Microvascular photodynamic effects determined in vivo using optical Doppler tomography

Vascular responses were monitored to understand the role of the microvascul ature 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), d rug-light intervals were 20 min or 8 h, Jejunal blood vessels were exposed to 12 J/cm(2) at 690 nm (with BPD) or at 630 nm (with Photofrin), Optical D oppler tomography (ODT) was used to evaluate PDT-induced changes in vessel diameter and blood dow. 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 o r overshoot occurred. Veins became occluded with no restoration of the vess el lumen. At longer drug-light intervals, vasoconstriction diminished and v enodilation was observed. With Photofrin, vasoconstriction and venodilation increased with the drug-light interval. Application of a higher light dose (48 J/cm(2)) resulted in irreversible hemostasis. ODT can be used to study changes in lumen diameter and blood flow, which are important diagnostic p arameters of PDT.