Color coded Doppler flow mapping

Abstract

Color coded Doppler flow mapping (color flow mapping or color Doppler) is a newly developed technology which displays blood flow as color-coded information on the two-dimensional image. This method is an application of the pulsed Doppler method. The conventional FFT analysis takes too much time to analyze the blood flow information for color flow mapping. Moving target indication and autocorrelation methods are employed to process the spatial flow information in real time. In these methods, the pulses are transmitted several times in the same direction along a certain scan line for data processing. When the echo comes from a stationary target, the delay time from the transmission and reference signals is constant each time, while it varies when the target moves (Figure 11.1). The number of transmitted pulses in the same direction is called the ’packet size’, which must contain at least three pulses for velocity evaluation. After obtaining data for one color scan line, the beam is steered to the next color scan line. To improve the color quality (velocity verification), it is necessary to enhance the autocorrelation by increasing the packet size. The packet size also affects the color frame rate: the larger the packet size, the lower the frame rate. The color frame rate is also affected by the number of the color scan lines related to the color angle of the sector: the wider the color angle, the lower the frame rate. A low frame rate can sometimes lose real time information about blood flow, especially in patients with higher heart rates. Therefore, the small packet size and narrower angle color presentation is required in such cases.