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Chapter 34
Four-Dimensional B-Mode
and Color Doppler Echocardiography
of the Human Fetus
Dev Maulik
Introduction
Sonographic imaging of the fetal heart remains technically
challenging because of the complexities of fetal
cardiac structure and function, the dependence of
the acoustic access on fetal position and fetal movement.
The technique is highly dependent on the operator's
skill, requires intense training, and has a steep
learning curve. While performing two-dimensional
(2D) echocardiography, the operator conceptually recreates
the spatial three-dimensional (3D) reality of
the fetal heart out of the 2D sonographic images.
Although this approach continues to function well,
the advantages of four-dimensional (4D) echocardiography,
which is 3D imaging in real time, are potentially
immense. Three-dimensional images can be created
by postprocessing of the digital graphic information
generated by sequential 2D imaging; however,
when 3D imaging is performed in real time it constitutes
4D imaging. For echocardiography this translates
into instantaneous display of the spatial and
temporal reality of the heart as the operator performs
the scanning. Although the potential of 3D or 4D
echocardiography has been appreciated for more than
two decades, the actual development of this modality
has to overcome significant engineering and computational
challenges. Not surprisingly, the early 3D
methods did not possess the capability of imaging
the fetal heart in real time with acceptable temporal
or spatial resolution; however, recent remarkable
technological breakthroughs have led to the commercial
introduction of true 4D echocardiography instrumentation
in adult and pediatric cardiology and have
raised the prospect of extending these newer techniques
for fetal cardiac assessment. This chapter
briefly reviews these recent developments in this field
with emphasis on the Doppler mode.
History of Four-Dimensional
Echocardiography
The origins of 3D medical imaging can be traced
back three decades with the advances of computed
tomography and magnetic resonance imaging. Essentially,
the tomographic image slices generated by
these modalities are digitally reconstructed to produce
3D images. These developments have revolutionized
medical imaging and diagnostics. Even with the
continuing advances in technology, these modalities,
however, cannot match the versatility of ultrasound
for imaging the heart. The development of 3D echocardiography
began in the 1970s and 1980s. Pioneering
groups of investigators, including Dekker and associates
[1], Ghosh and colleagues [2], and others
[3], utilized various experimental approaches, which
essentially consisted of offline reconstruction of 2D
images. Subsequent research and development eventually
led to the clinical introduction of systems that
utilized offline 3D reconstruction from multiplanar
2D images obtained via transthoracic or transesophageal
routes by a rotational method or parallel scanning
[4]. A recent remarkable technological accomplishment
in this field was the development of matrix
phased array which allowed true real-time 4D imaging,
introduced first by von Ramm and associates [5]
and is discussed later in this chapter.
Regarding the feasibility of 3D fetal echocardiography,
initial investigations mostly consisted of 3D reconstruction
of sequential 2D images acquired either
by free hand scanning combined with position sensors,
or by motorized scanning with a one-dimensional
linear-transducer array [6]. These approaches
did not perform strictly 4D imaging and some form
of cardiac gating was necessary to make any sense of
the images. Another approach used two ultrasound
devices concurrently with one generating 2D grayscale
and color Doppler images with 3D spatial movement
tracking, whereas the other used umbilical arterial
Doppler velocimetry to provide cardiac gating
[7]. These laudable pioneering efforts depended on
substantial postprocessing to generate the volume
data set, were often cumbersome, and suffered from
many limitations including poor spatial and temporal
resolution.
Subsequent advances have addressed many of these
limitations leading to the development of the two distinct
current systems; one is based on the recently introduced
second-generation matrix 2D phased-array
system and represents a significant breakthrough in