Imaging of thrombus formation in control and PECAM-1–deficient platelets. (A) Control and (B) PECAM-1–deficient mice were infused with Alexa-660–labeled anti-CD41 antibody Fab fragments before thrombus induction in cremaster muscle arterioles using a nitrogen dye laser. Thrombus formation was studied over a period of 3 minutes using a combination of widefield fluorescence and brightfield microscopy. Arrows indicate the direction of blood flow and blue arrowheads indicate the position of laser-induced endothelial damage. Videos representing the formation of thrombi shown in this figure are available as supplemental Videos S1 and S2.