T2*-weighted imaging

T2*-weighted imaging is a type of magnetic resonance imaging (MRI) that uses a specific MRI sequence to generate image contrast. This contrast is based on the differences in the T2* relaxation times of different tissues.

Overview

T2*-weighted imaging is a form of spin echo imaging. It is sensitive to the presence of deoxyhemoglobin, intracellular methemoglobin, and other substances that cause a local magnetic field inhomogeneity. This makes it particularly useful for detecting small hemorrhages and microbleeds, as well as for functional MRI (fMRI) studies.

Principle

The T2* relaxation time is influenced by both the T2 relaxation and the magnetic field inhomogeneity. In T2*-weighted imaging, the signal is obtained after a single radiofrequency pulse, and the image contrast is influenced by the T2* decay. This results in a high sensitivity to magnetic susceptibility differences between tissues, which can be used to detect various pathologies.

Applications

T2*-weighted imaging is widely used in clinical practice. It is particularly useful for detecting small hemorrhages and microbleeds, which appear as hypointense (dark) areas on the images. This is due to the magnetic susceptibility effect of deoxyhemoglobin, which shortens the T2* relaxation time.

In addition, T2*-weighted imaging is used in functional MRI (fMRI) studies. In these studies, the T2*-weighted images are used to detect changes in blood oxygenation level-dependent (BOLD) contrast, which reflects local changes in brain activity.

Limitations

While T2*-weighted imaging is a powerful tool, it also has some limitations. It is sensitive to magnetic field inhomogeneities, which can cause image distortion and signal loss. Furthermore, the T2* relaxation time is relatively short, which can limit the image quality.

See also

• Magnetic resonance imaging
• Spin echo
• Functional magnetic resonance imaging
• Hemorrhage
• Microbleed

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