Diagnostic Ultrasound: Colour flow and tissue imaging

Introduction Doppler ultrasound remained a minority imaging methodology until the introduction of colour Doppler in 1982. In this technique, the motion of the blood is colour-coded and superimposed on the B-mode image. This allows rapid visualization of the flow patterns in vessels, allowing high-velocity jets in arteries and in cardiac chambers to be seen. It quickly became apparent that the ability to visualize flow patterns, such as the presence of intracardiac jets, was of great value. In addition, it considerably speeded up the placement of the Doppler sample volume in spectral Doppler investigation, hence reducing scanning time. Prior to the introduction of commercial colour flow systems, several approaches were described to provide an image showing the pattern of blood flow. These often relied on manual scanning of the probe over the skin to build up a two-dimensional (2D) image. These systems, which used electronic or mechanical sweeping of the beam, were not real-time, having only a maximum of a few frames per second. These are reviewed in Evans and McDicken (2000),Wells (1994) and Cobbold (2007). This chapter also includes a description of ‘B-flow’ imaging in which the B-mode image is modified to enhance the visibility of blood, and Doppler tissue imaging in which colour-coding of motion is applied to tissues such as the myocardium.