CT Image Heel Effect Compensation via Voxel Scaling
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Solution Overview
Problem
Current CT imaging methods suffer from the 'heel effect' artefact, which causes spectral variations in x-ray beams due to the angled anode, leading to distorted 3D images with abrupt contrast changes at object transitions, known as the 'bamboo effect', that are difficult to correct effectively.
Innovation Solution
A method that corrects 3D CT images by applying scaling factors to voxel slices based on calibration images of similar structures at different y-positions, compensating for the heel effect's spectral impact without requiring detailed knowledge of the measurement setup or object materials, using 3D CT calibration images to determine these scaling factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional CT imaging with angled anode is used, then x-ray generation efficiency is improved, but heel effect artefacts cause spectral variations leading to distorted 3D images with abrupt contrast changes
Solution Approach 1:
The patent applies preliminary action by determining scaling factors from calibration images before correcting the actual 3D CT images. The calibration images are acquired and processed in advance to establish the heel effect compensation parameters, which are then applied to correct the main imaging data, separating the correction process from the primary imaging workflow
Solution Approach 2:
The patent uses calibration objects with known structures to create copies or representations of how the heel effect manifests under controlled conditions. These calibration images serve as reference models that capture the spectral variations, allowing the system to learn and compensate for heel effect artefacts without requiring detailed knowledge of the actual object being imaged
2Measurement precision
If detailed knowledge of measurement setup and object materials is used for correction, then correction accuracy is improved, but device complexity and implementation difficulty increase
Solution Approach 1:
The system performs self-calibration by using the calibration images themselves to determine the scaling factors needed for correction. The calibration process is autonomous and does not require external intervention or detailed input about the measurement setup parameters or object materials, making the system self-sufficient and easier to implement
Solution Approach 2:
The patent changes the approach from using fixed physical parameters (anode angle, material composition) to using empirically determined scaling factors that are derived from calibration images. This parameter transformation allows the system to adapt to different measurement setups and objects without requiring detailed knowledge of their physical characteristics
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 simplifies the correction process, reduces artefacts like the bamboo effect, and improves image contrast uniformly across the 3D CT images, making it universally applicable and easier to implement compared to existing methods.
Implementation Method 1
The electrons somewhat penetrate the anode material and are slowed down in the anode material, what generates x-rays in the form of bremsstrahlung, having a basically continuous spectral range.
Implementation Method 2
The anode material attenuates the generated x-rays passing through it, what influences the characteristics of the generated x-ray beams; this phenomenon is called 'heel effect'.
Implementation Method 3
a 2D x-ray detector behind the object detects the x-ray intensity
Data Source
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AI summary
A method for obtaining a CT (= Computer Tomography) image (36, 53) of an object (10), with the following steps: a) generating x-rays (8) using an x-ray source (2) comprising an angled anode (3), b) recording at least one set (33) of 2D projections (31) of the object (10) or a part of the object (10), c) generating at least one 3D CT image (34) of the object (10); is characterized in that the method further comprises a step of d) for each generated 3D CT image (34), correcting the 3D CT image (34), wherein scaling factors (sf) for slices (64) of voxels are determined with at least one 3D CT calibration image (62) measured with the measurement setup (1), wherein the at least one 3D CT calibration image (62) pictures similar or identical object structures (64a, 64b; 71, 72) of a calibration object (61) placed within the beam path of the x-rays (8) in different regions (R1, R2) of a field of view (50) of the measurement setup (1) with respect to a y-direction, wherein for the at least one 3D CT calibration image (62) a grey value contribution to the grey values of voxels belonging to the similar or identical object structures (64a, 64b; 71, 72) in said different regions (R1, R2) attributable to the slice position (ns, js) in y direction is determined at least approximately, and the scaling factor (sf) for a respective slice (64) of voxels is chosen such that it compensates for the determined grey value contribution for that slice (64). The method reduces heel effect artefacts in a simple way.