Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique that provides detailed views of the body’s internal structures. It uses strong magnetic fields and radio waves to image internal structures like organs, soft tissues, and bone. Unlike X-rays or CT scans, MRI does not employ ionizing radiation. Radiologists can adjust MRI settings, called sequences, to highlight specific tissues or abnormalities.
How FLAIR MRI Works
FLAIR stands for Fluid-Attenuated Inversion Recovery, a specialized MRI sequence. It suppresses the signal from cerebrospinal fluid (CSF), which normally appears bright white on other common MRI sequences like T2-weighted images. This is similar to turning down glare from water to see objects beneath.
In standard T2-weighted scans, both CSF and certain brain lesions can appear bright, making them difficult to distinguish. The FLAIR sequence applies a specific pulse and timing to make the CSF appear dark. This suppression allows lesions, which retain their bright signal, to stand out more clearly against the dark CSF background. This is useful for identifying abnormalities near fluid-filled spaces, such as the brain’s ventricles or the cerebral cortex surface.
Clinical Applications of FLAIR Imaging
FLAIR imaging is a valuable tool in neuroradiology, offering advantages for diagnosing and monitoring neurological conditions. Its ability to suppress CSF signal highlights subtle abnormalities.
FLAIR sequences are the preferred method for detecting Multiple Sclerosis (MS) lesions. These demyelinating plaques frequently form in the periventricular white matter. By making the CSF dark, FLAIR allows these bright MS lesions to become clearly visible and quantifiable, aiding in diagnosis and disease progression assessment.
This technique also detects strokes, particularly in their subacute phase, typically 6 hours to 4 days after onset. FLAIR highlights subtle ischemic changes in brain tissue, where blood flow has been restricted. These changes appear as bright signals, helping clinicians identify the extent and location of brain injury.
FLAIR is beneficial in cases of meningitis and encephalitis, which involve inflammation of the meninges (the membranes surrounding the brain and spinal cord) and the brain tissue. The sequence can reveal increased signal intensity in inflamed meninges or within the brain, indicating active inflammatory processes. This assists in diagnosing these infections and monitoring treatment response.
The sequence is useful for detecting other subtle brain abnormalities difficult to see on conventional MRI scans. Examples include low-grade tumors that blend with surrounding tissue or subtle changes from head trauma. FLAIR’s enhanced contrast improves the visibility of these pathologies, contributing to earlier and more accurate diagnoses.
The Patient Experience
From a patient’s perspective, undergoing a FLAIR MRI scan is generally similar to having a standard brain MRI. Patients lie still on a cushioned table that slides into the cylindrical opening of the MRI scanner. Maintaining stillness is important throughout the procedure to ensure clear images are obtained.
During the scan, patients will hear various loud knocking, buzzing, and whirring sounds as the magnetic fields are rapidly switched on and off. To mitigate this noise, the technologist typically provides headphones or earplugs. Communication with the technologist is maintained through an intercom system, allowing the patient to speak if necessary.
A brain MRI, including FLAIR sequences, typically lasts between 30 to 60 minutes, depending on the specific protocols and the number of sequences required. In some cases, a contrast agent, such as gadolinium, may be administered intravenously. This agent is a separate consideration from the FLAIR sequence itself and is used to highlight different features, such as areas of active inflammation or disruption of the blood-brain barrier.