Fluidattenuated

Fluidattenuated refers to imaging techniques that reduce or suppress signals from bodily fluids to improve contrast between tissues. In magnetic resonance imaging, the most widely used example is the fluid-attenuated inversion recovery (FLAIR) sequence, which suppresses cerebrospinal fluid (CSF) signal to reveal pathology adjacent to CSF spaces.

Principle: FLAIR uses an inversion recovery preparation with an inversion time selected to null the signal from CSF, followed by a T2-weighted readout. This makes normally dark CSF spaces appear dark while many pathologies remain hyperintense, improving visibility of lesions near ventricles and along the cortical sulci. The exact TI and image quality depend on field strength (commonly 1.5 Tesla or 3 Tesla) and the specific protocol.

Applications: FLAIR is widely used in neuroimaging to detect demyelinating lesions such as multiple sclerosis plaques, edema, gliosis, infections, tumors, and subarachnoid or meningeal processes that are otherwise difficult to discern when CSF is bright on standard T2-weighted images. It is often included in routine brain MRI protocols for comprehensive assessment.

Limitations: The sequence can be longer to acquire and is sensitive to magnetic field inhomogeneities and patient motion. CSF nulling can sometimes obscure fine CSF details and may affect interpretation near certain anatomical regions. It is one tool among many in MRI and is not intended to replace other sequences for acute hemorrhage or vascular imaging.

Other uses: In addition to CSF suppression, the general concept of fluid attenuation appears in other MRI contrasts and in other modalities that seek to reduce fluid signal to improve tissue differentiation.