tip, are usually in the 20-40 MHz range, and the catheter also receives and conducts the return echo information out to the external computerized ultrasound equipment which constructs and displays a real time ultrasound image of a thin section of the blood vessel currently surrounding the catheter tip, usually displayed at 30 frames/second image. The guide wire is kept stationary and the ultrasound catheter tip is slid backwards, usually under motorized control at a pullback speed of 0.5 mm/s. (The motorized pullback tends to be smoother than hand movement by the physician.) The (a) blood vessel wall inner lining, (b) atheromatous disease within the wall and (c) connective tissues covering the outer surface of the blood vessel are echogenic, i.e. they return echoes making them visible on the ultrasound display. By contrast, the blood itself and the healthy muscular tissue portion of the blood vessel wall is relatively echolucent, just black circular spaces, in the images. Heavy calcium deposits in the blood vessel wall both heavily reflect sound, i.e. are very echogenic, but are also distinguishable by shadowing. Heavy calcification blocks sound transmission beyond and so, in the echo images, are seen as both very bright areas but with black shadows behind (from the vantage point of the catheter tip emitting the ultrasound waves). Uses IVUS, as outlined above, has been the best technology, so far, to demonstrate the anatomy of the artery wall in living animals and humans. It has led to an explosion of better understanding and research on both (a) the behavior of the atherosclerosis process and (b) the effects of different treatment strategies for changing the evolution of the atherosclerosis disease process. This has been important given that atherosclerosis is the single most frequent disease process for the greatest percentage of individuals living in first world countries. Intravascular ultrasound in the coronary anatomy While the routine use of IVUS during percutaneous coronary intervention does not improve short term outcomes, there are a number of situations in which IVUS is of particular use in the treatment of coronary artery disease of the heart. In particular in cases when the degree of stenosis of a coronary artery is unclear, IVUS can directly quantify the percentage of stenosis and give insight into the anatomy of the plaque. One particular use of IVUS in the coronary anatomy is in the quantification of left main disease in cases where routine coronary