Light distribution in intravascular low level laser therapy applying mathematical simulation: A comparative study

Intravascular low level laser therapy (ILLLT) has been applied in the treatment of many diseases for about twenty years. However, much fundamental work has not been done on its dosimetry. The study was designed to compare the difference of light distribution during ILLLT between using flat end fiber and optical fiber coupled with cylindrical light diffuser. Light distribution of He-Ne laser was processed by Monte Carlo model. The laser output was 5 mW. The diameter of both optical fibers was 400 μ. Four tissue optical parameters were chosen for simulation. The results showed that optical parameters of blood are important to determine the distribution of laser energy. The highest power density could increase to over 5000 mW/cm $^{2}$ using flat end fiber. And the laser energy was absorbed by the blood cells in very small area before the tip of flat end fiber. But when using optical fiber coupled with cylindrical light diffuser, the highest power density was about 100 mW/cm $^{2}$ . More volume of blood cells could be irradiated by laser light. In summary, optical fiber coupled with cylindrical light diffuser is superior to flat end fiber at the aspect of increasing the volume of irradiated blood and decreasing unwanted damage to blood cells during intravascular low level laser therapy.