Time-Separated X-Ray Image Registration Using Rigid-Element Homographies
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Solution Overview
Problem
Existing imaging technologies struggle to accurately register and quantify changes in patient anatomy over time, particularly after medical implant placement, due to variations in camera pose, patient position, noise in image labels, and non-rigid transformations of the spine, making it difficult to compare images taken weeks, months, or years apart.
Innovation Solution
The method involves identifying corresponding points on rigid elements in two images, calculating homography transformations, clustering these transformations to account for camera and anatomical changes, and filtering out noise to accurately register and quantify changes in patient anatomy, using a system with a processor and memory to execute algorithms for image processing and registration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If images are registered over long time periods, then the ability to track anatomical changes is improved, but accuracy deteriorates due to camera pose variations and non-rigid transformations
Solution Approach 1:
The patent segments the anatomical structure into multiple rigid elements (vertebrae) that can be individually tracked. By dividing the spine into discrete rigid segments, the system can compute transformations for each element separately, thereby handling non-rigid transformations of the overall structure while maintaining registration accuracy for individual rigid components over long time periods.
Solution Approach 2:
The patent introduces an intermediary computational process that separates camera pose transformations from anatomical pose transformations. By computing homographies for each rigid element and then decomposing these transformations, the system acts as an intermediary that filters out camera-related variations while preserving true anatomical changes, thus maintaining accuracy over long time periods.
2Reliability
If transformations are calculated for each rigid element, then the ability to account for individual element changes is improved, but computational complexity increases
Solution Approach 1:
The patent divides the anatomical structure into multiple rigid elements and calculates homography transformations for each segment independently. This segmentation approach improves reliability by accounting for individual element movements while the modular nature of processing each element separately keeps computational complexity manageable through systematic organization.
Solution Approach 2:
The patent merges the individual transformations from multiple rigid elements into a unified registration process. By combining the homographies from segmented elements and separating common camera pose effects from individual anatomical changes, the system achieves high reliability through comprehensive tracking while maintaining computational efficiency through consolidation of results.
3Measurement precision
If clustering is used to separate camera pose changes from anatomical changes, then registration accuracy is improved, but processing time increases
Solution Approach 1:
The patent performs preliminary computation of homography transformations for each rigid element before the clustering separation step. By pre-calculating these transformations and organizing them by rigid element, the system prepares the data in advance for the clustering process, thereby improving registration precision through thorough analysis while reducing processing time by avoiding redundant calculations during the separation phase.
Data Source
AI summary
A method according to one embodiment of the present disclosure comprises receiving a first image of a patient's anatomy, the first image generated at a first time and depicting a plurality of rigid elements; receiving a second image of the patient's anatomy, the second image generated at a second time after the first time and depicting the plurality of rigid elements; determining a transformation from the first image to the second image for each one of the plurality of rigid elements to yield a set of transformations; calculating a homography for each transformation in the set of transformations to yield a set of homographies; and identifying, using the set of homographies, a common portion of each transformation attributable to a change in camera pose, and an individual portion of each transformation attributable to a change in rigid element pose.