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a Chapter 6 Sonographic Color Flow Mapping: Basic Principles 71
Table 6.1. Ultrasound modalities in current diagnostic devices
Two-dimensional real-time gray scale imaging
M-mode
Spectral Doppler
Doppler color flow mapping
Color flow M-mode
Doppler color flow amplitude (power or energy) mode
Instrumentation
Fig. 6.3. Principle of two-dimensional Doppler signal analysis.
During the first ultrasound transmission, the stationary
tissue objects and the moving erythrocytes generated
echoes (A1 and B1, respectively). During the second transmission
echoes are produced again (A2 and B2, respectively).
Note that the echoes from the stationary objects remain
the same (A1 and A2), whereas those originating
from the moving objects (B1 and B2) differ. Correlating the
first echo with the next echo cancels the signals from the
stationary targets and identifies the signals from the moving
scatterers (C). This process is repeated with the successive
echoes from moving targets to estimate the mean
Doppler frequency shift in real time
where ' is the phase angle, MF d is the mean Doppler
frequency shift, and PRF is the pulse repetition frequency.
The autocorrelation is achieved by electronically
delaying an echo signal, which is then processed
with the subsequent echo signal (see above).
The instrumentation for two-dimensional Doppler
color mapping consists of multiplex systems that
combine multiple ultrasound modalities, providing a
comprehensive array of sophisticated diagnostic tools
(Table 6.1). It is not surprising that the technology
employed in these devices is highly complex, especially
in the Doppler color mode. In addition, commercially
available devices not only demonstrate a
fair degree of diversity in the engineering implementation
of the Doppler technology they also differ in
the organization and the choice of system controls
they offer to the operator. Although a comprehensive
discussion is beyond the scope of this chapter, we
present here the basic principles of Doppler color
flow instrumentation.
Color Flow Processor
The basic components of a color flow signal processing
system consist of the following (Fig. 6.4):
Fig. 6.4. Doppler color flow signal
processing system