3D-beam modulation filter for breast CT dose equalization
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Solution Overview
Problem
Conventional computed tomography (CT) systems for breast imaging do not account for the actual shape or size of the breast, leading to inhomogeneous x-ray beam intensity and higher radiation doses anteriorly relative to posteriorly, resulting in suboptimal image quality and radiation distribution.
Innovation Solution
A 3D-beam modulation filter that modulates the x-ray beam in both cone and fan angles to equalize photon fluence, reducing radiation doses to anterior and peripheral regions while maintaining image quality, and is designed based on specific breast shapes and sizes using a cohort of breast volume datasets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a uniform x-ray beam distribution is used in conventional CT systems, then the system is simple to operate, but the radiation dose is higher anteriorly and the image quality is suboptimal due to inhomogeneous beam intensity
Solution Approach 1:
The patent applies local quality by creating a 3D beam modulation filter with spatially varying attenuation properties. The filter is designed with different attenuation coefficients at different locations (anterior vs posterior, central vs peripheral) to compensate for the varying thickness of breast tissue. This allows the x-ray beam to be locally adjusted to achieve uniform photon fluence across the detector, reducing radiation dose in anterior regions while maintaining adequate penetration in posterior regions.
2Reliability
If conventional bowtie filters are used, then detector dynamic range is reduced, but the filter does not account for actual breast shape leading to suboptimal dose reduction
Solution Approach 1:
The patent transitions from conventional 2D bowtie filters to a 3D beam modulation filter that accounts for variations in both the fan angle direction and the cone angle direction. This third dimension (cone angle) is crucial for breast CT imaging as it allows the filter to adapt to the actual 3D shape of the breast, providing optimized dose reduction throughout the entire volume rather than just at the detector plane.
Solution Approach 2:
The filter design involves changing multiple parameters including attenuation coefficients, filter thickness, and spatial distribution to optimize both detector dynamic range and radiation dose reduction. The attenuation properties are specifically tailored to match the breast anatomy, with higher attenuation in anterior regions and lower attenuation in posterior regions.
3Ease of manufacture
If the x-ray beam is attenuated uniformly, then the system is simple to implement, but image quality deteriorates due to beam hardening effects and non-uniform signal at the detector
Solution Approach 1:
The 3D beam modulation filter is designed and positioned in advance to pre-compensate for the varying path lengths through breast tissue. By performing the attenuation modulation before the x-ray beam enters the breast, the system achieves uniform photon fluence at the detector without requiring complex post-processing corrections for beam hardening or non-uniform signal distribution.
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 3D-beam modulation filter reduces unnecessary radiation exposure and improves image quality by compensating for breast thickness variations, achieving a more uniform signal at the detector and reducing radiation doses by up to 54% without compromising image quality.
Implementation Method 1
The filter attenuates x-ray intensity along the x-ray paths that are attenuated only slightly by the breast (i.e. anterior and peripheral regions of the breast), while attenuating much less of the x-ray intensity along the highly attenuating x-ray paths
Data Source
AI summary
A size and/or shape specific 3D-beam modulation filter and a size and/or shape specific immobilizer are provided for cone-beam breast computed tomography (bCT). The immobilizer places the breast on an optimal position in the field of view of the scanner system and the 3D-beam modulation filter modulates the incident x-ray beam in the cone-angle (i.e. z-axis of the detector panel) and fan angle (i.e. x-axis of the detector panel) directions in order to improve equalization of the photon fluence incident upon the detector panel and reduce unnecessary radiation dose that the breast receives. Both the immobilizer and the 3D-beam modulation filter are selected among a plurality of alternatives based on the specific shape, size and/or shape or size of the person's breast.