o_1977r8vv9vk1ts2ms0kd8pksa.pdf

474 D. Maulik
technique, multigated Doppler sampling is performed
on a single scan line, which is sampled 1,000 times a
second, and the unidimensional tissue and color flow
images are scrolled (usually from right to left on the
video screen) and therefore displayed as a function of
time. Because of the high sampling rate from a single
line, the color M-mode technique provides a high
Doppler sonographic sensitivity and temporal resolution
and allows reliable timing of the flow with the
events of the cardiac cycle. For these reasons, color
M-mode sonographic technique is useful for fetal
echocardiographic examination.
Tissue Doppler Echocardiography
Tissue Doppler sonography comprises processing and
analyzing Doppler frequency shift generated by tissue
movement. The physical and technical principles of
tissue Doppler imaging of the heart are similar to
those of Doppler sonography of blood flow with the
exception of the approach to filtering. Doppler insonation
of the heart generates signals from cardiac
blood flow and myocardial movement. However, the
Doppler signals generated by blood flow are of substantially
lower amplitude and higher frequency than
those from myocardial movement. In depicting flow,
the high-pass filter system eliminates the high-amplitude
and low-frequency myocardial Doppler signals
so that only flow signals are displayed. In contrast,
tissue Doppler echocardiography utilizes filtering that
eliminates the low-amplitude high-frequency flow signals
permitting tissue Doppler signals being displayed
(Fig. 32.17). There are three types of tissue Doppler:
pulse-wave tissue Doppler mode, color flow tissue
Doppler mode, and color tissue Doppler M-mode.
In the adult, tissue Doppler echocardiography has
been used for assessing cardiac systolic and diastolic
functions [20±22]. Such assessments can be performed
by measuring myocardial velocity, myocardial
velocity gradient, myocardial strain, and strain rate.
Myocardial strain is its deformation during systole
and diastole. Strain implies differential velocities in
the cardiac wall and does not reflect overall movement
of the heart including its translational motion
within the thorax in relation to the other structures.
Detailed reviews of these concepts may be found elsewhere
[23].
More recently the feasibility of tissue Doppler
sonography for fetal cardiac assessment has been
reported. Harada and associates measured motion
Fig. 32.17. Tissue Doppler velocity waveforms from the right
ventricular wall below the parietal insertion of the tricuspid
valve. The sampling site is indicated by the horizontal arrow
pointing to the Doppler sample volume (two horizontal lines).
The diastolic and systolic velocity waveforms are indicated on
the lower panel. A indicates arterial systole and E indicates
end diastole. RA right atrium, LA left atrium, MV mitral valve,
TV tricuspid valve, RV right ventricle, LV left ventricle