Why do we not measure FID but the gradient recalled echo?

[Joe]

not expert, however I googled and found this is maybe related to k-space:

If the 90-FID imaging sequence presented in the previous chapter was used, we would record only half of k-space. We would like to produce the equivalent of an echo in the center of our acquisition window when the frequency encoding gradient is turned on. This would give us both the left and right halves of k-space.


https://www.sciencedirect.com/topics/neu...tion-decay
https://www.cis.rit.edu/htbooks/mri/chap-8/chap-8.htm