Thermogram showing varicose veins in a woman's legs. Here the condition has been visualized using thermal infrared which allows us to see thermal energy or radiation more commonly referred to as heat. Thermal Infrared is found within the Infrared region on the electromagnetic spectrum. The different colors in the images represent different levels of thermal energy being emitted from the skin's surface. In this image the red and white colors show a high level of thermal energy and the blue and purple a lower level. Varicose veins occur when the valves inside the vessel which controls the direction of blood flow stop working properly and cause blood to collect in the vein pushing it out of shape. Thermography is useful in illustrating the condition as the affected veins appear 'hotter' due to thrombophlebitis (vein inflammation).