ABSTRACT
The development of colour flow imaging has led to an increase in the investigation of blood flow to aid diagnosis of both vascular and non-vascular disorders. An understanding of the physical properties of blood flow is essential when interpreting colour flow images and Doppler spectra. The structure of the arterial wall can change due to disease and these changes may be observed using ultrasound. Artery walls consist of a three-layer structure. The inner layer, the intima, is a thin layer of endothelium overlying an elastic membrane. The middle layer, the media, consists of smooth muscle and elastic tissue. The outer layer, the adventitia, is predominantly composed of connective tissue with collagen and elastic tissue. The flow in normal arteries at rest is laminar. This means that the blood moves in layers, with one layer sliding over the other. These layers are able to move at different velocities, with the blood cells remaining within their layers.
