ENT Image Registration Using Stable Bony Landmarks
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Solution Overview
Problem
In image-guided surgery, especially in ENT procedures, accurate registration between CT images and magnetic tracking systems is challenging due to the proximity of sinuses to critical organs, requiring methods to identify stable regions for precise alignment without movement, as external features like earlobes may shift when a magnetic sensor is positioned.
Innovation Solution
The method involves analyzing CT images to identify stable bony sections and using a magnetic tracking system to measure positions on the head, with a processor forming a correspondence between magnetic-system-positions and voxel subsets overlaying these bony sections to generate a registration, employing techniques like the iterative closest point (ICP) theorem to align the frames of reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If external features like earlobes are used for registration, then the registration process is simple, but the features may shift when a magnetic sensor is positioned causing inaccurate alignment
Solution Approach 1:
The patent applies local quality by selecting specific bony landmarks (such as the nasal bridge, orbital ridges, and mastoid processes) that have stable anatomical characteristics. These localized bony features are chosen because they provide consistent, non-movable registration points unlike soft tissue features, thereby resolving the contradiction between ease of operation and measurement precision.
2Reliability
If fluoroscopy is used for real-time tracking, then instrument positions can be presented on patient anatomy images, but ionizing radiation exposure increases
Solution Approach 1:
The patent uses magnetic field sensors as an intermediary tracking system that does not involve ionizing radiation. Magnetic sensors placed on or near the patient's head can track instrument positions in real-time without the harmful radiation effects of fluoroscopy, while still providing the necessary spatial information for image-guided surgery.
Solution Approach 2:
The patent replaces the mechanical fluoroscopy-based tracking system with an electromagnetic tracking system using magnetic fields. This substitution eliminates ionizing radiation exposure while maintaining real-time tracking capability, as magnetic sensors can continuously monitor instrument positions without harmful radiation.
3Measurement precision
If multiple registration points are acquired to improve accuracy, then the registration becomes more precise, but the time required for registration increases
Solution Approach 1:
The patent performs preliminary identification and selection of optimal bony landmarks from CT images before the actual registration process. By pre-selecting the best registration points based on their anatomical stability and accessibility, the system reduces the number of points that need to be physically acquired during surgery, thereby maintaining high accuracy while reducing registration time.
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 fast, efficient, and accurate registration of the magnetic tracking system's frame of reference with the CT imaging frame of reference, ensuring precise alignment even in sensitive areas like the sinuses, thereby enhancing surgical precision.
Implementation Method 1
a magnetic tracking system that is configured to measure positions on the patient's head
Data Source
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AI summary
A method, including receiving a computerized tomography (CT) image of voxels of a subject's head, and analyzing the image to identify respective locations of the subject's eyes in the image, so defining a first line segment joining the respective locations. The method includes identifying a voxel subset overlaying bony sections of the head, lying on a second line segment parallel to the first line segment and on a third line segment orthogonal to the first line segment. A magnetic tracking system configured to measure positions on the subject's head is activated, and a probe, operative in the system, is positioned in proximity to the bony sections to measure positions of a surface of the head overlaying the bony sections. A correspondence between the positions and the voxel subset is formed, and a registration between the CT image and the magnetic tracking system is generated in response to the correspondence.