X-ray System Calibration via Kinematic Model Optimization
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Solution Overview
Problem
Current methods for calibrating X-ray systems, particularly in computed tomography, face challenges in precision due to the complexity of axis systems with multiple degrees of freedom, where traditional calibration approaches are limited by assumptions about the axis system's accuracy and require direct accessibility or high precision manufacturing, which is not feasible for X-ray tube and detector components.
Innovation Solution
A method that creates a complete kinematic model of the X-ray system based on measured X-ray projections using Denavit-Hartenberg or similar representations, allowing for the determination of kinematic parameters by minimizing an error measure through non-linear optimization, enabling precise calibration of the system without relying on assumptions about the axis system's accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional calibration methods are used with fixed trajectories and reference bodies, then limited degrees of freedom can be determined, but the method is not suitable for complex systems with multiple degrees of freedom and freely positioned manipulators
Solution Approach 1:
The patent replaces traditional mechanical calibration approaches (fixed trajectories, tactile access, laser measurement) with a comprehensive mathematical model based on X-ray projection geometry. The system uses a complete kinematic model that can handle any trajectory type (circular, helical, or free-space motion) by formulating and solving a system of non-linear equations derived from projection geometry, enabling precise calibration of all degrees of freedom without mechanical constraints.
2Measurement precision
If manual adjustment and verification methods are used, then axis system configuration can be determined, but the process is time-consuming and requires painstaking adjustment
Solution Approach 1:
The calibration system performs self-calibration by automatically capturing X-ray projections at multiple positions, computing the complete kinematic model through mathematical optimization, and determining all axis system parameters without requiring manual intervention for adjustment or verification. The system solves the calibration problem autonomously by minimizing the difference between measured and computed projection data through non-linear optimization algorithms.
3Ease of manufacture
If assumptions about axis system accuracy are made, then calibration can be simplified, but the calibration quality is limited by these assumptions
Solution Approach 1:
The patent fundamentally changes the calibration approach by not assuming any predefined accuracy or configuration of the axis system. Instead, it treats all kinematic parameters as unknowns to be determined through the mathematical model. The system formulates a complete set of non-linear equations based on projection geometry and solves for all parameters simultaneously, eliminating the need for simplifying assumptions and achieving high calibration quality regardless of initial system precision.
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 approach enables accurate calibration of complex X-ray systems by generating a comprehensive kinematic model from X-ray projections, improving calibration quality and precision, and is applicable to systems with multiple degrees of freedom, including those with freely positioned robots and complex trajectories.
Implementation Method 1
determining an X-ray projection of the calibration object for the first position on the motion trajectory
Data Source
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AI summary
A method for calibrating an X-ray system with a radiation source and a radiation detector comprises the steps of determining a kinematic model for at least one position, defining initial values, calibrating, and solving a system of equations by minimization. The system of equations is derived from the determined kinematic model of the X-ray system. This system includes kinematic parameter sets for each position and parameters to be calibrated, which are typically the same across all positions. In the initial value setting step, these parameters to be calibrated are defined. Based on these initial values, at least one image is acquired using calibration blocks during the calibration step. A comparison of the measurement results with the respective references yields an error measure. This error measure is minimized when solving the system of equations.