Fluid-attenuated inversion recovery

Axial fluid-attenuated inversion recovery MRI image demonstrating tumor-related infiltration involving lenticular nuclei (Arrow).

Axial fluid-attenuated inversion recovery MRI image demonstrating tumor-related infiltration involving both temporal lobes (Short arrow), and the substantia nigra (Long arrow).

Fluid-attenuated inversion recovery (FLAIR) is a pulse sequence used in magnetic resonance imaging which was invented by Dr. Graeme Bydder. FLAIR can be used with both three-dimensional imaging (3D FLAIR) or two dimensional imaging (2D FLAIR).

The pulse sequence is an inversion recovery technique that nulls 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 hyperintense lesions, such as multiple sclerosis (MS) plaques.^[1]

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:

$\textrm{TI} = \ln(2) \cdot T_1,\,$

in other words, one should typically use a TI of around 70% of the T₁ value. In the case of CSF suppression, one aims for 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.^[2]

Clinical applications

The FLAIR sequence analysis has been especially useful in the evaluation and study of CNS disorders, involving:^[2]

• Lacunar infarction
• Multiple sclerosis (MS) plaques
• Subarachnoid haemorrhage
• Head trauma
• Meningitis and other leptomeningeal diseases*

* Post-contrast FLAIR images have been added to diagnosis protocol for accurate medical assessment.^[2]

See also

• Relaxation (NMR)

References

1. Bakshi R, Ariyaratana S, Benedict RH, Jacobs L. Fluid-attenuated inversion recovery magnetic resonance imaging detects cortical and juxtacortical multiple sclerosis lesions PMID 11346369
2. "Fluid attenuation inversion recovery | Radiology Reference Article | Radiopaedia.org". radiopaedia.org. Retrieved 2015-12-03.

Further reading

• McRobbie D., et al. MRI, From picture to proton. 2003 p.40-42
• Hashemi Ray, et al. MRI, The Basics 2ED. 2004. p.272