X-ray CT Metal Artifact Reduction via High Frequency Component Extraction
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Solution Overview
Problem
Existing X-ray CT image reconstruction methods suffer from image quality deterioration due to metal artifacts, which are not effectively addressed without losing structure information, especially when imaging subjects containing metal.
Innovation Solution
The method involves extracting high frequency components from error projection data, weighting them to suppress metal artifacts, and restoring them to primary corrected projection data for image reconstruction, using CT values corresponding to soft tissue subtracted from metal regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If metal artifact reduction is performed by substituting metal portions in projection data, then metal artifacts are reduced, but structure information (bone, soft tissue) coinciding with metal portions is lost and image quality deteriorates
Solution Approach 1:
The projection data is segmented into three distinct components: metal projection data (extracted from initial image data), composition classification projection data (from classified tissue types), and structure projection data (high-frequency details). This segmentation allows selective processing where metal portions are corrected without losing underlying structure information, as each component can be reconstructed and combined independently to preserve both artifact reduction and structural integrity
Solution Approach 2:
Structure projection data acts as an intermediary that bridges the gap between metal-corrected regions and original structure information. By extracting high-frequency components from the difference between initial and corrected projection data, the patent introduces this intermediary element that carries structure information through the correction process, allowing it to be preserved in the final reconstructed image even in regions where metal artifacts originally obscured them
2Object-affected harmful factors
If all tissues coinciding with metal portion are substituted, then metal artifact is reduced, but information on structure (bone, soft tissue) is lost
Solution Approach 1:
The patent applies local quality by treating different regions of the projection data differently. Structure projection data preserves high-frequency information locally in regions where metal artifacts would otherwise obscure structure details. The composition classification maintains accurate tissue typing in non-metal regions, while structure projection data injects preserved structural details into metal-affected regions, ensuring measurement precision is maintained locally throughout the image
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces metal artifacts while maintaining image quality and preserving structure information, preventing image quality deterioration during X-ray CT imaging of subjects with metal.
Implementation Method 1
An X-ray CT apparatus is such that a subject is penetrated, an X-ray attenuated in accordance with an X-ray attenuation coefficient of a substance (composition) inside the penetrated subject is received in an X-ray detector
Implementation Method 2
The X-ray used is a polychromatic X-ray, and beam hardening correction in accordance with the substance is carried out
Data Source
AI summary
In order to reduce a metal artifact using a short process, without causing image quality deterioration, when a subject containing metal is imaged in an X-ray CT apparatus, the invention is such that a high frequency component is extracted utilizing the fact that a high frequency component is a structure in error projection data, which are a difference between primary corrected projection data wherein at least one portion of an artifact component caused by metal has been removed and photographed projection data acquired by imaging. The high frequency component, extracted while carrying out weighting in order to suppress the metal artifact, is restored to the primary corrected projection data, after which an image is reconstructed. Also, metal projection data used when compiling the primary corrected projection data are calculated from a value that is a CT value corresponding to soft tissue subtracted from a CT value of a metal region.