Variable Pitch Collimator for CT Scintillator Alignment
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Solution Overview
Problem
In computed tomography (CT) imaging systems, the fixed pitch of collimator plates leads to misalignment errors between the scintillator pack and the collimator, resulting in varying spectral performance and gain response, especially as the focal spot moves, affecting the accuracy of image reconstruction.
Innovation Solution
A variable pitch collimator assembly is designed with a curved rail and two sets of x-ray attenuation plates, where the first set is spaced by a first pitch and the second set by a second pitch greater than the first, optimizing the alignment and spectral performance of scintillator packs by varying the pitch between collimator plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fixed pitch collimator plates are used to simplify manufacturing, then manufacturing precision is improved, but alignment accuracy between scintillator pack and collimator deteriorates
Solution Approach 1:
The collimator plate pitch is changed from fixed to variable, allowing the pitch to dynamically adapt to the curved geometry of the collimator. This enables the collimator plates to maintain proper alignment with the scintillator pack channels across different positions, resolving the alignment accuracy issue while keeping manufacturing relatively simple through a systematic pitch variation pattern.
Solution Approach 2:
Different regions of the collimator have different pitch values tailored to their specific geometric requirements. The pitch varies locally to compensate for the curved surface geometry, ensuring that each local region maintains optimal alignment between collimator plates and scintillator channels, thereby improving overall alignment accuracy without requiring complex manufacturing throughout the entire structure.
2Ease of manufacture
If collimator pitch matches scintillator pack pitch, then manufacturing is simplified, but spectral performance uniformity deteriorates due to misalignment errors
Solution Approach 1:
The collimator pitch is dynamically adjusted across different positions rather than being uniformly matched to the scintillator pack pitch. This dynamic pitch variation compensates for the curved geometry of the collimator, maintaining proper alignment between collimator plates and scintillator channels throughout the detector array, thereby ensuring uniform spectral performance across all channels.
Solution Approach 2:
The pitch parameter of the collimator plates is changed from a constant value to a variable value that changes with position. This parameter change allows the system to maintain optimal alignment and spectral performance across different detector channels, preventing the degradation of spectral performance consistency that would occur with a fixed pitch matching the scintillator pack.
3Ease of manufacture
If collimator plates are aligned with center channels, then manufacturing alignment is easier, but edge channel performance deteriorates due to accumulated error
Solution Approach 1:
The pitch of collimator plates is locally optimized for different regions of the detector array. Rather than using a uniform pitch that causes accumulated errors at the edges, each local region has a pitch value specifically tailored to its position on the curved collimator surface. This local optimization ensures that alignment accuracy is maintained across all channels, including edge channels, preventing the degradation of measurement precision at the edges.
Solution Approach 2:
The collimator pitch varies dynamically across the detector array to compensate for positional differences. This dynamic pitch adjustment ensures that the alignment between collimator plates and scintillator channels is maintained uniformly across the entire array, eliminating the accumulated errors that would otherwise occur at edge channels and maintaining high measurement precision throughout.
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 design minimizes spectral non-linearity and ensures consistent spectral performance across all scintillator channels, enhancing the sensitivity and accuracy of image reconstruction by optimizing the alignment and edge coverage of the collimator plates.
Implementation Method 1
The post patient x-ray collimator used in CT detection is a device mainly made of a highly absorbing material such as tungsten or molybdenum plates or high-Z material alloy aligned to a focal spot on the x-ray tube. The main function of the collimator is to select x-rays along a particular direction (primary beam from focal spot) and to reject scattered radiation from other directions
Data Source
AI summary
An x-ray detector assembly includes a curved rail and a first plurality of x-ray attenuation plates attached to the curved rail, wherein the plates of the first plurality of x-ray attenuation plates are spaced apart from one another by a first pitch. A second plurality of x-ray attenuation plates are attached to the curved rail, wherein the plates of the second plurality of x-ray attenuation plates are spaced apart from the plates of the first plurality of x-ray attenuation plates by a second pitch greater than the first pitch. A first plurality of x-ray detector cells is also positioned adjacently to the first and second pluralities of x-ray attenuation plates and positioned in a linear arrangement with respect to each other.