o_1977r8vv9vk1ts2ms0kd8pksa.pdf

466 D. Maulik
Fig. 32.1. Factors affecting the quality of diagnostic information
derived from fetal cardiac imaging
graphic information, but the utility of a device significantly
depends on the skill of the operator in generating
the diagnostic information and the skill of the
diagnostician in interpreting that information. For
reliable and confident fetal echocardiographic assessment,
it is crucial to ensure not only the adequacy of
the instrumentation but also the sufficiency of training
and skill of the provider.
Ultrasound System
The basic principles of duplex pulsed-wave Doppler
and color flow Doppler instrumentation have been
described in Chaps. 3 and 6. Here the relevant issues
specifically related to fetal echocardiographic application
are briefly discussed. The desirable configuration
of an ultrasound device for fetal echocardiographic
examination consists of a multiplex system. Several
ultrasound modalities comprise such a system, including
high-quality 2D imaging and other sonographic
techniques. These devices enable the sonographer
to perform with reasonable confidence comprehensive
structural and functional assessments of
the fetal heart. When choosing a device, critical consideration
should be given to the quality of the resolution
of 2D imaging and the transducer features
appropriate for the needs of fetal echocardiographic
examination. As with any other field of medical ultrasound
imaging, an appropriate archival system is selected
so images and reports can be saved and retrieved
in a reliable manner.
Integration of 2D imaging with Doppler sonography
offers some unique challenges, and the various
approaches to their solution are reflected in the device's
features. For example, high-resolution imaging
requires a high-frequency transducer; in contrast,
Doppler signals are weaker than the pulse echocardiographic
specular reflections of imaging and require
a low-frequency transducer for optimal sensitivity.
The introduction of multifrequency transducers
offers an innovative solution, as higher imaging resolution
can be achieved at higher frequency, whereas
Doppler sensitivity is improved using a lower frequency.
Because of the angle dependence of Doppler
signals, the optimal imaging plane is often not consistent
with the optimal Doppler plane. Beam steering
capability of the array transducers may assist in these
circumstances. Careful consideration of these factors
helps the operator select the appropriate device for fetal
echocardiographic application.
The choice of transducer frequencies appropriate
for fetal echocardiographic examination should be individualized
to achieve the best possible resolution
for a given depth of the scanning target. The higher
the frequency of the incident beam, the greater the
spatial (axial) resolution and the lower the depth of
penetration. Depending on the maternal habitus, gestational
age, and fetal position, the fetal heart often
lies deep from the maternal abdominal surface.
Although a 5-MHz transducer produces a higher resolution
image of the fetal heart, it may not be able to
reach such depth. In this circumstance, a 3-MHz
transducer may be necessary. As mentioned previously,
multifrequency transducers offer a convenient
solution.
Consideration should also be given to the type of
transducer appropriate for fetal cardiac evaluation
(discussed in detail in Chaps. 3 and 6). It is generally
recognized that electronic-array design offers significant
advantages. Both convex sequential-array and
phased-array transducers may be used for fetal echocardiographic
applications. For most obstetric applications,
including fetal cardiac evaluation, convex sequential
transducers are often preferred, as they provide
uniform high resolution in the image plane.
However, phased-array devices may be helpful when
fetal orientation limits acoustic access to the fetal
heart.
Preparation for Echocardiographic
Examination
It is imperative that the mother be informed prior to
examination in a clear and considerate manner about
the reason for fetal cardiac evaluation, as well as
about the procedure, efficacy, and limitations of fetal
echocardiography. The findings should be explained
at the conclusion of the examination. The family may
participate in this session at the mother's discretion.
The overall approach should be multidisciplinary, involving
the obstetrician, maternal-fetal medicine specialist,
pediatric cardiologist, and neonatologist. The
counseling procedure should be documented.
The examination is performed with the patient
lying in a semirecumbent left lateral position on a
comfortable, secure examination table. The examination
often must be conducted with the mother in the
supine position, in which case care is taken to limit
the duration of the procedure to avoid supine hypo-