propagation of laser light in skin by Monte Carlo- diffusion method: a fast and accurate method to simulate photon migration in biological tissues

Due to the importance of laser light penetration and propagation in biological tissues, many researchers have proposed several numerical methods such as Monte Carlo, finite element and green function methods. Among them, the Monte Carlo method is an accurate method which can be applied for different tissues. However, because of its statistical nature, Monte Carlo simulation requires a large number of photon pockets to be traced, so it is computationally expensive and time consuming. Although other numerical methods based on the diffusion method are fast, they have two important limitations: first, they are not valid near the bounder of sample and source, and second, their accuracy is less than Monte Carlo method. In this study, we combine the accuracy of Monte Carlo method and speed of the diffusion method. This hybrid method is faster than Monte Carlo Method and its accuracy is higher than the diffusion method. We first evaluate this hybrid model and the reflectance of a biological phantom is calculated by Monte Carlo method and this hybrid model. Then the propagation of laser light in the skin tissue has been studied. In this study, a combined method based on the Monte Carlo method and the diffuse equation is introduced. This hybrid method is five times faster than Monte Carlo Method, and its accuracy is higher than the diffusion method. The propagation of laser light in skin has also been studied by this hybrid method and its accuracy shows that it can be applied for laser penetration in biological tissues. It seems that this method is good for photo dynamic therapy [PDT] and optical imaging

[Determining and optimizing effective factors in laser irradiation on skin tensional strength using a hybrid DOE and DEA approach]

We investigate the characteristic of a suitable irradiation on skin's tensional strength using of experiments [DOE]. The experiments in this research are designed in two phases and data envelopment analysis [DEA] is used for performance measurement of each phase. Samples were provided from pleura as surface tissue made of collagen and elastin fibers. In each experiment, the sample was stretched before and after irradiation. Variation of the sample length was measured. Then force-length data were plotted and the slope of the fitted line was calculated. Variation in these slopes was used as a criterion to determine tissue strength variation after laser irradiation. Furthermore, the output oriented DEA model by variable return to scale was used to examine performance of the designed experiments for each phase. Results of the first phase experiments showed that the main effect of time duration was significant; but this was not the case for beam radius. Regarding polarization, only its interaction effect with time duration was significant. Results of the second phase indicated that laser effect with time duration was significant. Results of the second phase indicated that laser irradiation with parallel polarization for 10 seconds caused a greater increase in tensional strength. Resultant efficiencies of applying DEA showed that the first phase experiments were more efficient. This research has combined DEA and DOE to investigate the effects of laser on skin elasticity. Comparing the results of the two phases indicates that it is more efficient to use the experimental design of phase 1 in our experiment. So far similar future studies, we suggest using more levels for experiments of phase 1 instead of doing the experimental design in two phases