Heel Effect Correction in CT Scanners via Anode Interaction Depth
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Solution Overview
Problem
Large Z-coverage CT scanners are prone to the heel effect, which causes non-uniformity in x-ray intensity and average energy as a function of detector row angle, negatively affecting image quality due to the geometry of the x-ray tube's anode.
Innovation Solution
A computer-implemented method and system for correcting CT data to account for the heel effect by using a heel correction factor based on the interaction depth of x-rays within the anode and their angular direction to specific pixels in the detector, allowing for accurate reconstruction of images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware filters are used to reduce beam hardening, then image quality improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces physical hardware filters with a software-based correction algorithm. The heel effect correction is implemented through computational processing of projection data, applying correction factors derived from the anode geometry and x-ray interaction depth, thereby eliminating the need for additional hardware filters while maintaining image quality.
Solution Approach 2:
The patent introduces an intermediary correction factor that mediates between the raw projection data and the final image reconstruction. This correction factor, calculated based on the interaction depth of x-rays within the anode and the angular direction to detector pixels, serves as a computational intermediary that compensates for beam hardening effects without requiring physical filter materials.
2Stability of the object's composition
If the anode geometry is changed to reduce heel effect, then x-ray intensity uniformity improves, but manufacturing precision requirements increase
Solution Approach 1:
Instead of modifying the anode geometry to achieve uniform x-ray intensity, the patent inverts the approach by keeping the anode geometry fixed and applying computational corrections to the projection data. The correction algorithm accounts for the heel effect by calculating interaction depth and angular direction factors, thereby achieving intensity uniformity through software rather than hardware modification.
3Productivity
If Z-coverage is increased in CT scanners, then scanning capability improves, but heel effect non-uniformity worsens
Solution Approach 1:
The patent addresses the heel effect in the Z-direction (detector row angle) by introducing a correction dimension that accounts for interaction depth within the anode and angular direction to specific detector pixels. This additional computational dimension allows the system to compensate for intensity variations across the extended Z-coverage range, enabling large Z-coverage scanning while maintaining image uniformity.
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
Improves image quality by correcting non-uniformity across image slices and channels, optimizing beam hardening correction, and reducing the need for hardware filters, leading to cost savings and enhanced CT number accuracy and uniformity.
Implementation Method 1
These detectors generally have scintillation crystal/photodiode arrays, where the scintillation crystal absorbs x-rays and converts the absorbed energy into visible light
Implementation Method 2
A photodiode is used to convert the light to an electric current
Implementation Method 3
an x-ray tube having an anode, the x-ray tube positioned on the gantry to generate x-rays from a focal spot on the anode
Implementation Method 4
X-rays emit from the x-ray tube, are attenuated by the patient
Data Source
AI summary
A CT system includes a rotatable gantry having an opening to receive an object to be scanned, an x-ray tube having an anode, the x-ray tube positioned on the gantry to generate x-rays from a focal spot of the anode and through the opening, and a pixelated detector positioned on the gantry to receive the x-rays. The system includes a computer programmed to acquire CT data based on x-rays passing through the opening and to the pixelated detector, generate projection data from the acquired CT data, the projection data is corrected to account for heel effect by a correction factor that is determined based in part on an interaction depth of the x-rays within the anode, and based on an angular direction from the interaction depth to particular pixels within the pixelated detector, and reconstruct an image based on the generated projection data.