A Novel Strategy For Monitoring Laser Thermal Therapy Based on Changes in Optothermal Properties of Heated Tissues

Laser thermal therapy uses near-infrared optical energy to heat and thereby treat diseased tissues such as solid tumors. A method to monitor the progress of laser thermal therapy by detecting temperature-induced changes in optical propagation has been developed. The advantage of a point optical monitoring strategy over a conventional point temperature monitoring approach is that optical iIntensity measurements are indicative of a larger ‘sampling volume’ of optothermal events. In porcine kidney in vivo, the optical iIntensity at 5mm from a laser-coupled heating fiber decreased by 49% after 2.5 min of heating at 3W. In bovine tissue ex vivo, the optical iIntensity at 8mm from the heating fiber decreased by 62–83% during laser irradiation at 5W. This substantial decrease in optical penetration is consistent with increased optical scattering by thermally damaged tissue (i.e., kidney and liver) around the heating fiber. This damage was not detected by a temperature sensor placed at the same distance from the heating