T2-weighted

T2-weighted Imaging

T2-weighted imaging is a fundamental technique in magnetic resonance imaging (MRI) that provides detailed information about the water content and tissue characteristics of the body. It is particularly useful in identifying pathological changes in tissues, such as edema, inflammation, and certain types of tumors.

Principles of T2-weighted Imaging

T2-weighted imaging is based on the T2 relaxation time, which is the time it takes for the transverse magnetization to decay to 37% of its original value after a radiofrequency pulse is applied. This decay is due to interactions between the magnetic fields of neighboring hydrogen nuclei, which cause the spins to dephase.

In T2-weighted images, tissues with high water content, such as cerebrospinal fluid (CSF), appear bright, while tissues with low water content, such as fat, appear darker. This contrast is achieved by using specific pulse sequences that emphasize T2 relaxation effects, such as spin echo sequences with long echo times (TE) and repetition times (TR).

Clinical Applications

T2-weighted imaging is widely used in clinical practice for:

• Neurology: Identifying lesions in the brain, such as multiple sclerosis plaques, tumors, and areas of infarction.
• Orthopedics: Evaluating joint abnormalities, such as meniscal tears and cartilage degeneration.
• Oncology: Detecting and characterizing tumors in various organs, including the liver, prostate, and breast.
• Cardiology: Assessing myocardial edema and fibrosis in conditions like myocarditis and cardiomyopathy.

Advantages and Limitations

Advantages

• High Contrast: T2-weighted images provide excellent contrast between different types of soft tissues, making it easier to distinguish between normal and pathological tissues.
• Non-invasive: MRI, including T2-weighted imaging, is a non-invasive technique that does not involve ionizing radiation.

Limitations

• Longer Scan Times: T2-weighted imaging typically requires longer scan times compared to T1-weighted imaging, which can be a limitation in patients who have difficulty remaining still.
• Susceptibility to Motion Artifacts: Movement during the scan can lead to artifacts that degrade image quality.

Technical Considerations

Pulse Sequences

Common pulse sequences used for T2-weighted imaging include:

• Spin Echo (SE): The classic sequence for T2-weighted imaging, using a 90-degree pulse followed by one or more 180-degree refocusing pulses.
• Fast Spin Echo (FSE): A variation of the spin echo sequence that acquires multiple echoes per TR, reducing scan time.

Parameters

Key parameters that affect T2-weighted imaging include:

• Echo Time (TE): Longer TE values increase T2-weighting by allowing more time for T2 decay.
• Repetition Time (TR): Longer TR values help to minimize T1-weighting, enhancing T2 contrast.

Also see

• T1-weighted imaging
• Magnetic resonance imaging
• Spin echo
• Relaxation time