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Fluid-attenuated inversion recovery (FLAIR) is a magnetic resonance imaging sequence with an inversion recovery set to null 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 ]
Fluid-attenuated inversion recovery (FLAIR) [2] is an inversion-recovery pulse sequence used to nullify the signal from fluids. For example, it can be used in brain imaging to suppress cerebrospinal fluid so as to bring out periventricular hyperintense lesions, such as multiple sclerosis plaques.
Axial T2 FLAIR sequence MR image of a middle-aged man with leukoaraiosis. MRI image: Leukoaraiosis in a 90-year-old patient with cerebral atrophy. Head CT showing periventricular white matter lesions. Leukoaraiosis is a particular abnormal change in appearance of white matter near the lateral ventricles. It is often seen in aged individuals ...
The key to Phase-contrast MRI (PC-MRI) is the use of a bipolar gradient. [4] A bipolar gradient has equal positive and negative magnitudes that are applied for the same time duration. The bipolar gradient in PC-MRI is put in a sequence after RF excitation but before data collection during the echo time of the generic MRI modality.
MRI scans showing hyperintensities. A hyperintensity or T2 hyperintensity is an area of high intensity on types of magnetic resonance imaging (MRI) scans of the brain of a human or of another mammal that reflect lesions produced largely by demyelination and axonal loss.
The MRI of patients with VWM shows a well defined leukodystrophy. These MRIs display reversal of signal intensity of the white matter in the brain. Recovery sequences and holes in the white matter are also visible. [4] Over time, the MRI is excellent at showing rarefaction and cystic degeneration of the white matter as it is replaced by fluid.
The degeneration of white matter, which reflects the degeneration of myelin, can be seen in a basic MRI and used to diagnose leukodystrophies of all types. T-1 and T-2 weighted fluid-attenuated inversion recovery (FLAIR) images are the most often used approach. [25] Electrophysiological and other kinds of laboratory testing can also be done.
To sensitize MRI images to diffusion, the magnetic field strength (B1) is varied linearly by a pulsed field gradient. Since precession is proportional to the magnet strength, the protons begin to precess at different rates, resulting in dispersion of the phase and signal loss.