The FLAIR (Fluid Attenuated Inversion Recovery) sequence is a specialized MRI sequence that is very similar to the T2 sequence, except that the signal from cerebrospinal fluid is nulled and therefore appears black.
Applications
The FLAIR sequence is well suited for demonstrating abnormalities in the cerebrospinal fluid. Multiple sclerosis plaques, lesions of the white matter, tumors, edema, encephalomalacia, gliosis, and acute infarctions appear as hyperintense signals on the FLAIR sequence.
Brain tumors
The FLAIR sequence is highly sensitive to subtle differences in soft-tissue contrast and can depict the full extent of the tumor and the associated tumor-related changes far better than contrast-enhanced T1-weighted imaging. Furthermore, FLAIR imaging has been shown to be superior to contrast-enhanced T1-weighted imaging both in detecting subtle leptomeningeal tumor spread and in depicting lesions with a low contrast ratio[^2].
Subarachnoid hemorrhage
The FLAIR sequence is also ideally suited for detecting acute Subarachnoid hemorrhage on MRI[^1].
