Empirical Beam Hardening Correction for CT Imaging
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Solution Overview
Problem
Conventional computed tomography (CT) and differential phase contrast imaging (DPCI) techniques face challenges in accurately correcting beam hardening artifacts, which affect the accuracy of image data due to the polychromatic nature of X-ray sources and energy-dependent attenuation.
Innovation Solution
A beam hardening correction method that combines correction values with phase gradient or small angle scattering data, computed from attenuation data using a polynomial function to approximate the mean energy growth, allowing for empirical correction without requiring explicit knowledge of the X-ray spectrum or detector efficiency, and involves a calibration step using phantom data to determine coefficients for the correction function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If beam hardening correction is performed using conventional methods, then cupping and shading artifacts are reduced, but the correction requires explicit knowledge of the X-ray spectrum and detector efficiency which increases system complexity
Solution Approach 1:
The patent uses a polynomial function with empirically determined coefficients as a simplified, computationally inexpensive model to replace complex spectral analysis. This polynomial approximation acts as a 'cheap' correction method that achieves sufficient accuracy without requiring detailed knowledge of the X-ray spectrum or detector efficiency characteristics.
Solution Approach 2:
The patent transforms the correction approach by changing from a physics-based spectral model to an empirical parameter-based polynomial model. The coefficients of the polynomial are determined through calibration and then used to correct beam hardening effects, simplifying the problem from requiring full spectral knowledge to using simple polynomial parameters.
2Productivity
If beam hardening correction uses polynomial approximation of mean energy growth, then correction speed increases and spectral analysis is avoided, but the accuracy depends on the polynomial degree and calibration quality
Solution Approach 1:
The patent applies a polynomial approximation that captures the essential behavior of mean energy growth without modeling all spectral details. By using a polynomial of sufficient degree (typically 2-6 as mentioned in the patent), the method achieves adequate accuracy for practical purposes while maintaining computational efficiency, applying just enough correction complexity to solve the problem.
Solution Approach 2:
The patent performs calibration in advance to determine the polynomial coefficients that best fit the specific imaging system's beam hardening characteristics. This preliminary action stores the system-specific correction parameters, allowing rapid correction during actual imaging without repeating complex spectral analysis, thus achieving both speed and accuracy.
3Device complexity
If empirical correction method is used without explicit spectral knowledge, then device complexity is reduced and calibration is simplified, but the correction may not account for all beam hardening effects accurately
Solution Approach 1:
The patent makes the correction system self-calibrating by using phantom data acquired with the actual imaging system to determine the polynomial coefficients. This self-service approach allows the system to automatically adapt to its own beam hardening characteristics without requiring external spectral measurements or complex detector efficiency characterization, achieving reliability through system-specific calibration.
Solution Approach 2:
The calibration process uses measured phantom data to determine optimal polynomial coefficients, creating a feedback loop where the system's actual performance informs the correction parameters. This feedback mechanism ensures the empirical model accurately reflects the specific imaging system's beam hardening behavior, improving reliability despite the simplified approach.
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 method effectively corrects beam hardening artifacts in tomographic image data, providing accurate estimates of material traversed by the X-ray beam, reducing cupping and shading artifacts, and enabling precise image reconstruction without the need for complex spectral analysis.
Implementation Method 1
the X-ray attenuation depends strongly on energy of the X-ray beam
Implementation Method 2
Beam hardening is caused by the use of a polychromatic x-ray source and by the fact that the X-ray attenuation depends strongly on energy of the X-ray beam
Data Source
AI summary
A beam hardening correction method, a related calibration method for tomographic image data and a related apparatus. The tomographic image data includes attenuation data (f) and phase gradient data (g) and/or small angle scattering data (h). A correction value is computed from the attenuation data (f) by applying a function (q) to the attenuation data (f). The correction value is combined (S445) with the phase gradient data (g) or with the small angle scattering data (h).