Research On Light Propagation And Photo-thermal Effect In Biological Tissue

With the development of laser technology, the application of lasertechnology in biomedicine becomes more and more abroad. It has beenused for curing many diseases, just like tumor. The study of lightabsorption and photo-thermal effect in biological tissue, not only hasgreat significances in improving treatment effects, but also is helpful tothe safe diagnoses.In this paper, light propagation and the distribution of lightabsorption in biological tissue is simulated with Monte-Carlo method.Based on the distribution of light absorption, the Finite Element methodis applied to solve pennes bio-heat equation, and then the temperaturedistribution is obtained.At first, Propagation of flat and Gaussian light beam in biologicaltissue is simulated with Monte-Carlo method. Through comparing thedistribution of energy in biological tissue generated by single andmulti-beam as well as flat and Gaussian light, influence of various lightsources and the light spot size on the distribution of light absorption isanalyzed. Then the multi-beam combined sources are used to radiate thebiological tissue, and the distribution of light absorption that radiated byvarious multi-beam combined sources is obtained. The distribution oflight absorption is influenced by the distance between beams is analyzed.The results show that the laser energy is relatively concentrated while using Gaussian beam, but the lateral transport area is limited. Under thecondition of the same total power, both large single beam and smallmulti-beam can enlarge the lateral area of the light propagation effectively,but the maximal light absorption rate increases for latter approach; thedistribution of light absorption in biological tissue is influenced by thedistance between beams obviously. Then the bio-heat transfer equation issolved numerically with Finite Element Method(FEM) through Matlabprogramming. The tissue temperature distribution is calculated. Thetypical scatter dominating Nd:YAG laser coagulating the liver in theLaser Interstitial Thermotherapy (LITT) is simulated. The influence oflight source and tissue parameters to the calculation results is analyzed.The temperature of dynamical balance phenomena in vivo tissue underlow power and long time laser irradiation is discussed as well. Thesimulation results are valuable to the laser source choice and the therapyplan confirming.