Short Pulse Laser Based Thermal Therapy

Abstract

Diverse precision medical applications rely on short pulse lasers, ranging from corneal sculpting and tumor ablation to diagnostic imaging and cosmetic procedures. Both laser parameters, such as laser wavelength, power, pulse width, and irradiation time, and tissue parameters, including thermophysical and optical properties and vascularization influence the temperature rises and heat affected zones achieved by any laser thermal therapy. In order to optimize the thermal dose delivered to tissues and reduce unwanted damage to surrounding healthy tissue through heat diffusion, it is critical to perform numerical modeling and analysis prior to treatment. A novel temperature controlled synthetic tissue phantom with countercurrent synthetic blood flow was designed and developed in response to the many challenges inherent to performing laboratory experiments to characterize laser-tissue interactions. A short pulse Nd:YAG laser was used to irradiate the phantoms for cases both with and without blood flow and for varying blood flow rates. A finite element model was developed to analyze the effects of blood flow on temperature rise in the tissue phantoms and was validated by the experimental measurements. Both the numerical modeling results and the experimental measurements indicated that subsurface countercurrent blood flow decreased peak surface temperature rises due to short pulse laser irradiation. Increased volumetric blood flow rates further decreased peak surface temperature rises. The novel temperature controlled vascularized synthetic tissue phantom design presents a viable alternative to live animals for use in analyzing the thermal effects of a given laser therapy and could be adapted for use in the experimental optimization of various thermal treatments.