# From gradient echo to echo planar

One excitation, then several echoes. These three lessons measure the echo
spacing of a train of readouts, the effect of a phase-encode blip between the
echoes, and the artefacts that remain when the whole matrix is acquired after
a single pulse.

| Page | What it establishes |
| --- | --- |
| {doc}`/generated/gallery/03-gre-to-epi/01_multi_echo` | A train of readouts of alternating polarity, and the echo spacing set by the receiver bandwidth and the gradient ramps. |
| {doc}`/generated/gallery/03-gre-to-epi/02_segmented` | A phase-encode blip between the echoes, and the exchange of scan time for geometric fidelity the shot count makes. |
| {doc}`/generated/gallery/03-gre-to-epi/03_epi` | One excitation for the whole matrix: the blurring the decay across the train produces, and the ghost a gradient delay produces. |

```{toctree}
:hidden:

/generated/gallery/03-gre-to-epi/01_multi_echo
/generated/gallery/03-gre-to-epi/02_segmented
/generated/gallery/03-gre-to-epi/03_epi
```