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Chapter 6
Sonographic Color Flow Mapping: Basic Principles
Dev Maulik
Color flow mapping consists of real-time depiction of
two-dimensional flow patterns superimposed on
cross-sectional pulse echo images of anatomic structures
[1±3]. The flow patterns are color-coded to present
a variety of hemodynamic information. Doppler
color flow mapping is based on the estimation of
mean Doppler-shifted frequency and does not provide
information on peak frequency shift or actual
flow. Furthermore, the hemodynamic information
provided is qualitative rather than quantitative.
Nevertheless, color flow mapping has proved useful
for elucidating structural and functional abnormalities
of the circulatory system. The technique was first
introduced in cardiology practice and has revolutionized
noninvasive diagnosis of cardiac pathology. The
use of this method has since been extended to other
medical disciplines. In obstetrics and gynecology,
color flow mapping has been used to investigate fetal
and maternal hemodynamics during pregnancy and
pelvic vessels in non-pregnant women. Color flow has
been found to be useful for elucidating complex cardiac
malformations of the fetus, directing spectral
Doppler interrogation of fetal cerebral, renal, and
other circulations, diagnosing ectopic pregnancy, and
assessing pelvic tumor vascularity. It should be recognized,
however, that the information generated by
Doppler color flow mapping is significantly influenced
by the instrumental setting and characteristics.
The reliability of the method thus depends on the appropriate
use of the device by the operator, who
should have a clear understanding of the basic principles
of Doppler color flow mapping and its implementation.
In this chapter we describe the basic principles,
instrumentation, and limitations of Doppler color
flow mapping and present practical guidelines for its
use. We also discuss an alternative sonographic color
flow mapping technique based on the time domain
processing analysis.
Principles of Doppler Color
Flow Mapping
Multigated Doppler Interrogation
Doppler color flow mapping is based on multigated
sampling of multiple scan lines using bursts of short
pulses of ultrasound (Fig. 6.1). Many range-gated
samples are obtained for each emitted pulse of ultrasound
along a single scan line by opening the receiving
gate sequentially to the echo signals arriving from
various depths along the scan line. The time needed
for the return journey of the echo is used to determine
the spatial origin of the returning echoes. Assuming
a sound propagation speed of 1,540 m/s in
tissue, the echo return time for an emitted sound
pulse in 13 ms/cm of tissue depth. Thus a signal from
a depth of 5 cm takes 65 ms from the moment of
transmission to its return to the transducer. If the
second sample is to be obtained from a depth of
10 cm, the range gate is opened at 65 ms after reception
of the first sample (130 ms after transmission of
the pulse). In reality, many samples are collected, and
the consecutive sampling of the signals along the
Fig. 6.1. Doppler color flow mapping. Multigated sampling
of multiple scan lines sweeping across the field of color
Doppler interrogation