Fluid attenuated inversion recovery

Last revised by Raymond Chieng on 2 Jun 2023

Fluid attenuated inversion recovery (FLAIR) is a special inversion recovery sequence with a long inversion time. This removes signal from the cerebrospinal fluid in the resulting images 1. Brain tissue on FLAIR images appears similar to T2 weighted images with grey matter brighter than white matter but CSF is dark instead of bright.


To null the signal from fluid, the inversion time (TI) of the FLAIR pulse sequence is adjusted such that at equilibrium there is no net transverse magnetization of fluid.

Clinical use

The FLAIR sequence is part of almost all protocols for imaging the brain, particularly useful in the detection of subtle changes at the periphery of the hemispheres and in the periventricular region close to CSF.

FLAIR is able to show lower concentration gadolinium compared to T1-weighted post Gadolinium imaging. In three-dimensional (3D) FLAIR imaging, foci of leptomeningeal enhancement can be seen in multiple sclerosis. Such enhancement is due to fluid leakage secondary to inflammation of the blood vessels 6.

The usefulness of FLAIR sequences has been evaluated in many diseases of the central nervous system such as 2-4:

Post-contrast FLAIR images have been included in protocols to assess leptomeningeal diseases, such as meningitis 5

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