FLAIR sequence - confusion

[KLPM]

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There is something I don't really understand which I hope the wiser ones can enlighten me.

If the point of inversion recovery sequence is to obtain a heavy T1 image then why does FLAIR sequence give a CSF suppressed T2?

Or am I completely misunderstanding something? 🙁

 

[cowme]

To point of FLAIR is to null a certain kind of signal from one particular entity (which is usually water on T2 weighted sequences). FLAIR can also null signals on T1 weighted images, but this is much less common

 

[Shifty B]

FLAIR sequences begin with an inversion recovery pulse of 180 degrees which is followed by a conventional (or fast) spin echo sequence at a time TI later. If you choose TI = ln (2) * T1 of CSF, then at time TI the longitudinal signal of CSF has decayed to a point where it has no longitudinal magnetization.

Then you start your spin echo sequence. If your spin echo has a relatively long TE and TR, then you get a T2 weighted image, but fluid started with no signal because of the initial inversion.

STIR is the same thing with a shorter TI, where TI = ln (2) * T1 of fat. In this way fat gets nulled.

 

[MossPoh]

Well, that cleared it up. 😛