CT Calibration Object with Embedded Markers
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Solution Overview
Problem
Existing X-ray computed tomography (CT) calibration methods require accurate prior information about the 3D relative positions of markers, which introduces errors and complicates the calibration process, limiting the accuracy and efficiency of system calibration.
Innovation Solution
A method that uses a dedicated calibration object with strongly X-ray attenuating markers in a weakly attenuating supporting material, allowing for the determination of geometrical parameters of the CT system solely from radiographic images without requiring external measurements, by fitting ellipses to the imaged trajectories of markers and using a non-linear least-squares solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If accurate prior information about 3D relative positions of markers is used for calibration, then calibration accuracy is improved, but the complexity of the calibration process increases and additional measuring devices are required
Solution Approach 1:
The calibration object serves itself by containing markers with known 3D relative positions that are directly observable in 2D projections. The calibration process uses only the radiographic system itself to determine geometrical parameters, without requiring external measuring devices like CMM arms or optical scanners. The known marker configurations in the calibration object provide self-contained reference information for calibration.
Solution Approach 2:
The invention extracts only the essential calibration information (marker positions and configurations) directly from the radiographic images themselves, rather than requiring separate external measurements. By taking out the calibration reference data and embedding it within the calibration object's known geometry, the method eliminates the need for additional measuring devices and external measurement processes.
2Measurement precision
If accurate prior information about marker positions is required, then calibration accuracy is improved, but the time and efficiency of calibration deteriorates
Solution Approach 1:
The calibration object is designed in advance with markers arranged in specific known 3D configurations. This preliminary setup of known marker positions allows the calibration process to proceed directly from radiographic images without requiring time-consuming external measurements. The known geometry is prepared beforehand and can be directly used for calibration calculations.
Solution Approach 2:
The invention replaces mechanical measurement systems (CMM arms, tactile probes) with a purely radiographic imaging-based calibration method. By substituting external mechanical measurement devices with image-based marker detection and geometric analysis, the calibration process becomes faster and more efficient while maintaining accuracy.
3Measurement precision
If external measurement devices are used for calibration, then measurement accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The radiographic system performs multiple functions: it both images the calibration object and determines geometrical parameters for calibration. The same imaging system used for actual workpiece inspection also serves the calibration function, eliminating the need for dedicated external measuring devices. This multi-functionality reduces overall system complexity and cost.
Solution Approach 2:
The calibration system uses only itself (the radiographic system) to perform calibration, without requiring external measuring devices. The known marker configurations in the calibration object provide self-contained reference information that the radiographic system can process directly to determine its own geometrical parameters.
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 enables accurate and efficient calibration of the CT system, improving the accuracy of geometrical parameter determination and reducing the need for additional measuring devices, allowing on-site calibration without relying on manufacturer-provided information, and achieving sub-pixel level precision in image coordinates.
Implementation Method 1
X-rays emitted by the source are attenuated by the sample and detected by the detector. The degree of attenuation of X-rays passing through the sample, and therefore the intensity of the X-rays detected by the detector, depends on characteristics of the sample.
Implementation Method 2
The calibration object is imaged in the CT system as outlined above. The calibration object is also measured using another metrology method, such as using an optical scanner or touch probe attached to a coordinate measuring machine arm (CMM arm).
Data Source
AI summary
A calibration object is imaged in a radiographic system such as a CT system. The images are processed to calibrate the system, without prior measurement of the calibration object. Initial estimates are refined to improve accuracy.