Scanning of a volume instead of scanning single slices. The phase encoding gradient is used for two directions.

(3D FT) A specialized 3D imaging technique that uses computer processing to combine individual slice acquisitions together to produce an image that represents length, width and height.

A technique, which produces a 3 dimensional image of an object. The advantage of this approach is that the signal, acquired from the entire volume has an increased SNR. 'Slices' are defined by a second phase encoded axis, which divides the volume into 'partitions'. There is no gap between the slices in 3D volume imaging, therefore thin slices are possible. The Gz phase encoding gradient is set for several slices in one. But 3D takes more time with thin slices because of this phase encoding gradient. With conventional thin slice imaging, the SNR is poor, with 3D volume imaging this is not the case because the slab (volume) is responsible for SNR.

(3D MRA) The 3D angiography technique can be applied to focus on fast flowing (arterial) blood and to visualize small tortuous vessels. 3D TOF images are less sensitive to turbulent flow artifacts. The advantage of this approach is that the signal, acquired from the entire volume has an increased signal to noise ratio. Slices are defined by a second phase encoded axis, which divides the volume into 'partitions'. 3D TOF MRA is acquired with 3D FT slabs or multiple overlapping thin 3D FT slabs (MOTSA) depending on the coverage required and the range of flow-velocities under examination.
Such 3D techniques can provide equal spatial resolution along all three axes, i.e. be 'isotropic', or the partition thickness can be greater or less than the in plane spatial resolution in which case can be said to be 'anisotropic'. The circle of Willis, anatomy as well as its fast arterial flow, lends itself well to both 3D TOF and 2D or 3D phase contrast angiography.