To estimate the triplet state lifetime of Photodynamic therapy (PDT) under pulsed excitations, we measured the photosensitizer triplet state lifetimes by time resolved measurement of the singlet oxygen generated by PDT using the clinical photosensitizers, Talaporfin and Photofrin II(R). By fitting the measured curve to nonlinear least-squares statistics, the photosensitizer triplet state lifetime was obtained. For Talaporfin, the triplet state lifetime measured at a high intensity of 1.67

more »

... was 4.3 times longer than that measured at a low intensity of 0.20 MW/cm2. In the case of Photofrin II, the measured lifetime was increased to 1.1 times. These results indicated that there might be oxygen depletion at high pulsed intensities in the case of Talaporfin, which was not observed with Photofrin II.