Standardized views of the fetal heart using four‐dimensional sonographic and tomographic imaging

Abstract

A growing body of evidence indicates that three-dimensional (3D) and four-dimensional (4D) ultrasound imaging with spatiotemporal image correlation (STIC) facilitate the examination of the fetal heart.1-46 Thus, 3D and 4D fetal echocardiography have the potential to reduce the operator dependency of two-dimensional ultrasonography and may increase the detection rate of congenital heart defects (CHDs). Tomographic ultrasound imaging (TUI) has been introduced recently as a new display modality for 3D and 4D ultrasonography. This approach allows the simultaneous display of multiple parallel sonographic planes. An “overview image” is shown in the upper left corner on which parallel lines demarcate the position of the slices orthogonal to this overview image (Figure 1). Other commercially available software with similar capabilities include Multi-Slice View™, i-Slice and MultiSlice Imaging. Figure 1 An “overview image” is shown on the upper left corner. The parallel lines determine the position of the eight orthogonal planes to the plane containing the “overview image.” Volume datasets obtained with 3D and 4D sonography can be compared to blocks of pathological specimens where all the anatomical information is contained in the block and the information displayed depends on the level at which the block is cut. Using this analogy, the overview image in TUI indicates the position at which the slices are cut. The user can adjust the number and position of slices with specific software controls. TUI has been used for the examination of the fetal heart47-49 and other fetal organs.50-53 However, the untargeted use of TUI for the examination of 4D volume datasets from the fetal heart provides images with and without diagnostic value. In order to determine the minimum number of images required for a comprehensive examination of the fetal heart we developed an algorithm using TUI and STIC.49 This algorithm allows the simultaneous visualization of the standard planes for fetal echocardiography including the four-chamber view, three-vessel view, left outflow tract and short axis (right outflow tract), in most fetuses without CHDs.49 In this article, we describe a practical approach for the examination of the fetal heart using this algorithm. Volume Acquisition This technical paper includes images from fetuses with and without CHDs, confirmed postnatally by echocardiography, surgery or during autopsy. 4D ultrasounography of the fetal heart was performed using the STIC technique (Voluson 730 Expert, release BTO4, GE Healthcare, Milwaukee, WI, USA) using hybrid mechanical and curved array transducers (RAB 4-8P, RAB 4-8L, RAB 2-5P, RAB 2-5L). 4D volume datasets of the fetal heart were acquired with transverse sweeps through the fetal chest. Acquisition time ranged from 7.5 s to 15 s and the angle of acquisition ranged between 20° and 40° depending on fetal motion and gestational age. The algorithm can be applied to both volume datasets acquired with B-mode imaging and color Doppler ultrasonography. However, color Doppler imaging may improve the visualization rates of the three-vessel and trachea view, as well as the simultaneous visualization of the three-vessel and trachea view, the four-chamber view and both outflow tracts.49 Image quality depends on the following factors during volume acquisition: 1) the fetal spine should be positioned between three and nine o'clock in order to minimize shadowing from the ribs or spine; 2) minimal or no maternal and fetal motion; and 3) the volume dataset should include the upper fetal mediastinum. 3D/4D ultrasound studies were conducted under protocols approved by the institutional review boards of both Wayne State University and the National Institute of Child Health and Human Development (NICHD/NIH/DHHA). All patients gave written informed consistent before participating in the study.