared laser irradiation of a multilayer agar-gel tissue phantom to induce thermal effect of traditional moxibustion

Traditional moxibustion therapy can stimulate heat and blood-vessel expansion and advance blood circulation.In the present study,a novel noncontact-type thermal therapeutic system was developed using a near-infrared laser diode.The device allows direct interaction of infrared laser light with the skin,thereby facilitating a controlled temperature distribution on the skin and the deep tissues below the skin.While using a tissue-mimicking phantom as a substitute for real skin,the most important optical and thermal parameters are the absorption/attenuation coefficient,thermal conductivity,and specic heat.We found that these parameters can be manipulated by varying the agar-gel concentration.Hence,a multilayer tissue-mimicking phantom was fabricated using different agar-gel concentrations.Thermal imaging and thermocouples were used to measure the temperature distribution inside the phantom during laser irradiation.The temperature increased with the increase in the agar-gel concentration and reached a maximum value under the tissue phantom surface.To induce a similar thermal effect of moxibustion therapy,controlled laser-irradiation parameters such as output power,wavelength and pulse width were obtained from further analysis of the temperature distribution.From the known optothermal properties of the patient's skin,the temperature distribution inside the tissue was manipulated by optimizing the laser parameters.This study can contribute to patient-specic thermal therapy in clinics.

ASSESSMENT OF OPTICAL CLEARING INDUCED IMPROVEMENT OF LASER SPECKLE CONTRAST IMAGING

Laser Speckle Contrast Imaging(LSCI)plays an important role in studying blood flow,but suffers from limited penetration depth of light in turbid tissue.The strong scattering of tissue obviously reduces the image contrast which decreases the sensitivity to flow velocity.Some image processing or optical clearing methods have been proposed to lessen the deficiency,but quantitative assessment of improvement is seldom given.In this study,LSCI was applied to monitor the blood flow through a capillary embedded within various tissue phantoms at depths of 0.25,0.45,0.65,0.85 and 1.05 mm,and the flow velocity in capillary was controllable from 0 to 4mm/s.Here,glycerol,a common optical clearing agent,was mixed with Intralipid at different volume ratio to make the reduced scattering coefficient of tissue phantom decrease from 13.00 to 0.50 cm−1.The quantitative analysis demonstrates that the optical clearing method can obviously enhance the image contrast,imaging depth,and sensitivity to blood flow velocity.Comparing the Laser Speckle Contrast Analysis methods and the optical clearing method,we find that for typical turbid tissue,the sensitivity to velocity estimated by the Laser Speckle Temporal Contrast Analysis(LSTCA)is twice of that by the Laser Speckle Spatial Contrast Analysis(LSSCA);while the sensitivity to velocity estimated by using the two analysis methods has a 10-fold increase,respectively,if addition of glycerol makes the reduced scattering coefficient of tissue phantom decrease by 30%.Combining the LSTCA and the optical clearing method,the sensitivity to flow velocity will be further enhanced.