Intravascular ultrasound (IVUS) is a catheter-based diagnostic tool that provides a real-time, high-resolution, tomographic view of coronary arteries. There are basically two types of commercially available IVUS imaging catheters: a single-element mechanically rotated transducer and a phased-array electronic system. Mechanical systems comprise a flexible cable with a single rotation transducer that revolves at 30 revolutions per second emitting and receiving ultrasound signals every 1º increment. Phased-array catheters contain a 64-element annular array that enables a coordinated emission of the ultrasound signal. Quantitative angiographic measurements can be misleading since this technique only allows the evaluation of the profile of the lumen. A meta-analysis of angiographic studies has concluded that the magnitude of the antiatherosclerotic effects is small compared with the effects of statins on the prevention of cardiovascular events. The relation between shear stress and plaque vulnerability is currently the subject of intensive research efforts.