This chapter concentrates on computational simulation based on magnetic resonance imaging (MRI) and ultrasound imaging. It explores the flow structure and wall shear stress distributions, and describes the relationship with arterial disease patterns. An accurate description of 3D vessel geometry is essential for accurate modelling of blood flow using computational fluid dynamics (CFD), and magnetic resonance angiography (MRA) has been the most popular technique for obtaining the information in vivo. However, for superficial vessels such as the carotid and femoral arteries, extravascular 3D ultrasound can be a cost-effective alternative to MRA. Extravascular 3D ultrasound has potential to become a relatively inexpensive, fast and accurate alternative to MRI for CFD-based hemodynamics studies of superficial arteries. Standardized imaging protocols with high quality images will certainly help to reduce the manpower needed for model reconstruction and preparation, and to minimize operator dependence of the reconstruction process.