X-ray CT Calibration Apparatus with Kinematically Locked Spheres
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Solution Overview
Problem
X-ray computed tomography (CT) systems lack well-defined verification standards and gauging tools for accurate calibration, leading to potential inaccuracies in measurements, which can have catastrophic effects in applications like aircraft and medical devices.
Innovation Solution
A calibration apparatus comprising a base and multiple x-ray visible objects, kinematically constrained to maintain precise positioning without external locking components or adhesives, ensuring accurate and stable measurements by forming a straight line with minimal deviation, allowing for precise calibration and verification of CT machines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional CT systems are used for coordinate metrology, then imaging capability is provided, but verification standards and gauging tools are lacking leading to measurement inaccuracy
Solution Approach 1:
The calibration apparatus is designed to be self-contained with all necessary calibration features integrated into a single device. The apparatus includes multiple spheres with known precise spacing that can be imaged by the CT system to perform self-verification of measurement accuracy without requiring external calibration equipment or complex verification procedures.
Solution Approach 2:
The apparatus uses materials with different x-ray attenuation coefficients (such as aluminum, copper, and tungsten spheres) that appear as distinct densities in CT images. This allows the calibration features to be clearly differentiated and measured, providing visual contrast that enables accurate measurement verification.
2Measurement precision
If discrete markers are embedded in supporting structure, then calibration is enabled, but positioning accuracy of markings is limited
Solution Approach 1:
Instead of using a continuous supporting structure with embedded markers, the invention uses multiple discrete spheres that are independently positioned. Each sphere serves as an independent calibration feature with its position determined by precise mechanical spacing structures, allowing individual verification and reducing cumulative positioning errors.
Solution Approach 2:
The invention replaces traditional mechanical marking systems with x-ray visible spherical features that are measured through CT imaging. The calibration is achieved by measuring the distances between sphere centers in 3D space, substituting physical markings with volumetric geometric features that can be measured with higher precision through computational methods.
3Stability of the object's composition
If objects are fixedly supported with external locking components or adhesives, then positioning stability is improved, but imaging interference occurs
Solution Approach 1:
The invention extracts and eliminates external locking components and adhesives from the calibration apparatus design. Instead, the spheres are retained through their own geometry and the CT imaging process itself, allowing the calibration features to be imaged without interference from retaining structures. The spheres are freely positioned within the field of view without requiring physical attachment.
Solution Approach 2:
The invention introduces a vacuum field as an intermediary medium to hold the spherical features in place during imaging. The vacuum environment prevents convection currents and physical contact with support structures, allowing the spheres to be positioned and imaged without mechanical retention systems that would interfere with the x-ray imaging process.
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 solution enables highly accurate calibration and verification of CT systems, ensuring measurements with sub-millimeter precision, reducing uncertainty and improving the reliability of dimensional measurements in CT imaging.
Implementation Method 1
Each one of the plurality of objects: 1) is configured to receive x-rays without changing shape, 2) has substantially the same shape and size as the other objects, 3) has an attenuation value to x-rays ('object attenuation value'), and 4) is symmetrically shaped relative to its center point. Like the base, the base also has an attenuation value to x-rays (the 'base attenuation value'). The object attenuation value is greater than the base attenuation.
Data Source
Figure 1A
Figure 1B
Figure 2~3
AI summary
An apparatus for calibrating an x-ray computed tomography device has a plurality of objects formed from a material that is visible to x-rays, and a base at least in part fixedly supporting the plurality of objects so that each of the plurality of objects contacts at least one of the other objects. Each one of the plurality of objects: 1) is configured to receive x-rays without changing shape, 2) has substantially the same shape and size as the other objects, 3) has an attenuation value to x-rays ("object attenuation value"), and 4) is symmetrically shaped relative to its center point. Like the objects, the base also has an attenuation value to x-rays (the "base attenuation value"). The object attenuation value is greater than the base attenuation. Each of the plurality of objects is kinematically locked in place on the base.