Fluoroscope Image Distortion Correction via S-Distortion Modeling
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Solution Overview
Problem
Current electromagnetic navigation systems in medical applications, particularly those using fluoroscope cameras, face challenges with S-distortion caused by external magnetic fields, which affect navigation accuracy and require insufficient calibration methods, especially in 3D imaging and mobile settings.
Innovation Solution
A method and system for modeling and compensating S-distortion in image intensifiers by computing charged particle velocity and magnetic field vectors, and using an analytic S-distortion model for calibration, which involves identifying reference coordinates, computing magnetic field components, and updating intrinsic and extrinsic parameters to correct image distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an image intensifier is used in a fluoroscope to improve image visibility and reduce x-ray dose, then image intensity is improved, but S-distortion occurs due to earth's magnetic field affecting electron paths
Solution Approach 1:
The patent applies parameter changes by computing correction factors based on the position of the image intensifier relative to the C-arm fluoroscope. The system dynamically adjusts distortion correction parameters according to the IID's location, compensating for S-distortion caused by earth's magnetic field while maintaining the image intensifier's function of amplifying x-ray images.
2Adaptability or versatility
If electromagnetic tracking is used to navigate surgical tools in 3D space, then navigation capability is improved, but S-distortion varies with IID position reducing accuracy
Solution Approach 1:
The system implements feedback by continuously tracking the position of the image intensifier relative to the C-arm fluoroscope and using this information to dynamically compute and apply distortion correction factors. This closed-loop approach ensures that navigation accuracy is maintained despite variations in IID position and the resulting S-distortion.
3Ease of operation
If standard calibration methods are used for the fluoroscope camera, then calibration is simplified, but re-projection errors increase reducing navigation precision
Solution Approach 1:
The patent applies preliminary action by pre-computing distortion correction factors based on the modeled relationship between IID position and S-distortion. During calibration and operation, these pre-computed factors are applied to correct images before further processing, thereby reducing re-projection errors while maintaining calibration simplicity.
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 improves navigation accuracy and reduces camera calibration re-projection errors, providing more reliable and precise image correction for medical navigation systems, even in dynamic environments.
Implementation Method 1
The image is produced by converting the x-ray photons into light photons at the image intensifier input phosphor, converting the visible light photons into electrons at the photocathode
Implementation Method 2
accelerating and focusing the electrons through use of electrodes, and finally, converting the electrons back into visible light at the output phosphor
Implementation Method 3
S-distortion associated with the IIDs is at least partially caused by the magnetic field effect of the earth on the paths of the moving electrons within the IID. Electrons within the IID move in paths along designated lines of flux. External electromagnetic sources, such as the earth's magnetic field, affect electron paths at the perimeter of the image intensifier more so than those nearer the center.
Data Source
AI summary
Certain embodiments of the present invention provide for a system and method for modeling S-distortion in an image intensifier. In an embodiment, the method may include identifying a reference coordinate on an input screen of the image intensifier. The method also includes computing a set of charged particle velocity vectors. The method also includes computing a set of magnetic field vectors. The method also includes computing the force exerted on the charged particle in an image intensifier. Certain embodiments of the present invention include an iterative method for calibrating an image acquisition system with an analytic S-distortion model. In an embodiment, the method may include comparing the difference between the measured fiducial shadow positions and the model fiducial positions with a threshold value. If the difference is less than the threshold value, the optical distortion parameters are used for linearizing the set of acquired images.