Perforated High-Z X-ray Attenuator for Beam Hardening
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Solution Overview
Problem
Conventional X-ray imaging devices face challenges with bow tie filters, which are space-consuming and cause beam hardening, leading to uneven X-ray intensity distribution and image quality issues due to varying X-ray absorption across the detector plane.
Innovation Solution
An X-ray emitting device with a perforated sheet of high atomic number material featuring pinhole openings, denser at the center than the periphery, providing varying transparency to achieve a beneficial X-ray intensity distribution while being compact and spectrally neutral, and allowing for adjustable X-ray transmission by displacing individual sheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional bow tie filter is used to smoothen photon flux across the detector, then X-ray intensity distribution is improved, but the filter occupies valuable space and causes beam hardening
Solution Approach 1:
The patent applies a perforated sheet with pinhole openings in a high-Z material. This porous structure allows X-rays to pass through selected regions while blocking others, achieving intensity modulation without requiring a solid filter mass. The pinholes act as transmission channels that can be strategically positioned and sized to control the X-ray flux distribution across the detector plane.
Solution Approach 2:
The patent changes the material parameter from low-Z (conventional bow tie filter) to high-Z material. This parameter change enables much higher X-ray attenuation per unit thickness, allowing the filter to achieve the same intensity modulation effect with dramatically reduced thickness and volume. The high-Z material's superior attenuation properties eliminate the need for thick filter structures.
2Illumination intensity
If a conventional bow tie filter is used to smoothen photon flux, then X-ray intensity distribution is improved, but beam hardening occurs which deteriorates image quality
Solution Approach 1:
The perforated sheet structure allows selective transmission of X-ray beams through pinholes while maintaining the ability to preserve spectral composition. By using high-Z material with controlled pinhole geometry, the system achieves intensity modulation without the extensive path length through filter material that causes beam hardening in conventional designs.
Solution Approach 2:
The patent uses a composite approach combining high-Z material with a perforated structure. This composite design achieves both attenuation and spectral preservation: the high-Z material provides strong attenuation where needed while the pinhole geometry minimizes the overall interaction path length, reducing beam hardening effects compared to solid low-Z filters.
3Reliability
If a bow tie filter made from low-Z material is used, then spectral sensitivity is maintained, but the filter thickness must be large up to several cm
Solution Approach 1:
The patent fundamentally changes the material parameter from low-Z to high-Z. High-Z materials have much higher X-ray attenuation coefficients, enabling the same filtering effect to be achieved with thickness reduced from several cm to potentially mm or sub-mm scales. This parameter change reverses the traditional relationship where low-Z materials required large thickness.
Solution Approach 2:
The perforated structure provides an additional mechanism for controlling effective thickness. By creating void spaces (pinholes) through the high-Z material, the system reduces the actual path length X-rays must traverse through attenuating material, further reducing the overall component thickness while maintaining spectral properties.
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 ensures a more uniform X-ray intensity distribution, reduces beam hardening, and minimizes space requirements, improving image quality and workflow in X-ray imaging devices by allowing for adaptable X-ray transmission patterns.
Implementation Method 1
Materials with low atomic number (Z) are preferred. The photoelectric effect, which is the dominating and highly spectral sensitive physical effect of attenuation for materials with high atomic numbers, is small for these low-Z-materials.
Implementation Method 2
For low-Z-materials the Compton scatter effect takes over, which is a less spectral sensitive effect of attenuation in the range of photon energies, which are relevant for human CT.
Data Source
AI summary
An X-ray emitting device (200) with an attenuating element (1) for an X-ray imaging device (100) is proposed. The attenuating element comprises a perforated sheet (3) of strongly X-ray absorbing material such as e.g. tungsten or molybdenum with a sheet thickness of e.g. less than 1 mm. The sheet (3) comprises multiple pinhole openings (5). Therein, a density of pinhole openings is higher at a center region of the sheet than at border regions of the sheet. Accordingly, a transparency to X-rays is higher at the center region than at the border regions. The pinhole openings (5) have geometries such that most parts of contours of the pinhole openings are non-parallel to edges of a focal spot (15) of an X-ray source (101) comprised in the X-ray emitting device. For example, the pinhole openings may have a circular, oval or any other cross-sectional geometry with non-linear edges. In an X-ray imaging device, such attenuating element may avoid beam hardening, needs less space than a conventional bow tie filter and is relatively insensitive to focal spot shifts.