Selective occlusion of a blood vessel is achieved by selectively damaging endothelial cells at a target location in the blood vessel, resulting in the formation of a fibrin clot proximate to the damaged endothelial cells. Additional fibrinogen can then be introduced into the blood vessel if occlusion is not achieved, as the fibrinogen is converted to fibrin by enzymes released by the exposed thrombogenic tissue and activated platelets. Endothelial cells are selectively damaged using thermal effects induced by ultrasound, by mechanical effects induced by ultrasound, or by mechanical effects produced by a tool introduced into the blood vessel (such as a catheter-based tool). A particularly preferred technique for selectively damaging endothelial cells involves introducing an ultrasound activatable agent into the blood vessel, and causing cavitation in that agent using pulses of high-intensity focused ultrasound having a duration insufficient to induce thermal damage in adjacent perivascular tissue.