A novel strategy for monitoring laser thermal therapy based on changes in optothermal properties of heated tissues

Whelan, William M.
Davidson, S. R. H.
Chin, L. C. L.
Vitkin, I. A.

International Journal of Thermophysics

Journal Article

2005

26

1

233

241

Physics

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 intensity measurements are indicative of a larger 'sampling volume' of optothernial events. In porcine kidney Show moreLaser 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 intensity measurements are indicative of a larger 'sampling volume' of optothernial events. In porcine kidney ill vivo, the optical intensity at 5 mm from a laser-coupled heating fiber decreased by 49% after 2.5 min of heating at 3 W In bovine tissue ex vivo, the optical intensity at 8 mm from the heating fiber decreased by 62-83% during laser irradiation at 5 W. 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 fiber in kidney or liver. Furthermore, in the porcine kidney experiment, smoke production occurred, which is normally concomitant with high-temperature tissue charring around the heating fiber. This was observed as a complete loss in optical intensity but was not detectable in the temperature data. The measurements in this work indicate that point optical intensity may have a greater sensitivity to important optothermal events than do point temperature measurements for monitoring laser heating in tissues. Show less

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