3-DIMENSIONAL FETAL ECHOCARDIOGRAPHY - GATED VERSUS NONGATED TECHNIQUES

The purpose of this study was to compare gated with nongated three-dim ensional fetal echocardiography in terms of the ability to demonstrate fetal cardiac anatomy. We examined nine fetuses in utero using conven tional two-dimensional sonographic imaging equipment, an electromagnet ic position sensor, and a computer-graphics workstation. Free-hand swe eps were performed through the fetal heart and great vessels in either transverse or sagittal orientations with respect to the fetal heart. Seven transverse and five sagittal sweeps were selected for reconstruc tion and analysis. Cardiac gating was performed by using a temporal Fo urier transform to determine the fundamental frequency of cardiac moti on. Two-dimensional data from each sweep were reprojected to a series of volume data sets. Each series was then condensed to a single volume , so that each two-dimensional sweep could be compared with its respec tive gated and nongated volume data sets. The two-dimensional data wer e reviewed utilizing a display with forward and backward cineloop capa bility. The gated and nongated volume data sets were displayed interac tively as a series of three orthogonal planes, with the ability of the observer to control the location of each image plane within the volum e. The gated data were animated with variable display frame rates. Con ventional two-dimensional imaging provided a fairly complete evaluatio n of the fetal heart when scanning included the few-chamber view with a sweep across the outflow tracts. Nongated three-dimensional fetal ec hocardiography allowed visualization of some structures and views not demonstrated with hue-dimensional ultrasonography. Gated three-dimensi onal fetal echocardiography provided significantly better visualizatio n and comprehension of cardiac anatomy than nongated three-dimensional fetal echocardiography. The superiority of gated over nongated three- dimensional fetal echocardiography appears to come from both improved image quality and the anatomic clues that derive from the ability to v iew cardiac motion.