FLAIR MRI

FLAIR MRI

FLAIR MRI, or Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging, is a specialized MRI sequence used in neuroimaging to enhance the visibility of certain brain pathologies. This technique is particularly useful in identifying lesions in the brain that are associated with conditions such as multiple sclerosis, stroke, and other neurological disorders.

History and Development

The FLAIR sequence was developed to improve the detection of lesions in the brain by suppressing the signal from cerebrospinal fluid (CSF). This suppression allows for better contrast between lesions and the surrounding brain tissue, making it easier to identify abnormalities that may not be visible on standard T1 or T2-weighted images.

Technical Principles

FLAIR MRI is a type of inversion recovery sequence. It uses an inversion pulse to nullify the signal from fluids, particularly CSF. The sequence begins with a 180-degree inversion pulse, followed by a delay known as the inversion time (TI), which is specifically chosen to null the signal from CSF. After the inversion time, a 90-degree excitation pulse is applied, and the resulting signal is acquired. The typical inversion time for FLAIR is around 2000-2500 milliseconds, depending on the magnetic field strength and the specific parameters of the MRI machine.

Clinical Applications

FLAIR MRI is particularly useful in the following clinical scenarios:

• Multiple Sclerosis (MS): FLAIR is highly sensitive in detecting demyelinating plaques in the white matter of the brain, which are characteristic of MS.
• Stroke: It can help identify areas of ischemia or infarction, especially in the subacute and chronic phases.
• Tumors: FLAIR can help delineate the extent of brain tumors by highlighting edema and non-enhancing tumor components.
• Infections: It is useful in detecting brain infections such as abscesses or encephalitis, where it can highlight areas of inflammation.

Advantages and Limitations

Advantages

• Improved Lesion Detection: By suppressing the CSF signal, FLAIR provides better contrast for lesions adjacent to the ventricles or in the subarachnoid space.
• Non-Invasive: Like other MRI techniques, FLAIR is non-invasive and does not involve ionizing radiation.

Limitations

• Longer Scan Time: FLAIR sequences typically take longer to acquire than standard T1 or T2-weighted images.
• Sensitivity to Motion: The longer acquisition time makes FLAIR more susceptible to motion artifacts.
• Limited Use in Acute Stroke: In the hyperacute phase of stroke, diffusion-weighted imaging (DWI) is more sensitive than FLAIR.

Also see

• Magnetic Resonance Imaging
• T1-weighted MRI
• T2-weighted MRI
• Diffusion-weighted imaging
• Multiple Sclerosis