Fiducial-Free CBCT Tracking via Probe Trace Registration
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Solution Overview
Problem
Current image-guided surgical implant systems rely on fiducials for accurate tracking, which can lead to inaccuracies due to discrepancies in fixture placement, limited space in the oral cavity, and workflow burdens, especially when CBCT scans are not available at the time of surgery.
Innovation Solution
A method that determines the relationship between pre-operative CBCT and real-time surgical environments without fiducials, using a 3D model of the rigid body, a probe with a tracking reference component, and a rigidly affixed tracking reference component to track locations and determine a transform that relates the probe locations to the 3D model, allowing for immediate fixture placement and correction of imprecise fixture placement during surgery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiducials are used for tracking reference, then tracking accuracy is improved, but placement discrepancies between CBCT scan and surgery reduce reliability
Solution Approach 1:
The system performs probe tracing to capture the spatial relationship between the fixture and patient anatomy immediately before surgery, creating a pre-operative map that can be used for registration even if the fixture is repositioned during surgery. This preliminary capture of spatial data resolves the contradiction by decoupling the timing of reference establishment from the timing of surgery.
Solution Approach 2:
The system uses real-time optical tracking of the fixture and probe, combined with feedback from the probe trace comparison against the pre-operative CBCT, to continuously refine and correct the registration transform during surgery. This feedback loop compensates for placement discrepancies and maintains both tracking accuracy and guidance reliability.
2Ease of operation
If a fixture is used for tracking, then real-time surgical tracking is enabled, but limited oral cavity space constrains fixture size and increases placement inaccuracy
Solution Approach 1:
The system introduces a probe as an intermediary tool that traces the patient's anatomy to establish the registration transform, rather than relying solely on the fixture's position. This intermediary probing process compensates for the fixture's limited size and placement inaccuracies, maintaining tracking capability while reducing the impact of fixture constraints.
Solution Approach 2:
The registration process is segmented into multiple independent components: fixture tracking, probe tracing, and transform calculation. This segmentation allows each component to be optimized independently - the fixture can be small for ease of placement, while the probe tracing provides additional reference data to maintain overall registration accuracy.
3Measurement precision
If fiducials are required in pre-operative CBCT, then accurate registration is possible, but workflow complexity increases due to fixture management and coordination
Solution Approach 1:
The system makes the fixture serve multiple functions: it provides both the pre-operative reference frame for CBCT registration and the real-time tracking reference during surgery. This multi-functionality eliminates the need for separate fiducial management and reduces coordination complexity between CBCT acquisition and surgical procedures.
Solution Approach 2:
The system performs the probe tracing and registration calculation in advance, creating a transform that can be applied even if the CBCT was acquired at a different time or by a different provider. This preliminary registration work reduces the coordination burden and allows flexibility in when and where the CBCT is obtained.
4Ease of manufacture
If fixture placement is performed prior to CBCT acquisition, then fiducial-based registration is possible, but inaccuracies arise from displacement between scan and surgery
Solution Approach 1:
The system captures the fixture's position and the patient's anatomy through probe tracing immediately before surgery, creating a preliminary reference state. This preliminary action allows the system to calculate a registration transform that accounts for any displacement that occurs between the pre-operative CBCT and the actual surgery, maintaining accuracy despite temporal separation.
Solution Approach 2:
The system uses feedback from comparing the probe trace against the CBCT-derived 3D model to continuously refine the registration transform. This feedback mechanism compensates for any displacement or deformation that occurs between fixture placement, CBCT acquisition, and surgery, maintaining measurement precision throughout the workflow.
Data Source
AI summary
A method for referencing a tracking system's coordinate frame to a rigid body's coordinate frame is disclosed. The method involves obtaining a 3D model depicting some of the surfaces of the rigid body. A probe is provided with an affixed tracking reference component. A second tracking reference component is attached to the rigid body. The method involves tracking locations of the probe as it moves along surfaces of the rigid body and then determining a transform that relates the probe locations to the 3D model of the rigid body. In one embodiment the rigid body is a dental mandible or maxilla of a patient and the 3D model is a surface extracted from a computed tomography image of the patient's jaw and teeth.