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Understanding and correcting image artefacts in X-ray CT scans

by Morgane on 09 Aug 2021 at 13h27

X-ray Computed Tomography has become the most advanced and complete technology for non-destructive testing of parts in various areas. While it is a very innovative technology, there can be some issues to image quality in what we call artefacts. Understanding artefacts is important as you need to differentiate them from real parts features, thus correcting artefacts is possible as there are multiple options in order to minimize them.

An introduction to X-ray CT artefacts

 
Any difference between the reconstructed image obtained with an X-ray CT scan with the real sample, based on its material density and structure, is referred to as a CT image artefact.
 
On top of that, when conditions are not met when scanning a sample, artefacts will appear. Image artefacts have a regular pattern and show as bright and/or dark lines or shadows in scans.
 
 
As seen in these pictures, artefacts before and after correction:

Two principal causes for image artefacts 

 
There are various reasons to X-ray CT image artefacts, but we can distinguish two principal categories: 
 
- artefacts caused because of the CT scan set-up (sample movement for example)
- artefacts dependent on the part’s characteristics (density and structure with beam hardening, under-penetration of the X-ray source…)
 
Moreover, there can be other factors causing image artefacts such as noise and sample reconstructed poorly out of field. These are mostly due to the system’s capacities and that’s why, by the way, how crucial it is to evaluate each specific parameter when buying an X-ray CT system as detailed here.

Minimizing image artefacts in X-ray CT 

 
Identifying artefacts type and causes is an important first step to correcting them. In our complete and advanced X-ray CT software, X-Act, each cause has its programmed parameters for correction, such as the following:

Metal artefacts correction

 

Mostly caused by motion, noise, scatter… As a correction, it is an algorithm implemented in X-Act reconstruction software. Its goal is to improve reconstructed images quality when the sample scanned is composed of both dense and light materials. This tool can be very powerful when scanning plastic parts with metallic inserts inside.

  

Beam hardening

 

It is known for producing dark traces. Its correction in X-ray, allows you to remove beam artefacts from your component without having a proper spectrum estimation. It is a use guided algorithm offering a simple way to compute the estimated absorption photons curve and correct the image deviation.

  

Ring artefacts 

 

This artefact is a result from a non-linear response of the detector which generates circular artefacts centered on the rotation axis. This correction work directly on the projections and preserves the image features/resolution.

X-Act – an advanced & complete solution to correct artefacts 

 
X-Act is a powerful software with an easy and intuitive user interface. Delivered with an incredible number of functionalities, X-Act enables you to set the perfect parameters for the scanning process, for any kind of sample. For X-ray CT artefacts correction, as presented above, it includes multiple artefacts compensations plugins that enhance CT scans: geometry, focal spot movement, phase contrast, ring artefact, beam hardening, metal artefacts and many more… 
 
Discover X-Act here
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