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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]
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]
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.
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).
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).
T1 weighted: T1: Measuring spin–lattice relaxation by using a short repetition time (TR) and echo time (TE). Lower signal for more water content, [1] as in edema, tumor, infarction, inflammation, infection, hyperacute or chronic hemorrhage. [2] High signal for fat [1] [2] High signal for paramagnetic substances, such as MRI contrast agents [2]
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.
In MRI, T 2-weighted images can be obtained by selecting an echo time on the order of the various tissues' T 2 s. [8] In order to reduce the amount of T 1 information and therefore contamination in the image, excited spins are allowed to return to near-equilibrium on a T 1 scale before being excited again. (In MRI parlance, this waiting time is ...