Partial volume artifact
This type of distortion, also known as a partial voluming artefact, occurs when tissues with significantly different X-ray attenuation fall into a single minimal volume element (voxel). The scanner averages these values, leading to inaccurate representation of structure boundaries and a general reduction in image clarity.
Metal artifact
Distortions from metallic objects (metallic streak artefact) are a frequent problem during scanning. They appear as bright streaks or bright areas on the image. The main culprits are:
- Metallic structures inside the skull (e.g., clips).
- Dental amalgam fillings.
These elements strongly absorb X-rays, making adjacent anatomical structures indistinguishable on the scan.
Briefly: answers to topical questions
What algorithms and methods are used to suppress metal artifacts in CT?
To suppress metal artifacts in CT, hardware, software solutions, and specialized algorithms are used.
- Hardware solutions — decreasing the helical pitch (pitch), narrowing collimation, and increasing tube current.
- Software solutions — increasing the reconstructed slice thickness or using slice-averaging methods during post-processing and multiplanar reconstruction.
- Proprietary algorithms — manufacturer-specific methods including iterative reconstruction and masking or segmentation techniques.
What CT artifacts are caused by physiological patient motion?
Physiological patient movements cause pulsation and respiration artifacts.
- Pulsation artifacts — lead to false-positive results, mainly affecting the lingular segments and the lower lobe of the left lung.
- Respiration artifacts — along with pulsation, can cause image distortions leading to false-negative diagnostic results.
What is a beam hardening artifact and how is it visualized?
The beam hardening artifact (beam hardening) is associated with strong attenuation of the X-ray beam by metallic prosthetic components or dental restorations. On CT, it can manifest as streaks and dark zones, impairing the visualization of adjacent tissues and leading to false-negative results.
Class and exam questions
Why does the partial volume artifact occur?
It occurs because structures of high and low density end up inside a single voxel, and the scanner produces an averaged density value for this area.
Which objects most commonly cause metal artifacts on head CT scans?
Usually dental amalgam and various intracranial metallic implants or surgical hardware.
What else to study on this topic
- Contrast agents: risks and precautions
- Basic principles of magnetic resonance imaging (MRI)
- Differences in signal generation in CT and MRI
- Contraindications to the use of contrast
- Safety during MRI procedures
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