Motion, which is uniform in all directions. This is generally used in reference to molecular diffusion or rotation, which gives rise to relaxation of the spin system through the dipole dipole interaction.
(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 secondphase encoded axis, which divides the volume into 'partitions'.
3D TOFMRA 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.