Self temperature regulation of photothermal therapy by laser-shared photoacoustic feedback

This article describes a laser-shared photothermal system that achieves tight temperature regulation by frequency-domain photoacoustic (FD-PA) feedback. To this end, a continuous-wave laser system was designed with arbitrarily modulatable laser intensity. And, by fast alternating in the time domain between a constant laser intensity for photothermal heating and a modulated laser intensity for FD-PA temperature measurement, photothermal temperature variations are captured by FD-PA in real time. A proportional-integral-derivative (PID) controller monitors the feedback from FD-PA measurements and controls photothermal heating dose accordingly, thus stabilizing the temperature at preset values. The proposed system is demonstrated to achieve ultrafast temperature measurement at a 4 kHz rate, and with proper averaging, the measurement and regulation accuracy are 0.75 deg and 0.9 deg respectively.