Photo-thermal Interactions Of Laser Ablation And Selective Photothermolysis During Laser Treatments Of Skin Diseases

Researches on the photo-thermal interactions of laser ablation and selective photothermolysis(SP),which are the bases of ablative and non-ablative laser treatments of skin diseases, are the focal topics in the field of laser surgery and medicine.The photo-thermal interactions of CO2 laser skin ablation and SP were comprehensively studied here using theoretical analysis method, numerical simulation method and experimental method.A multi-zone, dynamic photo-thermal model of CO2 laser skin ablation was developed to simulate the temporal evolutions of the boundary positions of the zones, the deposited laser energy distribution, the temperature distribution and the thermal damage extent. The effects of laser power and environmental parameters, the interactions of the temperature field, the energy field and the dynamic changes in the optical and thermal properties as well as the blood perfusion rate during laser irradiation, and the effects of residual heat after laser irradiation were numerically analyzed based on the model.A 3D photo-thermal model for SP was developed using a modified 3D Monte Carlo method to simulate the laser transport in the tissue, the 3D Pennes bioheat transfer equation with variable thermal properties and latent heat effects at the vaporization temperature to calculate the temperature distribution, and the Arrhenius equation to predict the thermal damage.Numerical simulations for the temporal evolutions of the temperature distribution and the thermal damage extent were performed. The effects of blood vessel parameters within the yellow-race patients and epidermal cooling methods on the clinical outcomes of SP were analyzed.It was concluded that the term of "selective temperature distribution" provides a more comprehensive description of the mechanisms of SP than the term of "selective light distribution".According to this opinion, the feasibility and methods of improving the therapeutic outcomes of SP by increasing the selectivity of the temperature distribution were researched. Furthermore, a novel photo-thermal model of SP with dynamic changing vaporization temperature was proposed and discussed preliminarily.Experimental measurements for the dose-effect relationship of laser power and the diameter/depth of the ablation crater of ex vivo pigskin irradiated with CO2 laser, for the dose-effect relationship of laser energy and the thermal damage width of in vivo skin of white mice irradiated with 532 nm and 1064 nm laser, and for the threshold energy density of thermal damage of in vivo rabbits retina with 578 nm laser were performed. The experimental results were in agreement with the results obtained with the models proposed in chapters 2 and 3.The achievements of this project supplied scientific basis for therapy parameters selection, accurate control and effects improvement of laser treatments of skin diseases in clinical practice.