IVC ligation results in IVC thrombus formation with small pulmonary embolisms, whereas intravenous thrombin injection results in large pulmonary embolisms with significantly reduced PA flow. HFUS Power-Doppler imaging (a) and pulsed-wave Doppler imaging (a) or histologic analysis (b) of the IVC revealed a thrombus formation upstream of the subtotal IVC ligation with no detectable flow (left), while no flow reduction or thrombus in the IVC was detectable after induction of experimental pulmonary embolisms after intravenous thrombin injection ((a), (b) right subpanel, (c) quantification). (d) Histologic analysis of pulmonary tissue revealed numerous large thromboemboli after thrombin injection ((d) right subpanels) which involved the large pulmonary arteries, while small thromboemboli involving the peripheral pulmonary arteries could be observed after IVC ligation ((d) left subpanels). After thrombin injection, a significant obstruction of the pulmonary arterial vascular bed ((e) right) along with a significant reduction of the PA flow ((f) right) could be observed. After IVC ligation, the degree of pulmonary arterial obstruction was significantly less ((e) middle) than in PE mice and did not result in an impaired PA flow ((f) middle). PA: pulmonary artery; 5–8 animals per group. Data are presented as mean and SEM. 1-way ANOVA with Bonferroni’s multiple comparison test.