Objective: This study defines the spatial relationship of the diagnostic planes of the fetal heart to the 4-chamber view plane in the second trimester of pregnancy as a first step in the automation process.
Methods: Three-dimensional static volumes of the fetal chest were acquired at the level of the 4-chamber view on 75 fetuses between 18 and 23 weeks' gestation. The spatial relationship of the diagnostic cardiac planes to the 4-chamber view plane were determined for each gestational week by using rotations along the x-, y-, and z-axes and a parallel slide (millimeters) when applicable.
Results: The 5-chamber view (cardiac 1 plane) was best obtained by an initial parallel slide of the reference plane (plane A) toward the fetal head followed by a rotation along the y-axis. The right ventricular outflow tract (cardiac 2) and the abdominal circumference (cardiac 3) planes were best obtained by a parallel slide only: toward the fetal head in cardiac 2 and toward the fetal abdomen in cardiac 3.
Conclusions: This study shows the spatial relationship of fetal cardiac diagnostic planes to the 4-chamber view plane in the second trimester of pregnancy in 3-dimensional volumes. Testing the clinical applicability of automated software based on these formulas is the next step.