X-ray CT Edge Artifact Correction via Phantom Calibration
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Solution Overview
Problem
Existing X-ray CT apparatuses using photon counting detectors face challenges in suppressing artifacts near the edge of a test subject due to the influence of half shadows and scattered rays, which are not adequately addressed by current calibration methods.
Innovation Solution
An X-ray CT apparatus and correction method that create and utilize correction data based on difference data between measurement and calculation projection data for each X-ray energy, obtained by photographing a known phantom with a known composition and shape smaller than the imaging field, to correct projection data and reduce artifacts near the edge of a test subject.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stepped phantoms with acrylic and aluminum plates are used for calibration, then calibration data for multiple materials can be obtained, but artifacts generated in the vicinity of the edge portion of the test subject cannot be suppressed
Solution Approach 1:
The phantom is segmented into multiple regions: a central region with stepped plates for material calibration and peripheral regions with edge portions for artifact correction. This segmentation allows separate optimization of calibration accuracy and artifact suppression by using different phantom regions for different purposes.
Solution Approach 2:
The edge portion of the phantom acts as an intermediary element that captures half-shadow and scattered ray effects. By measuring these effects on the known edge portion and subtracting them from the test subject images, the harmful artifacts are eliminated while preserving the diagnostic information.
2Measurement precision
If the phantom size covers all detection elements, then complete detector calibration is achieved, but the influences of half shadows and scattered rays at the edge portion cannot be grasped
Solution Approach 1:
The phantom design extends into the spatial dimension by creating a size mismatch between the phantom and the detector array. The phantom is deliberately made smaller than the full detector coverage, creating peripheral detection elements that only receive X-rays from the phantom's edge portions, thereby capturing half-shadow and scattered ray information that would be lost with full-coverage phantoms.
3Object-affected harmful factors
If correction data is created using difference data between measurement and calculation projection data, then artifacts can be suppressed, but additional processing steps are required
Solution Approach 1:
Correction data is pre-calculated and stored during the phantom calibration phase. The correction data, which contains the characteristic half-shadow and scattered ray patterns of the phantom's edge portions, is computed in advance and saved for later use. During actual patient imaging, this pre-computed correction data is simply subtracted from the projection data, significantly reducing the computational burden and complexity of real-time artifact correction.
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
Effectively suppresses artifacts near the edge of a test subject, improving the accuracy of medical images by accounting for half shadows and scattered rays through the use of correction data.
Implementation Method 1
a photon counting type detector can measure X-ray energies that are the energies of incident X-ray photons
Implementation Method 2
measurement projection data for each X-ray energy obtained by photographing a known phantom having a known composition
Data Source
AI summary
An X-ray CT apparatus and a correction method of projection data that are capable of suppressing artifacts generated in the vicinity of an edge portion of a test subject are provided. The X-ray CT apparatus for photographing a test subject is characterized by comprising: a correction data creation unit that creates correction data using difference data between measurement projection data for each X-ray energy obtained by photographing a known phantom having a known composition, a known shape, and a size smaller than a photographing field of view of the X-ray CT apparatus and calculation projection data for each X-ray energy calculated on the basis of X-ray transmission lengths obtained from the shape of the known phantom; and a correction unit that corrects projection data for each X-ray energy of the test subject using the correction data.