What is the difference between 4D and 3D color Doppler ultrasound?

Two-dimensional ultrasound is plane imaging, three-dimensional ultrasound is based on two-dimensional ultrasound, from plane to three-dimensional imaging, and four-dimensional ultrasound is further based on three-dimensional ultrasound, but also increased the dimension of time, is dynamic three-dimensional imaging. All imaging basis is two-dimensional image, two-dimensional image definition is the highest, all three-dimensional, four-dimensional ultrasound imaging is based on two-dimensional image, after some re-processing and formed. Three-dimensional is stereoscopic image, four-dimensional is dynamic three-dimensional imaging, so two-dimensional ultrasound must be done throughout pregnancy, three-dimensional and four-dimensional ultrasound is done under conditions, not necessarily three-dimensional and four-dimensional ultrasound, but also on the basis of fetal malformation screening, but the basis of fetal malformation screening is two-dimensional ultrasound.