Computed Tomography Nonlinearity Correction via Optimization
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Solution Overview
Problem
Existing methods for correcting nonlinearities in computed tomography image data, particularly due to beam hardening and stray radiation, are influenced by user-selected threshold values, leading to systematic errors in dimensional metrology.
Innovation Solution
A method that determines a set of correction functions based on user-selectable ascertainment parameters, minimizing differences between corrected radiographs or reconstructed volumes, thereby reducing user influence and achieving optimized correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a correction polynomial with empirically determined coefficients is used to linearize attenuation values, then beam hardening and stray radiation nonlinearities are corrected, but the coefficients depend strongly on the test object and require re-determination for each component class, leading to user influence through threshold value selection and systematic errors in dimensional metrology
Solution Approach 1:
The patent transforms the correction approach by changing from object-specific parameter determination to universal parameter determination. Instead of determining correction polynomial coefficients separately for each test object class, the system determines a single set of correction parameters that works universally across different component classes. This is achieved by formulating the correction function determination as an optimization problem that minimizes a cost function representing the deviation from linearity across multiple test objects simultaneously, thereby eliminating the need for re-determination for each component class and reducing user influence.
2Reliability
If correction functions are determined individually for each test object class, then accurate correction is achieved for that specific class, but the method requires substantial user input and threshold value selection, introducing systematic errors
Solution Approach 1:
The patent implements self-service by enabling the correction system to automatically adapt to different test objects without requiring user intervention for parameter selection. The system performs self-calibration by processing test objects and automatically determining optimal correction parameters through optimization algorithms. The cost function minimization process automatically identifies the best correction parameters based on the actual test data, eliminating the need for users to manually select threshold values or determine component-specific correction functions, thereby reducing user influence and systematic errors.
3Ease of manufacture
If a single correction function is used for all test objects, then the determination process is simplified, but accurate correction cannot be achieved for diverse component classes with different attenuation characteristics
Solution Approach 1:
The patent achieves universality by developing a correction methodology that functions across multiple test object classes simultaneously. The optimization-based approach determines correction parameters that are universally applicable to diverse component classes with different attenuation characteristics. The cost function is formulated to account for variations across different test objects, enabling a single correction function to accurately correct nonlinearities for all component classes without requiring class-specific parameters, thereby maintaining both simplicity and accuracy.
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
The method ensures that the correction functions converge to a single optimal solution, reducing systematic errors and improving measurement accuracy by using a set of parameter values or parameter sets to determine correction functions independently of user-selected parameters.
Implementation Method 1
Beam hardening occurs in computed tomography with polychromatic x-ray sources in particular, since the low-energy part of the x-ray spectrum experiences a stronger attenuation during the passage through a test object than the higher energy part.
Implementation Method 2
In addition to the beam hardening, stray radiation also leads to further nonlinearities, especially in a computed tomography device
Data Source
AI summary
A method for correcting nonlinearities of image data of at least one radiograph and a computed tomography device are provided. The method includes obtaining image data of the at least one radiograph by irradiating an object with polychromatic invasive radiation and by detecting attenuated radiation that has passed through the object, utilizing a plurality of correction functions for correction purposes, said correction functions each being determined by the parameter value of at least one correction parameter, and applying an ascertainment method to ascertain the parameter value or the parameter values of the correction function used for correction purposes, said ascertainment method being determined by the parameter value of an ascertainment parameter or the parameter value sets of a plurality of ascertainment parameters.