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Figure 1 Experimental protocol. Fifteen ml of blood anticoagulated either by Argatroban or heparin containing platelets rendered fluorescent by the addition of mepacrine was perfused in a parallel-plate flow chamber composed of two glass plates, one of which was covered by immobilized type I collagen. A perfusion of an additional 15 ml of blood obtained from the same donors and treated by the same procedure, containing or not containing one of the anti-glycoprotein (GP) IIb/IIIa agents, was immediately started to perfuse on the same collagen surface for the same length of time (B). The two-dimensional and three-dimensional structures of the platelet thrombi formed on the collagen surface were continually assessed by fluorescence microscopy or by a laser confocal microscope controlled by a piezo-electric motor control system (A). In a laser confocal imaging system, the platelet thrombi were scanned from the bottom to the top (a') at a constant speed by controlling the position of objective lens (a) by piezo-motor control unit. Then, the scanning confocal images were projected from the top to the bottom at every 5° to obtain three-dimensional projection images, including projections from the top, 45° position from the horizontal axis and the side of the platelet thrombi, which are shown in Figures 3 and 4. The maximum height of the platelet thrombi (h) was calculated based on the projection image from the side of the platelet thrombi.