16

Factors Affecting Color Flow Images: The Creation of the Color Flow Image

The majority of the CFI systems in operation today use Doppler techniques to determine color velocity estimates. Color flow imaging is significantly different from PW Doppler in the way it gathers and processes information.

PW Doppler displays the complete spectrum of blood flow velocities present at one sample site (the sample volume) on one scan line. Conversely, color flow imaging displays one blood flow value, the mean velocity, at each of several hundred sample sites along many different scan lines

The number of sample sites per color scan line varies among manufacturers, while the number of color scan lines interrogated is determined by the color sector width and the color line density. In addition, each scan line is sampled a number of times determined by the packet size you select. The result is a very large number of sample sites, each containing a relatively small number of Doppler data points. To efficiently acquire and process this amount of blood flow data, ultrasound systems use color algorithms. Each time a color scan line is interrogated for color information, the algorithm stores one Doppler data point at each sample site on the line. For example, if the packet size is eight, there are eight Doppler data points at each sample site.

The algorithm processes these data points and derives a mean velocity estimate for each sample site. Based on this mean velocity estimate, the algorithm assigns a color to each site.