Dynamic X-Ray Beam Shaper for CT Intensity Modulation
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Solution Overview
Problem
Conventional bowtie filters in CT scanners have limited performance due to insufficient intensity modulation, beam hardening, and scattering issues, which degrade image quality and increase patient dose, and are not adaptable to varying subject shapes and positions.
Innovation Solution
A beam shaper system using high-Z materials like tungsten with elongate x-ray absorbing elements and material-free regions, which dynamically adjusts the intensity profile to maintain high intensity near the central ray and minimize scatter, allowing for flexible configuration to fit within the scanner and accommodate varying subject shapes and positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional bowtie filter is used to shape the radiation beam intensity profile, then the beam intensity is modulated to some extent, but the intensity modulation is insufficient (only about 15% at thicker portions) and the filter size must be large (at least 50mm thickness) which limits the examination region size
Solution Approach 1:
The beam shaper is divided into multiple independently controllable beam shapers that can be positioned at different locations. Each beam shaper can be independently adjusted to create the desired intensity profile, allowing for more aggressive modulation without requiring a single large filter structure that would limit the examination region.
Solution Approach 2:
The beam shapers are made movable and repositionable rather than fixed. This dynamic capability allows the system to adapt the beam intensity profile to different examination scenarios and subject sizes, achieving high modulation ratios while maintaining flexibility in the examination region size.
2Illumination intensity
If a bowtie filter is used to attenuate the beam, then the intensity profile is shaped, but beam hardening occurs which changes the x-ray spectrum and reduces dose efficiency
Solution Approach 1:
Different portions of the beam shaper are made with different materials having different atomic numbers. The first beam shaper uses a first material with a first atomic number while the second beam shaper uses a second material with a second atomic number. This local differentiation allows optimization of beam hardening characteristics in different regions, improving dose efficiency while maintaining intensity profile shaping capability.
3Illumination intensity
If a bowtie filter is used to attenuate the beam, then the intensity profile is shaped, but scattered radiation is generated which produces artifacts and degrades image quality
Solution Approach 1:
The beam shaper employs composite material structures with different atomic numbers arranged in specific configurations. The combination of materials with different Z values allows the system to shape the beam intensity profile while minimizing scatter generation, as each material layer can be optimized for its specific function of either attenuation or scatter reduction.
4Device complexity
If a fixed bowtie filter profile is used, then the filter design is simple, but it cannot adapt to varying subject shapes and positions which results in suboptimal intensity profiles
Solution Approach 1:
The beam shapers are designed to be movable and repositionable rather than fixed. This dynamic capability allows the system to adapt the beam intensity profile to different examination scenarios and subject sizes, achieving high modulation ratios while maintaining flexibility in the examination region.
Solution Approach 2:
The movable beam shaper configuration provides universal applicability across different subject types and examination scenarios. The same basic system can be reconfigured to handle various subject profiles (cylindrical, elliptical, off-center positions) by adjusting the beam shaper positions, eliminating the need for multiple specialized filters.
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 beam shaper achieves near 100% intensity at the central region and minimal intensity at peripheral regions with little to no scatter, maintaining optimal beam spectrum and improving image quality while accommodating diverse subject geometries without increasing patient dose.
Implementation Method 1
high-Z materials like tungsten with elongate x-ray absorbing elements
Implementation Method 2
a low 'Z' (atomic number) material. However, using a low 'Z' material reduces dose efficiency. Furthermore, a low 'Z' bowtie filter 102 attenuates heavily via the Compton effect, which generates scattered radiation
Data Source
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AI summary
An imaging system (500) includes a focal spot (510) that rotates along a path around an examination region (506) and emits radiation. A collimator (512) collimates the radiation, producing a radiation beam (516) that traverses a field of view (520) of the examination region and a subjector object therein. A detector array (522), located opposite the radiation source, across the examination region, detects radiation traversing the field of view and produces a signal indicative of the detected radiation. A beam shaper (524), located between the radiation source and the collimator, rotates in coordination with the focal spot and defines an intensity profile of the radiation beam. The beam shaper includes a plurality of elongate x-ray absorbing elements (606) arranged parallel to each other along a transverse direction with respect to a direction of the beam, separated from each other by a plurality of material free regions (604).