Fluid attenuated inversion recovery

Fluid Attenuated Inversion Recovery

Fluid Attenuated Inversion Recovery (FLAIR) is a specialized magnetic resonance imaging (MRI) sequence used in the field of radiology to enhance the visibility of certain types of brain lesions. This technique is particularly useful in the detection of multiple sclerosis plaques, brain tumors, and other pathologies where the suppression of cerebrospinal fluid (CSF) is advantageous.

Principle of FLAIR

FLAIR is an inversion recovery sequence that is designed to nullify the signal from fluids, particularly CSF, in the brain. This is achieved by using a specific inversion time (TI) that suppresses the signal from fluids, allowing for better visualization of lesions that are otherwise obscured by the bright signal of CSF on conventional T2-weighted images.

The sequence begins with a 180-degree inversion pulse, followed by a delay (the inversion time) before the application of the 90-degree excitation pulse. The inversion time is carefully chosen so that the longitudinal magnetization of CSF passes through zero, effectively nullifying its signal. This results in images where the CSF appears dark, providing a stark contrast against lesions that appear hyperintense.

Clinical Applications

FLAIR is particularly useful in the following clinical scenarios:

• Multiple Sclerosis: FLAIR is highly sensitive in detecting demyelinating plaques in the white matter of the brain, which are characteristic of multiple sclerosis. These plaques appear hyperintense on FLAIR images, making them more conspicuous than on standard T2-weighted images.

• Subarachnoid Hemorrhage: In cases of subarachnoid hemorrhage, FLAIR can help identify blood in the subarachnoid space, which appears hyperintense against the suppressed CSF background.

• Brain Tumors: FLAIR can aid in the delineation of brain tumors and associated edema, as the suppression of CSF enhances the contrast between the tumor and surrounding tissues.

• Infections and Inflammatory Conditions: Conditions such as encephalitis and meningitis can be better visualized with FLAIR, as the inflammatory changes often result in hyperintense signals on FLAIR images.

Advantages and Limitations

Advantages

• Improved Lesion Detection: By suppressing the CSF signal, FLAIR enhances the visibility of lesions adjacent to the ventricles and cortical sulci.
• Increased Contrast: The sequence provides increased contrast between pathological tissues and normal brain structures.

Limitations

• Longer Scan Times: FLAIR sequences typically require longer acquisition times compared to standard T2-weighted sequences.
• Sensitivity to Motion: The longer scan times make FLAIR more susceptible to motion artifacts, which can degrade image quality.

Also see

• Magnetic Resonance Imaging
• T1-weighted imaging
• T2-weighted imaging
• Inversion recovery
• Neuroradiology