@mastersthesis{kumar96b,
  author = {K. S. Kumar},
  title = {Spectroscopy of Indocyanine Green Photodegradation},
  school = {Oregon Graduate Institute of Science and Technology},
  year = {1996},
  abstract = {In laser tissue welding, indocyanine green (ICG) is topically applied at the weld site to enhance light absorption and to minimize collateral damage. The uptake of ICG by tissues is variable, and photobleaches when exposed to high radiant exposures. To understand these processes, the intimal surface of porcine aorta stained with ICG was exposed to multiple pulses from an 804\,nm pulsed diode laser. ICG concentration was varied from 0.8--6.45\,mM. Radiant exposures between 20--70\,mJ/mm$^2$ were used with a spot size of 36\,mm$^2$ and a 5\,ms pulse duration. After each laser pulse diffusely reflected light from 450--850\,nm was obtained from the irradiated spot with an optical fiber based spectrometer. Temperatures were measured during the laser pulse. ICG penetration depth in aorta and the depth of damage were measured. Despite uniform visual appearance, ICG uptake varies by a factor of three at different spots on the same aorta. ICG bleaching is manifested by the shift in absorption peak from 530\,nm to 640\,nm. The decrease in absorption with successive pulses is an additive effect and follows a power law. The rate of decrease varies linearly with incident energy and may be independent of the concentration of ICG. Temperatures were almost constant with successive pulses. ICG is absorbed into aorta to a depth of 25\,$\mu$m but the 804\,nm light penetrates to $\sim$15\,$\mu$m. Strong fluorescence of irradiated samples suggest that some molecular reorganization of ICG occurs.},
}