Intravascular ultrasound (IVUS), a relatively new imaging modality, has become part of the expanding armamentarium of imaging devices used during both coronary and peripheral interventions.72, 73 In the past 5 years IVUS has made large strides in improvement of resolution, gray scale, and overall image quality. This, in combination with the development of more user friendly and reliable IVUS units, has allowed for significant expansion of the potential roles for IVUS during catheter directed interventions.72 As percutaneous interventions become more complex, imaging with various modalities other than angiography becomes more important. Endovascular graft placement and aortic fenestration for dissections are two examples of newer imaging guided procedures that rely on specific information obtained either prior to or during the intervention that cannot be obtained with angiography alone.65, 68 Results, outcomes, and patency projections of more conventional interventions such as percutaneous transluminal angioplasty (PTA), atherectomy, and stent placement may be betterpredicted with the additional information provided by IVUS. Angiography has been and will most probably remain the indispensable reference standard for vascular evaluation, especially during interventional procedures. Advances in catheter technology, digital imaging systems, and contrast technology have allowed angiography to evolve into a relatively safe, time efficient, and reproducible diagnostic tool that is universally accepted by physicians of all specialties who interrogate vascular anatomy. Nonetheless, significant limitations exist with angiography and discrepancies between pathologically proven specimens and angiography have long been recognized.14, 16, 22, 30, 53, 59, 64, 68, 75 Angiography provides two-dimensional (2-D) longitudinal images of patent vessel lumens. It provides no information regarding the vessel wall, morphology of plaque, etiology of stenoses, occlusions or perivascular structures. Angioscopy, another intravascular imaging tool, allows direct visualization of the vessel lumen but provides no cross-sectional information and is inundated with technical difficulties. Table 1 summarizes the three intravascular imaging modalities. Intraobserver and interobserver variations also may tend to make angiographic interpretation less accurate (Table 2).3, 12