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T2*-weighted imaging of the brain 26 weeks after subarachnoid hemorrhage, showing hemosiderin deposits as hypointense areas. [1] T 2 *-weighted imaging is an MRI sequence to quantify observable or effective T 2 (T2* or "T2-star"). In this sequence, hemorrhages and hemosiderin deposits become hypointense. [2]
This image weighting is useful for assessing the cerebral cortex, identifying fatty tissue, characterizing focal liver lesions, and in general, obtaining morphological information, as well as for post-contrast imaging. To create a T2-weighted image, magnetization is allowed to decay before measuring the MR signal by changing the echo time (TE).
This image weighting is useful for assessing the cerebral cortex, identifying fatty tissue, characterizing focal liver lesions, and in general, obtaining morphological information, as well as for post-contrast imaging. To create a T 2-weighted image, magnetization is allowed to decay before measuring the MR signal by changing the echo time (TE).
Effective T2 or "T2-star" T2* Spoiled gradient recalled echo (GRE) with a long echo time and small flip angle [8] Low signal from hemosiderin deposits (pictured) and hemorrhages. [8] Susceptibility-weighted: SWI: Spoiled gradient recalled echo (GRE), fully flow compensated, long echo time, combines phase image with magnitude image [9]
At the end, images are "weighted" by the diffusion process: In those diffusion-weighted images (DWI) the signal is more attenuated the faster the diffusion and the larger the b factor is. However, those diffusion-weighted images are still also sensitive to T1 and T2 relaxivity contrast, which can sometimes be confusing.
A number of different imaging modalities or sequences can be used with imaging the nervous system: T 1-weighted (T1W) images: Cerebrospinal fluid is dark. T 1-weighted images are useful for visualizing normal anatomy. T 2-weighted (T2W) images: CSF is light, but fat (and thus white matter) is darker than with T 1.
Inversion recovery is a magnetic resonance imaging sequence that provides high contrast between tissue and lesion. It can be used to provide high T1 weighted image, high T2 weighted image, and to suppress the signals from fat, blood, or cerebrospinal fluid (CSF). [1]
These small regions of high intensity are observed on T2 weighted MRI images (typically created using 3D FLAIR) within cerebral white matter (white matter lesions, white matter hyperintensities or WMH) [1] [2] or subcortical gray matter (gray matter hyperintensities or GMH). The volume and frequency is strongly associated with increasing age. [2]