3D ultrasound is a medical ultrasound technique, often used in obstetric ultrasonography (during pregnancy), providing three dimensional images of the fetus. The standard common obstetric diagnostic mode is 2D scanning. In 3D fetal scanning, however, instead of the sound waves being sent straight down and reflected back, they are sent at different angles. The returning echoes are processed by a so
phisticated computer program resulting in a reconstructed three dimensional volume image of fetus's surface or internal organs, in much the same way as a CT scan machine constructs a CT scan image from multiple x-rays. 3D ultrasounds allow one to see width, height and depth of images in much the same way as 3D movies but no movement is shown.
3D ultrasound was first developed by Olaf von Ramm and Stephen Smith at Duke University in 1987. Clinical use of this technology is an area of intense research activity especially in fetal anomaly scanning but there are also popular uses that have been shown to improve fetal-maternal bonding. 4D fetal ultrasounds are similar to 3D scans, with the difference associated with time: 4D allows a 3-dimensional picture in real time, rather than delayed, due to the lag associated with the computer constructed image, as in classic 3-dimensional ultrasound. If the system is used only in the Obstetrics Application, the ultrasound energy is limited by the manufacturer below FDA limits for obstetrical ultrasound, whether scanning 2, 3 or 4 dimensionally. (The FDA limit for obstetrical ultrasound is 94 mW/cm2.) While there has been no conclusive evidence for harmful effects of 3D ultrasounds on a developing fetus, there still remains controversy over its use in non-medical situations, and generally, the AIUM recommends that 3D ultrasounds should be undertaken with the understanding that a risk may exist
