Volumetric Imaging Calibration via Phantom Marker Analysis
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Solution Overview
Problem
Volumetric imaging systems face challenges in accurately determining critical alignment parameters, leading to suboptimal image quality due to imprecise geometrical calibration, especially in systems with less well-defined mechanics and synchronization, limiting their utility in applications like C-arm and tomosynthesis imaging.
Innovation Solution
A method for geometrical calibration of volumetric imaging systems involving the use of phantoms with discrete markers arranged in specific patterns, such as helical or elongated arrays, to compute projection errors and update imaging geometry parameters, enabling precise alignment and improved image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used for volumetric imaging systems, then the system can operate with simpler mechanics, but the geometrical calibration precision deteriorates leading to artifacts and blurring in reconstructed images
Solution Approach 1:
The patent applies preliminary action by performing geometrical calibration before actual imaging operations. A calibration phantom with known marker positions is scanned to determine accurate geometrical parameters (source position, detector position, rotation axis) before patient or object imaging. This ensures that the imaging system has precise calibration data ready for use, preventing artifacts and blurring in reconstructed images while maintaining operational simplicity during actual imaging tasks.
2Measurement precision
If direct measurement of alignment parameters is performed, then the calibration process becomes simpler, but the measurement precision deteriorates due to difficulty in making direct measurements on the acquisition system
Solution Approach 1:
The patent uses an intermediary approach by introducing a calibration phantom as a mediator between the imaging system and the calibration process. Instead of directly measuring alignment parameters on the acquisition system (which is difficult and imprecise), the phantom with known marker positions serves as an intermediary object that can be scanned to indirectly determine the geometrical parameters. This transfer of the measurement problem to a controlled phantom object significantly improves measurement precision while keeping the operation straightforward.
Solution Approach 2:
The patent applies copying by creating a simplified representation of the calibration problem through the phantom. The phantom contains simplified marker structures (such as spheres or rods) with known positions that replicate the essential geometrical information needed for calibration without the complexity of measuring the actual imaging system components. This copying approach transforms a difficult direct measurement problem into an easier indirect measurement problem while maintaining high precision.
3Reliability
If accurate geometrical parameters are determined for volumetric imaging, then image reconstruction quality improves, but the difficulty of detecting and measuring these parameters increases
Solution Approach 1:
The patent replaces complex mechanical measurement approaches with an optical/imaging-based approach. Instead of using mechanical instruments to directly measure source position, detector position, and rotation axis (which would be mechanically complex and difficult), the system uses radiation imaging of a phantom to determine these parameters. The known marker positions in the phantom create detectable patterns in the projection images that can be used to calculate geometrical parameters through computational methods, significantly reducing the difficulty of measurement while improving reliability.
4Measurement precision
If physical adjustment of component locations and orientations is performed, then the imaging system alignment improves, but the time required for calibration increases
Solution Approach 1:
The patent applies self-service by enabling the imaging system to perform its own calibration automatically. Instead of requiring manual physical adjustment of components followed by verification scanning, the system uses a calibration phantom with known marker positions and automated image processing to determine and correct geometrical parameters. The system self-diagnoses and self-corrects alignment issues through computational methods, eliminating the need for time-consuming manual adjustments while maintaining high 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 allows for more accurate determination of imaging geometry parameters, enhancing the quality of volumetric images by iteratively updating and refining the calibration, thereby improving the reliability of image reconstruction across a wider range of imaging geometries.
Implementation Method 1
The beam passes through the object being imaged, such as a patient. The radiation beam, after being attenuated by the object impinges upon a detector consisting of an array of detector elements. The intensity of the radiation received at the detector array is dependent upon the attenuation of the radiation beam by the object.
Data Source
AI summary
A technique is provided for geometrical analysis and calibration of a volumetric imaging system. The technique includes computing a projection error between estimated locations of a set of markers of a phantom based on a estimated imaging geometry and observed locations of the respective markers for at least one projection image, decomposing the computed projection error into one or more error components corresponding to respective geometric parameters of the imaging geometry, and updating at least one parameter of the estimated imaging geometry based on the one or more error components.