Tungsten Gradient Filter for X-ray Heel Effect Compensation
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Solution Overview
Problem
Existing CT imaging systems face significant heel effect issues due to cone-angle dependent variations in X-ray intensity and spectrum, leading to detector row dependent beam hardening and intensity variations, which current filters cannot fully correct, especially for 256 row detectors.
Innovation Solution
A thin filter made of the same material as the anode plate, such as tungsten, is positioned on the X-ray tube window, with a thickness gradient to compensate for the heel effect by varying the attenuation of X-rays, using techniques like sputtering or epitactical processes for precise deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a filter made of aluminum, copper, titanium or beryllium is used to compensate heel effect, then beam intensity uniformity is improved, but spectral distortion correction is insufficient
Solution Approach 1:
The invention changes the material parameter of the filter from conventional materials (aluminum, copper, titanium, beryllium) to tungsten, which has different attenuation characteristics. This material parameter change enables simultaneous correction of both intensity non-uniformity and spectral distortion, as tungsten's high atomic number and specific attenuation coefficients allow it to address both issues that previous materials could not resolve together.
Solution Approach 2:
The filter is constructed as a composite structure with a tungsten base material and a gradient layer containing iodine or gadolinium. This composite material approach combines the high attenuation properties of tungsten with the specific spectral interaction properties of the gradient materials, enabling comprehensive correction of both intensity and spectral variations across the detector array.
2Manufacturing precision
If a thin filter made of anode material is used to correct spectral distortions, then spectral uniformity is improved, but the filter thickness must be very small making production difficult
Solution Approach 1:
The filter implements local quality through a gradient structure where the concentration of iodine or gadolinium varies continuously from one side to the other. This gradient design allows different regions of the filter to provide different levels of attenuation, correcting spectral distortions across the field of view while maintaining manufacturability through controlled deposition or infiltration processes rather than requiring uniformly thin construction.
Solution Approach 2:
The invention adds a compositional dimension to the filter design by incorporating a gradient of iodine or gadolinium concentration within the tungsten matrix. This transforms the filter from a simple thin uniform layer into a three-dimensional structure with spatially varying composition, enabling spectral correction without relying solely on reducing thickness to the minimum possible value.
3Illumination intensity
If conventional filters are used, then beam intensity compensation is achieved, but detector row dependent beam hardening artifacts remain
Solution Approach 1:
The invention changes the attenuation parameters of the filter by using tungsten with specific gradient concentrations of iodine or gadolinium. This parameter change allows the filter to match the spectral characteristics required to compensate for beam hardening effects that cause artifacts, while simultaneously providing intensity uniformity across the detector array that conventional filters cannot achieve.
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 solution effectively compensates for the heel effect, providing a more uniform X-ray spectrum and intensity, reducing image artifacts by carefully controlling the filter's thickness gradient, specifically designed for CT imaging systems with 256 row detectors.
Implementation Method 1
X-rays traveling toward the anode side of an object being scanned travel through more volume of the target than X-rays traveling toward a cathode side of the object. Therefore, X-rays traveling toward the anode side leave the target more attenuated than X-rays traveling toward the cathode side.
Implementation Method 2
The production process of such a filter could be facilitated with some form of carefully controlled thin film deposition technique like sputtering or some other epitactical process.
Implementation Method 3
The production process of such a filter could be facilitated with some form of carefully controlled thin film deposition technique like sputtering or some other epitactical process.
Data Source
AI summary
It is described a filter (300) for at least partially compensating for an X-ray tube (10) the target angle heel effect and preserving the tungsten spectrum of the X-rays. The filter (300) has an anode side (302) and a cathode side (304), wherein the cathode side (304) has a higher attenuation coefficient than the anode side (302). The attenuation coefficient is determined to at least partially compensate for the target angle heel effect. The filter (300) is from the same material as an anode plate (110) or the anode (108) of the X-raysource (10) which is usually tungsten or a tungsten alloy.