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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]
A hyperintensity or T2 hyperintensity is an area of high intensity on types of ... on an MRI image and the term "bright signal" is occasionally used as a synonym for ...
The presence of high or moderate signal intensity on both T1 and T2 images is related to the ratio of fat to vessels and edema. For example, a VH with a high concentration of fat and a relatively low make-up of vessels and edema would show a high signal intensity on T1-weighted spin-echo images and intermediate signal intensity on T2-weighted ...
A conventional gradient echo T2*-weighted image (left, TE=20 ms) shows some low-signal foci associated with CAA. On the other hand, an SWI image (center, with a resolution of 0.5 mm x 0.5 mm x 2.0 mm, projected over 8mm) shows many more associated low-signal foci. Phase images were used to enhance the effect of the local hemosiderin build-up.
In this case the loss of coherence is described as a "static dephasing". T2* is a measure of the loss of coherence in an ensemble of spins that includes all interactions (including static dephasing). T2 is a measure of the loss of coherence that excludes static dephasing, using an RF pulse to reverse the slowest types of dipolar interaction.
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.
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T2 weighted: T2: Measuring spin–spin relaxation by using long TR and TE times Higher signal for more water content [1] Low signal for fat in standard Spine Echo (SE), [1] though not with Fast Spin Echo/Turbo Spin Echo (FSE/TSE). FSE/TSE is the standard of care in modern medicine because it is faster.