CT Image Reconstruction Beam Hardening Scatter Removal
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Solution Overview
Problem
Computed tomography (CT) image reconstructions are affected by beam hardening and scatter artifacts, particularly when scanning metallic objects, leading to false features and inaccuracies in density measurements and feature representation.
Innovation Solution
A method that modifies the forward projection using a transfer function to remove beam hardening and scatter artifacts, applicable to any iterative CT image reconstruction algorithm, without requiring additional hardware or modeling the physics of these phenomena, and can be used to pre-correct scanner data for subsequent reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard CT reconstruction algorithms are used, then the reconstruction process is simple and fast, but beam hardening and scatter artifacts degrade image quality and measurement accuracy
Solution Approach 1:
The patent applies preliminary action by pre-correcting the scanner data to remove beam hardening and scatter artifacts before the reconstruction process. The correction involves calculating corrected projection data using the formula: p_corrected(θ, s) = p_measured(θ, s) × exp(μ₀ × L(θ, s)), where the correction factor is computed in advance based on the measured projection data and path length, then applied to eliminate artifacts before reconstruction.
Solution Approach 2:
The patent employs parameter changes by modifying the projection data parameters through the correction formula that adjusts the attenuation values. The correction transforms the measured projection data into corrected projection data by applying an exponential correction factor that compensates for beam hardening effects, thereby changing the data parameters to eliminate artifacts.
2Measurement precision
If hardware solutions like collimators are added to reduce scatter, then scatter artifacts are reduced, but the device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical hardware solution (collimators) with a computational/mathematical solution. Instead of adding physical collimator plates to block scattered X-rays, the patent applies a correction algorithm that mathematically removes scatter artifacts from the projection data using the correction formula, thereby eliminating the need for additional mechanical components.
Solution Approach 2:
The patent introduces an intermediary computational step between data acquisition and reconstruction. The correction algorithm acts as an intermediary that processes the measured projection data to remove artifacts before the final reconstruction, serving as a mathematical mediator that eliminates the need for physical scatter reduction hardware.
3Measurement precision
If iterative algorithms with physics modeling are used to remove artifacts, then image quality improves, but computational cost and processing time increase significantly
Solution Approach 1:
The patent extracts and removes the problematic beam hardening and scatter effects from the projection data before reconstruction. By separating the correction step from the main reconstruction algorithm and applying it preliminarily, the method eliminates artifacts without requiring complex iterative physics-based modeling during the reconstruction process itself, thereby maintaining computational efficiency.
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 removes beam hardening and scatter artifacts from CT images, improving the accuracy and quality of reconstructed images by integrating the transfer function into the iterative reconstruction process, allowing for scatter-free and accurate image generation.
Implementation Method 1
With beam hardening, a portion of the energy of the X-ray beam is absorbed by the object instead of just passing through it. The X-ray beam is polychromatic and the lower-energy X-rays are preferentially absorbed compared to the higher-energy X-rays.
Implementation Method 2
scatter, where part of the X-ray beam is deviated from its original input angle by free (or lossy) electrons within the object. As a consequence, part of the X-ray beam exits the object with a different angle, and thus incorrectly describes the object scanned.
Data Source
AI summary
A method for removing artifacts from an image reconstructed from scanner data according to embodiments includes: performing a forward projection p to update an estimated object image; determining a transfer function fθ that represents the effect of scatter and beam hardening; modifying the forward projection p using the transfer function fθ to provide a modified forward projection p′; and performing an iterative image reconstruction process using the modified forward projection p′ to generate a reconstructed image.