Title: EXAMINATION OF WAVELENGTHS AND TISSUEPENETRATION OF EXCITATION LIGHT IN PDT:
Abstract: This study is concerned with the relations between the wavelengths and the penetration of the excitation light into tissue in tumor PDT. The following subjects are examined: (1) Absorption of organs; (2) relations between the energies and lifetimes of the lowest triplet states for porphyrins; and (3) possibility of two-photon excitation by Nd: YAG 1064 nm in PDT. The results obtained are summarized as follows: (1) The lengthening of the absorption wavelength of S1-S0 longer than 600nm is not necessary so; (2) the lengthening of the absorption wavelength results in the shortening of the triplet lifetime which leads to the decrease in the photochemical activities; and (3) two-photon excitation method is practically expected not to be effective in PDT.