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 specific 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-specific thermal therapy in clinics.