So how is 4D ultrasound different than 3D ultrasound? A very common question. The easiest way to describe 4D is" video" or "movement". 3D is just a still shot, but 4D is 3D "live" or 4th demension (movement), 3D in movement. It is the color images you see (3D ), but in movement (4D). Because it is "live" or in "movement," this video is often recorded onto a DVD disk in order to be able to see the video in the future.