Edge-on Silicon X-ray Detector Modules with Anti-scatter Collimation
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Solution Overview
Problem
Silicon detectors used in x-ray imaging face challenges due to low atomic number and density, leading to inefficiency in high-energy applications and radiation-induced damage, which affects charge collection and image quality.
Innovation Solution
The detector system employs edge-on detector modules with an anti-scatter collimator made of high Z material to protect the front-side surfaces from direct x-ray radiation and scattered photons, and an anti-scatter foil to prevent radiation damage and misalignment artifacts, ensuring improved charge collection and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon detectors are made thicker to improve absorption efficiency for high energy x-rays, then detection efficiency improves, but radiation-induced damage increases
Solution Approach 1:
The detector is divided into multiple thin silicon layers (e.g., four 300 µm layers) rather than using a single thick layer. Each layer is independently depleted and read out, allowing the total detection path length to be increased while keeping individual layer thicknesses low enough to avoid excessive radiation damage accumulation in any single layer.
Solution Approach 2:
The invention transitions from a conventional planar detector geometry to a three-dimensional stacked configuration with edge-on readout. This dimensional change allows x-rays to traverse through multiple layers in sequence, increasing the effective detection thickness without proportionally increasing the damage exposure of any single readout surface.
2Ease of manufacture
If silicon detectors are used for high energy x-ray imaging, then material availability and charge carrier mobility are improved, but absorption efficiency deteriorates due to low atomic number and density
Solution Approach 1:
Multiple thin silicon layers are stacked to achieve the equivalent absorption of a single thick detector, maintaining silicon's advantages while compensating for its low absorption efficiency at high energies through increased interaction probability across multiple layers.
Solution Approach 2:
The detector combines silicon detection layers with high-Z anti-scatter foils (such as tungsten or lead) positioned between layers or at the rear. This composite structure leverages silicon's excellent charge carrier properties for signal generation while using high-Z materials to enhance x-ray absorption and reduce Compton scattering.
3Ease of manufacture
If conventional planar silicon detectors are used, then manufacturing is simplified, but radiation damage to the front surface increases due to direct x-ray exposure
Solution Approach 1:
The readout surface is inverted from the conventional front-side illumination geometry to an edge-on configuration. This inversion protects the sensitive front surface (with its passivation layer) from direct x-ray exposure while maintaining full detection capability through the edge-oriented electrode structure.
Solution Approach 2:
A collimator structure is introduced as an intermediary element positioned between the x-ray source and the detector. The collimator defines the x-ray beam geometry and prevents scattered photons from reaching the detector surface, thereby reducing radiation damage to the front surface while allowing necessary x-rays to pass through.
4Object-affected harmful factors
If anti-scatter foils are added to reduce Compton scattering, then scattered photon interference is reduced, but geometrical efficiency and charge collection may be affected
Solution Approach 1:
Anti-scatter foils are selectively positioned only in specific regions where Compton scattering is most problematic (such as between detector layers or at the rear), rather than uniformly across the entire detector. This localized approach reduces scattered photon interference while minimizing the impact on geometrical efficiency and charge collection in the active detection regions.
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 the robustness of silicon detectors against x-ray radiation, reducing surface damage and maintaining geometrical efficiency, thereby improving charge collection efficiency and image quality in x-ray imaging applications.
Implementation Method 1
an anti-scatter collimator made of high Z material to protect the front-side surfaces from direct x-ray radiation and scattered photons
Implementation Method 2
the radiation created charge carriers electron-hole pairs can be collected by the corresponding charge collecting electrodes
Implementation Method 3
By implanting heavily doped layers as electrical contacts on top of low doping silicon and by applying a reverse bias to the junction to make the detector fully depleted, the radiation created charge carriers electron-hole pairs can be collected
Implementation Method 4
The low atomic number also means the fraction of Compton scattered x-ray photons in the detector will dominate over the Photo absorbed photons
Implementation Method 5
which will create problem with the scattered photons since they may induce signals in other pixels in the detector
Data Source
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AI summary
Disclosed is a detector system for x-ray imaging. The detector system comprises a detector having a plurality of edge-on detector modules. Each of the edge-on detector modules comprises a first edge that is adapted to be oriented towards an x-ray source and a front-side running essentially parallel to the direction of incoming x-rays. The front-side comprising at least one charge collecting electrode. At least a subset of the plurality of edge-on detector modules being pairwise arranged, front-side to front-side, whereby a front-side to front-side gap is defined between the front-sides of said pairwise arranged edge-on detector modules. The pairwise arranged edge-on detector modules are associated with an anti-scatter collimator arranged in the x-ray path between the x-ray source and the edge-on detector modules and overlapping the front-side to front-side gap.