Bone Rotation Center Determination via Epipolar Geometry
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Solution Overview
Problem
Current methods for determining the center of rotation of a bone, especially in medical applications like joint replacement, are inadequate as they rely on marker devices attached to the bone, which may not accurately represent the bone's movement due to camera displacement and lack precision in calculating the center of rotation from image data.
Innovation Solution
A computer-implemented method that acquires image data of a marker device attached to a bone as it rotates, forms image pairs, calculates transformations of the marker device, and compensates for camera displacement to determine the center of rotation relative to the marker device, using techniques such as epipolar geometry and essential matrix calculations to achieve accurate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a marker device is attached to the bone for tracking movement, then the bone's position and orientation can be monitored, but the marker device may not accurately represent the bone's movement due to potential displacement between the marker and the bone
Solution Approach 1:
The patent replaces direct mechanical attachment of markers to bones with an optical/image-based tracking system. Instead of relying on physical markers that may displace from the bone, the system uses successive images to track bone movement and calculate the center of rotation mathematically, eliminating the reliability issue of marker-bone displacement.
Solution Approach 2:
The patent introduces an intermediary computational process between the observed marker movement and the determined bone rotation. By calculating transformations from successive images and using these to determine the center of rotation, the system creates a mathematical intermediary that accounts for any marker displacement, ensuring accurate bone movement tracking.
2Measurement precision
If successive images are acquired to track bone rotation, then the center of rotation can be determined, but camera displacement between images introduces errors in the measurement
Solution Approach 1:
The patent extracts and separates the camera displacement component from the overall image transformation. By identifying and removing the camera movement effect from the successive images, the system isolates the pure bone rotation information, allowing accurate center of rotation determination without contamination from camera motion.
Solution Approach 2:
The patent performs additional computational steps beyond simple marker tracking, including calculating transformations from successive images and compensating for camera displacement. This excessive computational action ensures that even if camera movement occurs, the final center of rotation determination remains accurate by accounting for these partial effects.
3Device complexity
If a single marker is used to track bone movement, then the system is simple to implement, but the precision in determining the center of rotation is insufficient
Solution Approach 1:
The patent transitions from tracking only the position of a single marker to analyzing the transformation of the entire marker device across multiple dimensions. By examining successive images and calculating transformations in three-dimensional space, the system determines the center of rotation with higher precision while maintaining relative system simplicity.
Data Source
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AI summary
A computer implemented method for determining a center of rotation of a bone, comprising the steps of: a) acquiring image data representing a plurality of images taken by a camera while the bone is being rotated about the center of rotation, wherein the images show a marker device attached to the bone; b) forming a plurality of image pairs from the image data, wherein each image pair comprises two different images; c) determining a first relative position of the marker device relative to the camera from a first image of an image pair; d) determining a second relative position of the marker device relative to the camera from a second image of the same image pair; e) calculating a transformation of the first relative position into the second relative position; f) repeating steps c) to e) for all image pairs to obtain a plurality of transformations; and calculating the location of the center of rotation of the bone relative to the marker device from the plurality of transformations.