X-ray Filter for CT Displaced Geometry
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Solution Overview
Problem
CT imaging systems with offset x-ray source and detector geometry experience inhomogeneous signal-to-noise ratio (SNR) distribution due to overlapping projection data, leading to increased x-ray dose for patients.
Innovation Solution
A method and apparatus for filtering x-ray beams using a filter positioned between the x-ray source and object, which absorbs a percentage of overlapping radiation to reduce x-ray dosage and achieve a more homogeneous SNR distribution in reconstructed images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If offset x-ray source and detector geometry is used to increase field of view, then field of view is improved, but signal-to-noise ratio homogeneity deteriorates due to overlapping projection data
Solution Approach 1:
The patent applies local quality by implementing a filter that selectively attenuates x-ray beams only in the overlapping region of the detector, while leaving non-overlapping regions unaffected. This creates spatially varying transmission characteristics that compensate for the inhomogeneous SNR distribution caused by offset geometry, thereby improving SNR homogeneity without compromising the extended field of view capability
2Area of stationary object
If overlapping projection data is used for reconstruction, then field of view is improved, but x-ray dose increases
Solution Approach 1:
The filter introduces local quality variations by being positioned to affect only the overlapping beam paths. This localized intervention reduces the excessive x-ray dose in overlapping regions while preserving the necessary projection data for maintaining an extended field of view, thus resolving the contradiction between dose reduction and FOV preservation
Solution Approach 2:
The patent converts the harmful effect of overlapping beams (excessive dose) into a beneficial outcome by using the overlap region identification to strategically place filters. The previously harmful overlapping data, which caused inhomogeneous SNR and excessive dose, is now utilized to define precise filter locations that reduce dose while maintaining imaging quality
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 filter reduces x-ray dosage by up to 50% and provides a more homogeneous SNR distribution, improving image quality by balancing x-ray exposure across the image, allowing for effective scanning with reduced radiation exposure.
Implementation Method 1
A method and apparatus for filtering x-ray beams using a filter positioned between the x-ray source and object, which absorbs a percentage of overlapping radiation
Data Source
AI summary
A method and apparatus are provided to filter x-ray beams generated using a CT apparatus or other x-ray based system with displaced acquisition geometry. A CT apparatus may be used having a source (102), a detector (104) transversely displaced from a center (114) of a field of view (118) during acquisition of the projection data, and a filter (146). The filter may absorb at least a portion of overlapping radiation emitted by the source at opposing angular positions. The amount of transverse displacement may be determined for a desired field of view configuration and amount of overlapping radiation. The detector may be adjusted to correspond to the amount of determined transverse displacement. The size and location of the filter may be determined based on the amount of overlapping radiation. The filter may be adjusted to correspond to the determined size and location of the filter.