o_1977r8vv9vk1ts2ms0kd8pksa.pdf

570 I. Zalud
and pulsed-wave Doppler gain, color gate, sample volume,
and wall filter must also be adjusted. Automatic
default settings can be used to speed up the examination.
However, manual adjustments of all mentioned
parameters are needed to detect and differentiale lowvelocity
and high-velocity vessels. If inadequate Doppler
settings are used, low-velocity vessels might not
be visualized at all and high-velocity vessels might
exhibit an artifact known as aliasing. Unfortunately,
there are no universal guidelines for Doppler studies
in gynecology, one reason being the large variety of
Doppler ultrasound instruments that use different
technical setups for blood flow visualization and measurement.
Another more unfortunate reason is the
lack of standardization of Doppler measurements.
The setups are often not mentioned in the literature,
making comparisons of studies impossible. Reports
of these studies with precise information about the
Doppler settings are rare. Moreover, the results reported
vary widely and are sometimes controversial,
which may ultimately compromise and devalue this
relatively new ultrasound technique. Standardization
of Doppler measurements is urgently needed.
Color flow can be quantified by pulsed-wave Doppler
waveform analysis. The peak systolic (A) and
end-diastolic (B) Doppler shift frequency can be recorded;
and the A/B ratio, Pourcelot resistance index
(RI), the pulsatility index (PI), and other indices may
be calculated. The RI is a useful way of expressing
blood flow impedance distal to the point of sampling.
Each parameter is angle-dependent, but once they are
in proper relation the RI becomes independent of the
angle between the investigated vessels and the emitted
ultrasound beam. Although the volume flow measurement
would be of more benefit than Doppler waveform
analysis, this approach requires precise measurement
of the angle of insonation and the diameter
of the vessel. If achieved, the volume (milliliters) of
blood passing through a certain vessel during a particular
time unit can be calculated. To avoid these
measurement difficulties, waveform analysis offers
semiquantizative assessment of the quality of blood
flow. Because the systolic and diastolic blood flows
are expressed as a ratio, measuring one or the other
of these blood flows is not sufficient to report it as
high-velocity or low-velocity flow: The flows cannot
be observed and interpreted separately. This point is
particularly important for randomly dispersed small
vessels, for which the angle of insonation and the diameter
of the vessel are almost impossible to determine.
The basic question is whether the color signal
represents a single small vessel or it is a summary of
flow from an unknown number of small vessels. It is
believed that the increased RI value results from increased
peripheral vascular resistance. For each measurement,
at least three cardiac cycles must be recorded
and the mean value of the RI calculated. The
mean duration of examination is usually no longer
than 15 min in experienced hands. The spatial peak
temporal average intensity should not exceed
100 mW/cm 2 , which is the highest limit of insonation
energy permitted by the US Food and Drug Administration
(FDA) for use in fetal medicine.
Normal Pelvic Blood Flow
Transvaginal color Doppler (TVCD) sonography and
pulsed-wave Doppler sonography provide a unique
noninvasive method for the evaluation of normal and
abnormal conditions in the female pelvis [1]. Transvaginal
ultrasonography displays uterine, iliac, and
ovarian blood flow in pregnant and nongravid women
and identifies physiologic flow patterns. Blood
flow in the main pelvic vessels can be easily visualized
and recognized. The artery and vein are distinguished
according to the pulsation and brightness of
color flow (Fig. 39.1). The internal iliac vessels can be
visualized in the entire population. The iliac vein is
most commonly seen immediately below the ovary.
The ability to view iliac veins is an excellent way to
document patency or thrombosis. The iliac arteries at
the bifurcation have characteristic waveforms. The
common and external iliac arteries, which are part of
the aortofemoral segment, show plug flow, a window
under the waveform, and a reversed component during
diastole. The internal iliac artery, in contrast, has
parabolic flow with an even distribution of velocities
within the waveform. Internal iliac vessels can usually
be observed in the side wall of the pelvis, often lying
deep and close to the ovary. The internal iliac artery
produces prominent, pulsating color flow at high velocity,
typically with reverse flow and high impedance
of flow.
Fig. 39.1. The internal iliac artery (red) and vein (blue) are
distinguished by color Doppler according to the brightness
of the color and pulsation, not by the color itself