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### 0 FLAIR

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.
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 T2 weighted images.