Figure 3.

Example images of various optical imaging techniques utilized for monitoring of vascular damage during PDT. Confocal microscopy: The images show vessels before, immediately after and 1.5 hours post-PDT. The white boxes in the pre-PDT image indicate the two regions receiving light irradiation 15 minutes post intravenous PS (verteporfin, or Visudyne 16 mg/kg dose) injection. The center image clearly shows vessel damage near the light irradiation spot. The third image showcases platelet (anti-CD41 antibody red fluorescence) formation in the vessels as a response to PDT. Scale bars are 200 μm in length.²³ Photoacoustic imaging: Vascular structures in a chicken chorioallantoic membrane (CAM) tumor model are obtained using photoacoustic imaging (also known as optoacoustic imaging). PDT was performed with the PS photoporphyrin IX disodium salt that was topically applied to the model. Post-PDT, vascular damage is seen in the vessels in the area of irradiation (white arrows). The study also showed no vessel damage during light-only treatment (images not shown).²⁵ Optical frequency domain imaging: OFDI is a second generation label free OCT based angiography technique, where the modulated optical scattering due to flowing blood can be detected and differentiated from static extra-vascular tissue. Here we show OFDI images from two tumors before and 4 days after PDT. Clearly in the tumor responding to the treatment, we observe complete damage of the vascular structure. There is not significant vessel damage in the non-responding tumor. This data suggests that monitoring of vasculature can serve as another biomarker to predict the treatment outcome early in the course of treatment. Laser speckle imaging: Representative laser speckle flow index images (5mm × 4 mm) of a rodent dorsal skin fold model are shown here. Images before intervention, immediately after and 18 hours after PDT are shown. PDT caused reduction in the speckle flow index due to vascular damage in the region.²⁶ The confocal microscopy, photoacoustic images and laser speckle images are obtained from Khurana et al (2008)²³, Xiang et al (2007)²⁵ and Smith et al (2006)²⁶ respectively. The OFDI images are unpublished data from our group.