Thrombosis. False-colour scanning electron micrograph (SEM) of a thrombus (clot) of red blood cells inside a blood vessel. Blood clotting may occur after an injury in order to seal the damaged tissues but may also develop inside major blood vessels. In this case they are known as thrombi and obstruct the normal flow of blood leading to dangerous conditions such as heart attacks and strokes. The formation of thrombi is encouraged by the deposition of atheroma (fatty deposits), a condition known as atherosclerosis, along the walls of blood vessels. Magnification: x110 at 6x7cm size. x150 at 4x5"~LANDSCAPE"