3D ultrasound is a medical ultrasound technique, often used in fetal, cardiac, trans-rectal and intra-vascular applications. 3D ultrasound refers specifically to the volume rendering of ultrasound data and is also referred to as 4D (3-spatial dimensions plus 1-time dimension) when it involves a series of 3D volumes collected over time. When generating a 3D volume the ultrasound data can be collected in 4 common ways. Freehand, which involves tilting the probe and capturing a series of ultrasound images and recording the transducer orientation for each slice. Mechanically, where the internal linear probe tilt is handled by a motor inside the probe. Using an endoprobe, which generates the volume by inserting a probe and then removing the transducer in a controlled manner. The fourth technology is the matrix array transducer that uses beamsteering to sample points throughout a pyramid shaped volume.
Three-dimensional and four-dimensional sonography lasts about 25 minutes if the fetus is in an optimal condition and requires more time in multiple cases.