Fetal cardiac evaluation by 3D/4D ultrasonography

The congenital heart disease are the most common major malformation at birth.  In 2003, with the development of Spatio-Temporal Image Correlation (STIC), scientists started the use of third and fourth dimension ultrasonography (3D/4D) in fetal cardiac evaluation. The STIC is a software that enables acquiring volumetric fetal heart with  its vascular connection, whose images can be evaluated  either multiplanar or rendering modes, or even surface mode, in a static or moving ways (4D) by means of cineloop, which simulates a complete cardiac cycle.Thus, a detailed assesment of the anatomy and the functioning fetal heart is possible without the need to cause major discomfort to pregnant  women.

Standarization of volume storage is already a reality. so the investigator has knowledge of the actual position of the heart chambers with respect to the right and left fetal axis to evaluate the presence of possible cardiac isomerism. Therefore,  when the fetus is in cephalic presentation, it should be considered that the heart side corresponds to the fetal side, unlike the pelvic fetuses which stay in opposite sides.

The gray scale and color Doppler applications are also present in the STIC, used to improve the evaluation of the ventricular outflow tracts, aortic and ductal arches, besides assisting in the location of septal defect. The 3D technology has allowed the development of new techniques known as inversion mode (analysis technique of liquid  structure which reverses voxels of gray scale, so anechoic structures such as the heart chambers and lumen vessels, with inversion mode they become echogenic and B-flow imaging (technique that improves the weak signal reflected from the blood, and supresses the strong signals of the surrounding structures). The inversion mode allows the reconstructionof the cardiac chambers, aortic and ductal arches, and abnormalities of venous connection. The B-flow imaging shows high sensitivity and angle independence, then it is potentially advantageous over colour Doppler for the visualization of large vessels and venous return, allowing the identification of small vessels with low-velocity flows, such as pulmonary veins, enhancing the detection of anomalies in pulmonary venous return.

Another technique also addressed by STIC Tomographic Ultrasound Imaging's (TUI), which enables the achievement of all the axial planes of the heart from the abdoment to the apex of the chest, increasing the fetal heart tracking and analysis. STIC also allows the measurement of volume cardiac chambers, as well as the calculation of systolic volume, ejection fraction and cardiac output. Thus, to obtain relevant information about cardiac function due to the congenital heart disease. More recently, a new approach to STIC rendering mode analysis obtained measurements of mitral and tricuspid valves areas, and also the interventricular septum, determining reference values for these parameters, making it feasible to apply in suspected or pathological cases.