Temperature distribution in deep tissue phantom during laser irradiation at 1,064 nm measured by thermocouples and thermal imaging technique

Moxibustion generates heat stimulation which expands blood vessels and promotes blood circulation. Furthermore, moxibustion provokes the release of diffuse noxious inhibitory controls (DNIC) to treat and prevent diseases. However, inherent drawbacks, such as pain, burn scars, smoke and bad smells, limit its use. A novel noncontact-type laser therapy device having effect similar to that of commercial moxibustion is being developed using a 1,064-nm infrared (IR) diode-pumped solid state (DPSS) laser. The therapy device allows direct interaction of laser light with the skin rendering temperature distribution both on the skin surface and deep under the skin. We devised a sample holder containing a tissue phantom to measure the three-dimensional temperature distribution with thermocouples inserted deep inside the phantom. Agar gel of 2.5% concentration was used as the tissue phantom in our experiments. Our results revealed that the maximum temperature occurred far below the surface of the tissue phantom, which was heated by laser irradiation at 1,064 nm. This occurrence was also confirmed by a thermal imaging method. In contrast, temperature gradually decreased through the depth of the tissue phantom heated with commercial moxibustion. Simple analytical models were constructed to explain the underlying heat-transfer mechanisms involved in moxibustion and laser irradiation.