3D spatial encoding

The particularities of 3D acquisitions are:

excitation of a complete volume at each repetition (volume = « thick slice »), rather than one thin slice
spatial encoding in 3D by adding phase encoding in the 3rd dimension in relation to the phase and frequency encodings used in 2D imaging
multiplication of the number of repetitions of a factor equal to the number of « slices» (partitions) in the third dimension to fill all the 3D k-space
reconstruction by 3D Fourier transform.

All this has consequences for:

acquisition time: given the large amount of acquired data needed to fill the 3D k-space, either very short TR sequences (echo gradient type) are used, or faster k-space filling methods.
the amount of signal: at each repetition, the signal comes from the whole volume, rather than a single slice. Therefore more signal is recorded, with fewer noise. The partitions can be finer than the classic 2D slices, because the signal to noise ratio is better compared to a slice of the same thickness acquired in 2D.
spatial resolution: the entire volume of interest is explored, with no interval between partitions, allowing fine section and multiplanar rconstructions.
artifacts: because of the two phase encodings, wraparound and truncation artifacts can be seen in two different directions.

With: