A Closed-loop Control Approach for Online Laser Power Adjustment During a Heat Therapy Process in the Presence of Nanoparticles
S.E. Razavi
In this article a closed-loop control methodology is proposed for online control of temperature rising by laser power and targeted nanoparticles during the heat therapy process; in fact, for appropriate temperature increment in a tumour mass exposed to laser radiation in the presence of nanoparticles, the radiation profile was adjusted online through a control strategy. Controlling of temperature rise due to the presence of nanoparticle in the tumour site is obligatory because it can be harmful for normal tissues. So, the tumour boundary temperature must be controlled. The designed control mechanism was based on a proportional integral derivative (PID) controller. Coefficients of the PID controller were estimated through an optimization algorithm called imperialist competitive algorithm (ICA). Difference between the desired temperature of the tumour mass and its actual temperature in each instance was the controller input; in contrast, the controller output was the laser power adjustment in each instance. The simulation studies were carried out on a physiological model of virtual tissue containing the tumour mass, healthy tissue and nanoparticles (NP). In the first step, optimal size of the used nanoparticles (GaAs/AlGaAs) was computed to guarantee radiation of wavelengths near the infrared (IR) wavelengths when being exposed to the laser radiation with wavelengths of 680 to 720 nm. The Schrödinger equations and effective mass equation were solved to obtain optimal size of the nanoparticles. In the next step, performance of the presented closed-loop controller was evaluated using simulation studies on the model of virtual tissue. The results showed desirable control of heat variations generated by quantum-dots (QD) during the heat therapy. Desirable optical-thermal responses of the laser-radiated tissue certified attractive performance of the proposed control methodology.
Keywords: Laser, nanoparticles (NP), quantum-dots (QD), power intensity, proportional integral derivative (PID) controller, imperialism competitive algorithm (ICA), finite element method (FEM)