3D ultrasound is a medical ultrasound technique, often used in obstetric ultrasonography (during pregnancy), providing three-dimensional images of the fetus. Three-dimensional ultrasound, also known as phased array ultrasonics, is used extensively in the non-destructive evaluation of materials for purity and failure assessment.
There are several different scanning modes in medical and obstetric ultrasound. 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 sophisticated computer program resulting in a reconstructed three-dimensional volume image of the 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.
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.