ABSTRACT
In B-flow imaging the echoes from moving tissues are enhanced. Non-moving regions of blood or tissue are displayed as dark, and regions where the velocity is high are displayed bright. When viewed in real time, or in video format, an impression of flow is obtained. The B-flow method is based on a pair of coded pulses, one pulse the complement of the other. Conventional spectral Doppler and colour Doppler systems all suffer from angle dependence, in that the detected Doppler frequency shift is dependent on the angle between the beam and the direction of motion. Commercial implementation of vector flow techniques has been achieved using a technique called ‘transverse oscillation’. Consider velocity estimation by the Doppler effect; this relies on creation of an oscillation at the transmit frequency in the direction of the ultrasound beam. One of the main issues for conventional colour flow systems is achieving real-time frame rates.
