Grating Pitch Variation for Phase Contrast CT
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Solution Overview
Problem
Conventional grating-based phase contrast computed tomography systems face significant challenges with large fan angles, leading to reduced structure visibility and the need for complex curved or tilted detectors, which are difficult to manufacture and maintain, especially in medical applications where larger fan angles are required.
Innovation Solution
The source-detector arrangement is modified by orienting the grating elements and the X-ray source line pattern orthogonal to the rotation axis, with varying grating pitches dependent on the cone angle of the X-ray beam, allowing for the use of planar detectors and maintaining high X-ray flux, even at shallow anode angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the fan angle of the X-ray beam is increased to accommodate large objects in medical applications, then the coverage area is improved, but the structure visibility is reduced
Solution Approach 1:
The grating pitch is made variable across different regions of the detector, with each region having a pitch optimized for its specific cone angle. This local adaptation of the grating structure allows the system to maintain high structure visibility in each local area while collectively covering a large fan angle for big objects.
Solution Approach 2:
The grating pitch parameter is changed as a function of the cone angle. By varying the grating pitch according to the local cone angle across the detector surface, the system maintains optimal interference patterns and structure visibility for each angular region, thereby preserving measurement precision across the entire large fan angle range.
2Area of stationary object
If conventional grating-based phase contrast imaging is used with large fan angles, then the coverage is improved, but the detector complexity increases due to the need for curved or tilted detectors
Solution Approach 1:
Instead of making the entire detector curved or tilted, the invention applies a locally optimized grating pitch only where needed. The detector itself remains flat and simple, but each region has a grating element with a pitch tailored to its specific cone angle, achieving local optimization without global complexity.
Solution Approach 2:
The grating pitch parameter is varied across the detector surface according to the cone angle, allowing a simple flat detector geometry to achieve the performance that would otherwise require complex curved or tilted detector designs. This parameter variation in the grating element substitutes for geometric complexity in the detector.
3Ease of manufacture
If the grating pitch is kept constant, then the manufacturing is simplified, but the structure visibility deteriorates at varying cone angles
Solution Approach 1:
The grating element is designed with locally varying pitch rather than a uniform pitch. Each local region has a pitch optimized for its specific cone angle, which maintains structure visibility across the entire detector surface while still being manufacturable as a single integrated component.
Solution Approach 2:
The grating pitch parameter is made variable across the grating surface, changing according to the local cone angle. This parameter variation allows the grating to maintain optimal performance for structure visibility at all angles, while the entire grating can still be manufactured as one piece using modern fabrication techniques.
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 configuration enhances structure visibility and reduces the complexity of detector systems, enabling effective phase-contrast imaging with larger fan angles without the need for curved or tilted detectors, improving image quality and system simplicity.
Implementation Method 1
Grating based phase contrast imaging systems further provide dark field images which are indicative for the small angle scattering power of the sample
Implementation Method 2
at least partly spatially coherent or quasi coherent radiation in a line pattern is employed. Coherent or quasi coherent X-rays penetrating the object may allow for subsequent retrieval of phase information
Implementation Method 3
Radiation emanating from the X-ray source is penetrating the object to be examined, subsequently arriving at the X-ray detection system
Implementation Method 4
an X-ray detection system including a first grating element and a second grating element and a detector element
Data Source
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AI summary
The invention relates to a source-detector arrangement (11) of an X-ray apparatus (10) for grating based phase contrast computed tomography. The source-detector arrangement comprises an X-ray source (12) adapted for rotational movement around a rotation axis (R) relative to an object (140) and adapted for emittance of an X-ray beam of coherent or quasi-coherent radiation in a line pattern (21); and an X-ray detection system (16) including a first grating element (24) and a second grating element (26) and a detector element (6); wherein the line pattern of the radiation and a grating direction of the grating elements are arranged orthogonal to the rotation axis; and wherein the first grating element has a first grating pitch varied dependent on a cone angle (β) of the X-ray beam and/or the second grating element has a second grating pitch varied dependent on the cone angle of the X-ray beam.