Intraoperative fluorescence angiography allows confirmation of the location of the coronary arteries and assessment of bypass graft function during coronary artery bypass procedures. The intraoperative fluorescence imaging system consists of a video camera and a laser diode that emits monochromatic light. The camera, guided by a range-detector diode, is positioned a safe distance above the heart. A small amount of indocyanine green (ICG) dye is then administered as a central venous injection. This dye fluoresces when illuminated using laser energy and the images are recorded digitally. Currently the technique is only semiquantitative, in that it permits assessment of graft flow as 'excellent', 'satisfactory' or 'poor' – it cannot provide an exact measure of graft flow. The penetrating depth of the laser beam is only around 1 mm, limiting the use of this technique to certain grafts. For more details, see the overview.