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.