Glossary of Select Neuroimaging Terminology
BOLD (blood oxygenation level–dependent)
fMRI technique to demarcate areas of high activity in a patient’s brain while the patient performs a specific task.
CTV (computed tomography venography)
CT technique in which the venous vasculature is visualized. It is less susceptible to artifacts in comparison to MRV.
DWI (diffusion-weighted imaging) and ADC (apparent diffusion coefficient)
MRI techniques used to detect acute and subacute stroke and to differentiate vasogenic from cytotoxic edema.
FLAIR (fluid-attenuated inversion recovery)
MRI technique that highlights T2-hyperintense abnormalities adjacent to CSF-containing spaces, such as the ventricles, by suppressing CSF signal intensity.
fMRI (functional magnetic resonance imaging)
MRI technique that allows visualization of more active brain areas during a specific task, such as reading.
Paramagnetic contrast agent administered intravenously to enhance lesions.
IR (inversion recovery) and TI (interpulse time)
MRI pulse sequence that nulls the bright signal of fat or water to create a FLAIR or STIR image. During MRI, initial 180° radiofrequency pulses are followed by a 90° pulse and immediate acquisition of the signal; in IR sequences, the interpulse time is given by TI.
Unit used to measure the absorbed dose of radiation. 1 mGy = 10–3 Gy.
MRV (magnetic resonance venography)
A MRI imaging technique used to visualize the venous vasculature.
Process by which an element releases (re-emits) energy that has been absorbed from the radiofrequency pulses during an MRI sequence.
SE (spin echo)
In the most commonly employed SE sequence, a 180° pulse follows a 90° pulse. For T2-weighted images, the 90° pulse is followed by 2 180° pulses. The first 180° pulse is administered at one-half the TE (time to echo), and the second 180° pulse is administered one full TE later. The “first echo” image is referred to as proton density, and the “second echo” is T2-weighted.
STIR (short tau [or TI] inversion recovery)
MRI technique that suppresses the bright signal of fat by combining short TI inversion recovery and a fast SE sequence.
Time required for 63% of protons to return to the longitudinal plane after cessation of a 90° radiofrequency pulse. This is also referred to as the longitudinal, or spin-lattice, relaxation time.
Time required for 63% of the magnetic field in the transverse plane created by the radiofrequency pulse to dissipate. This dispersion of the magnetic vector corresponds to the exchange of spin among protons and is referred to as spin-spin relaxation; it is completed much more rapidly than is T1 relaxation.
TE (time to echo)
Time following the radiofrequency pulse in which the signal is assessed.
The unit of measure of magnetic field strength.
TR (time to repetition)
Time following the radiofrequency pulse to repetition of of the pulse.