Vascular responses were monitored to understand the role of the microvasculature in tumor destruction as a result of photodynamic therapy (PDT). Rats received an intravenous dose of 2 mg/kg Benzoporphyrin Derivative (BPD), at 20 min, 4 h, or 7 h before laser irradiation. With Photofrin (10 mg/kg), drug-light intervals were 20 min or 8 h. Jejunal blood vessels were exposed to 12 J/cm2 at 690 nm (with BPD) or at 630 nm (with Photofrin). Optical Doppler tomography (ODT) was used to evaluate PDT-induced changes in vessel diameter and blood flow. At the shortest drug-light time interval (20 min), BPD-mediated PDT caused transient constriction of arteries, accompanied by decreased blood flow, followed by vasodilation until baseline was reached or overshoot occurred. Veins became occluded with no restoration of the vessel lumen. At longer drug-light intervals, vasoconstriction diminished and venodilation was observed. With Photofrin, vasoconstriction and venodilation increased with the drug-light interval. Application of a higher light dose (48 J/cm2) resulted in irreversible hemostasis. ODT can be used to study changes in lumen diameter and blood flow, which are important diagnostic parameters of PDT.

Optical Doppler tomography (ODT) is an imaging modality that takes advantage of the short coherence length of a broad-band light sources to perform micrometer-scale, cross-sectional imaging of tissue structure and blood flow dynamics simultaneously. We review in this paper the principal of ODT and its applications. Results from in vitro and in vivo model studies demonstrated that ODT can map the blood flow velocity profile with high spatial resolution in scattering medium. ODT detection mechanisms are illustrated using Monte Carlo simulations. The application of ODT to image brain hemodynamics is demonstrated. Finally, we discuss the limitations of the current technology and application of a phase resolved technique to improve image speed and quality.