Fluid attenuated inversion recovery

Fluid-attenuated inversion recovery (FLAIR) is a MRI sequence, magnetic resonance imaging sequence with an inversion recovery set to null fluids. For example, it can be used in brain imaging to suppress cerebrospinal fluid (CSF) effects on the image, so as to bring out the periventricular Hyperintensity, hyperintense lesions, such as multiple sclerosis (MS) plaques. It was invented by Graeme Bydder, Joseph Hajnal, and Ian Young in the early 1990s. FLAIR can be used with both three-dimensional imaging (3D FLAIR) or two dimensional imaging (2D FLAIR).

Technique

By carefully choosing the inversion time (TI), the signal from any particular tissue can be nulled. The appropriate TI depends on the tissue via the formula:

:$\textrm = \ln(2) \cdot T_1,\,$

in other words, one should typically use a TI of around 70% of the Spin-lattice relaxation time, ''T₁'' value. In the case of CSF suppression, one aims for Spin-lattice relaxation time, ''T₁''-weighted images, which prioritize the signal of fat over that of water. Therefore, if the long TI (inversion time) is adjusted to a zero crossing point for water (none of its signal is visible), the signal of the CSF is theoretically being "erased," from the derived image.

Clinical applications

The FLAIR sequence analysis has been especially useful in the evaluation and study of Central nervous system disease, CNS disorders, involving:
* Lacunar stroke, Lacunar infarction
* Multiple sclerosis, Multiple sclerosis (MS) plaques
* Subarachnoid hemorrhage, Subarachnoid haemorrhage
* Head injury, Head trauma
* Meningitis and other Leptomeningeal, leptomeningeal diseases*
* Post-contrast FLAIR images have been added to diagnosis protocol for accurate medical assessment.

File:Gliomatosis cerebri2.jpg, Axial fluid-attenuated inversion recovery MRI image demonstrating tumor-related infiltration involving lenticular nuclei (Arrow).
File:Gliomatosis cerebri.jpg, Axial fluid-attenuated inversion recovery MRI image demonstrating tumor-related infiltration involving both temporal lobes (Short arrow), and the substantia nigra (Long arrow).

See also

*Relaxation (NMR)

References

Further reading

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Magnetic resonance imaging

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