o_1977r8vv9vk1ts2ms0kd8pksa.pdf

472 D. Maulik
short interval during which spectra are interpolated;
and (3) time-sharing algorithms that produce simultaneous
display of spectral Doppler images and 2D
images by sharing the available pulses during a given
time interval between the two modes. Unfortunately,
all of these approaches have trade-offs and therefore
do not provide an ideal solution.
Finally, duplex pulsed-wave Doppler ultrasonography
can be used to determine fetal cardiac output.
The principle of this technique is briefly described
later in the chapter.
Fig. 32.14. Two-dimensional echocardiogram of the fetal
heart depicting the aortic arch. Note the tight curvature of
the aortic arch and the origin of the arteries supplying the
head and neck. Compare it with the curvature of the ductal
arch shown in Fig. 32.12. LV left ventricle, AA aortic arch, rp
right pulmonary artery, S fetal spine, DA descending aorta
tion, repeated verification of the location of the Doppler
sample volume is essential. Various approaches
may be used, including (1) display of a frozen 2D image
that is updated at predetermined intervals, verifying
the Doppler sample volume location; (2) interpolation
techniques that produce a 2D image during a
Color Doppler Flow Mapping
The introduction of color Doppler echocardiographic
technique represents one of the major advances in
noninvasive cardiac diagnosis [17, 18]. Fetal cardiac
hemodynamics have been imaged using the color
mapping technique [19]. The depiction of Doppler
mean frequency shifts by 2D flow mapping requires a
balanced compromise between spatial resolution,
Doppler accuracy, and temporal resolution. The normal
range of the fetal cardiac cycle in 0.375±0.545 s
(corresponding to a heart rate of 120±160 bpm). This
degree of rapidity of fetal cardiac events necessitates
an adequate processing speed to maintain temporal
resolution. The small size and deep location of the fetal
heart and the inability to ensure its favorable orientation
impose further restrictions on obtaining
adequate signals.
With Doppler color flow mapping for a given sector
size, the more numerous the scan lines, the better
the spatial resolution of the color (see Chap. 6).
Furthermore, the more profuse the samples per scan
line, the more accurate the mean velocity estimation.
However, increasing the scan lines and sample points
Fig. 32.15. Spectral Doppler interrogation.
Left panel: Pulmonary outflow. The
Doppler path is indicated by the cursor
line. The Doppler sample volume (horizontal
lines) is placed in the outflow
tract. Right panel: Spectral Doppler waveforms
from the ductus. As the flow is
towards the transducer, the waveforms
deflect upward from the baseline