 The name is derived from the addition of time (as the fourth dimension) to traditional 3D computed tomography.Alternatively, the phase of a particular process, such as respiration, may be considered the fourth dimension.Fluoroscopy is a similar technique to 4DCT, however it refers to the introduction of a time element to 2D planar radiography, rather than to 3D CT.

4DCT is used in radiation therapy planning to reduce doses to healthy organs such as the heart or lungs.