Introduction
Congenital heart disease (CHD), with an estimated incidence rate of 1%
of newborns, remains to be the most common congenital malformations
leading to high morbidity and mortality of neonates [1-3].
Echocardiography is the most effective modality to diagnose CHDs
prenatally, which assures proper perinatal management and thus improves
the outcome. Theoretically, most CHDs could be detected in the uterus by
an experienced fetal echocardiographer [4]. They are sensitive to
find subtle changes in morphology and hemodynamics in fetal heart and to
trace the clues to make an accurate diagnosis [5]. However, this
beyond the ability of most screening sonographers as it needs much
experience and expertise. A systematic scanning procedure with standard
cardiac planes is in need.
As recommended by ISUOG guidelines for fetal echocardiography, a series
of transverse planes is proposed in routine cardiac scans, including the
four-chamber view (4CV), bilateral outflow tracts views, and the
three-vessel trachea (3VT) view [6]. Previous reports had suggested
a high efficacy in detecting fetal CHDs using these transverse planes
[7-10]. However, some abnormalities in the fetal upper mediastinum
are apt to be missed by routine cardiac screenings. It is possible to
improve the detection of fetal CHDs by including more transverse cardiac
planes in addition to the existing recommended views.
Fetal great vessels could be visualized directly by gray-scale
ultrasonography. Color Doppler could undoubtedly enhance morphological
information and determine the blood direction. High-definition flow
(HD-flow) imaging is a special bidirectional Doppler technique that has
the potential benefits of better axial and lateral resolution, fewer
blooming artifacts, and improved sensitivity to display vessel perfusion
and blood flow continuity than traditional Color Doppler [11-13].
Recently, the use of radiant flow (R-flow) imaging technique is a great
improvement in fetal cardiac imaging. By specific algorithm, the index
of erythrocyte density in a certain area is converted into height index
and then superimposed on the initial coding of color or HD-flow. The
flow is then displayed in a sense of depth, resembling a
three-dimensional visual effect. Besides, the use of Color
Doppler/HD-flow together with the R-flow technique could apparently
reduce color overflow and thus show vessels with sharp edges.
The current study aimed to evaluate the efficacy of a detailed procedure
exploring vessels in the fetal upper mediastinum. Two color imaging
modalities were used to compare their performance in the investigation
of these planes.