Question

Enumerate the various MRI artefacts and discuss any four of them in brief.

Hint:

To minimize MRI artefacts, ensure patient immobility, avoid metallic objects near the scanning area, and adjust scan parameters to reduce ghosting and aliasing effects.

Answer 1

Step 1: Enumerating MRI artefacts.
MRI artefacts are distortions or errors in MRI images that are not related to the actual anatomy of the body. These artefacts can arise due to various reasons, including patient movement, equipment malfunction, or the intrinsic properties of the MRI scan. Common MRI artefacts include:
1. Motion artefacts
2. Ghosting artefacts
3. Metal artefacts
4. Chemical shift artefacts
5. Aliasing artefacts
6. Zipper artefacts
7. Truncation artefacts
8. Susceptibility artefacts

Step 2: Discussing four common MRI artefacts.
1. Motion Artefacts:
Motion artefacts are caused by patient movement during the MRI scan. These artefacts appear as blurring or doubling of the image. It is most common in brain, neck, and abdominal imaging. The artefact arises because MRI images are built up from a series of slices, and if the patient moves during scanning, the relative positions of the slices are altered.

2. Ghosting Artefacts:
Ghosting occurs when there is a mismatch between the time when the data is collected and the data being measured. This artefact typically results in a mirror image, often seen in phase encoding direction. It is caused by either patient movement or magnetic field inhomogeneity.

3. Metal Artefacts:
Metal artefacts arise when metallic objects (e.g., implants, dental work) distort the magnetic field, leading to signal loss or distortion in the images. These artefacts appear as dark or bright streaks around the metal, especially in high-field strength MRIs.

4. Chemical Shift Artefacts:
Chemical shift artefacts are caused by the difference in resonance frequencies of protons in different chemical environments. For example, fat and water have different frequencies, and when imaging, this difference can cause misplacement of fat and water signals, leading to artefacts at the interface between fat and water-containing tissues.

Step 3: Conclusion.
MRI artefacts are common in clinical practice and can often interfere with the diagnostic quality of the images. Understanding these artefacts and their causes is important for improving image quality and reducing distortion during scans.