T1 FLAIR

[Barrymagnetic]

What benefit is there in acquiring Ax T1 FLAIR sequence in brain imaging? How does T1 weighting relate to FLAIR?

[aelster]

Dear Barrymagnetic,

Your question is in two parts:

1. A T1-FLAIR sequence is an alternative to a conventional short TR/short TE spin echo (SE) sequence for T1-weighted brain imaging. Because of the inversion pulse, tissues with different T1 values can be separated over twice the dynamic range. Hence it is often noted that the distinction between gray matter and white matter on T1-FLAIR is often superior to that on T1-weighted spin echo. In practice, T1-FLAIR may provide superior delineation of contrast-enhancement. See the example in this related Q&A:

http://mriquestions.com/best-t1-pulse-sequence.html

The benefit of T1-FLAIR is especially dramatic at 3.0T and above, where field-related prolongation of tissue T1 values makes short TR/short TE SE imaging impractical. At 1.5 T which one to use is a toss-up. The T1-FLAIR takes a little longer but looks nicer.

2. T1-weighting and FLAIR are interconnected but somewhat separate concepts. FLAIR simply means that fluid signal is being suppressed through an inversion recovery mechanism. This can be made to happen either with T1-weighting (T1-FLAIR) or T2-weighting (T2-FLAIR) of other tissues.

I hope this helps. Thank you for your question.

[Barrymagnetic]

Thank you aelster!

[AndrewBworth]

Another advantage of T1-FLAIR is that it can be used with methods that lead to a variable TR. For example, when the initiation of the pulse sequence is dependent on a patient's respiration - regular T1 sequences cannot be used because the contrast is dependent on the TR. However in T1-FLAIR, we are dependent on TR simply exceeding some minimum value. In these protocols - it is probably ideal if the time between pulse sequence initiation and echo acquisition is as short as possible - so T1 weighted GRE sequences may be preferred, but T1 FLAIRS are a possibility. Also, T1-FLAIR methods appear to be more compatible with BLADE/PROPELLER sequences because they can achieve a higher turbo factor than regular T1 sequences (why this is, the lightbulb has not yet turned on). The turbo factor on T1-FLAIR BLADE at my current hospital is 19, whereas the turbo factor on T1 sequences is usually 3. I believe for BLADE to be used with its motion correction post processing algorithm - the turbo factor/blade width must be higher, (I have read 29, but I don't know my systems specifics) - this could be accomplished with a GRAPPA dependent scheme.