Gradient echo sequence use in MRI BRAIN

Gradient echo sequence to show susceptibility differences

In gradient echo sequence, we usually use a short TE such as 2ms. If we use a very long TE like 40ms to eliminate T2 effects, the magnetic field inhomogeneity can act as contrast in the image. As blood iron concentration can affect the local magnetic field, a gradient echo sequence with a long TE is able to indicate micro-hemorrhage in the brain. 
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Signals from substances with different magnetic susceptibilities compared to their neighboring tissue will become out of phase with these tissues at sufficiently long TEs. There’s good contrast between gray matter and white matter, iron-laden tissues, venous blood vessels, and other tissues with susceptibilities that are different from the background tissue.