Stereoscopic Camera Calibration via Phantom-Based Iso-Centre Alignment
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Solution Overview
Problem
Existing methods for calibrating stereoscopic camera systems for radiotherapy treatment apparatuses are not sufficiently accurate, leading to uncertainties in patient positioning and dosimetric accuracy, and rely on potentially error-introducing laser systems for iso-centre verification.
Innovation Solution
A method involving the use of a calibration phantom positioned at an estimated iso-centre, irradiated and imaged to determine its relative location, with subsequent repositioning and imaging to set the stereoscopic camera system's coordinate system directly based on the phantom's location, eliminating the need for laser-based iso-centre verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser-based iso-centre verification is used, then the calibration process can be performed, but errors are introduced and repeated calibration checks are required
Solution Approach 1:
The patent removes the laser system from the calibration process entirely. Instead of using laser-based iso-centre verification, the invention uses a calibration phantom with known geometry that is imaged by the stereoscopic camera system and compared with CAD models, extracting the calibration function from the problematic laser verification step.
Solution Approach 2:
The calibration phantom serves as an intermediary object between the camera system and the iso-centre. The phantom's known geometric features mediate the calibration process, allowing the camera system to determine its coordinate system relative to the iso-centre without requiring laser verification.
2Measurement precision
If conventional calibration methods are used, then the process can be completed, but calibration accuracy is insufficient leading to positioning uncertainties
Solution Approach 1:
The calibration phantom is positioned at the estimated iso-centre location before the actual calibration imaging. The coordinate system transformation is pre-calculated based on the phantom's known geometry and the camera's observed perspective, allowing for accurate patient positioning without time-consuming iterative adjustments.
Solution Approach 2:
The calibration phantom creates a known geometric copy or reference frame at the iso-centre location. By comparing the phantom's actual image with its CAD model, the system establishes an accurate coordinate transformation without requiring physical measurement tools or time-consuming manual calibration procedures.
3Measurement precision
If extensive quality assurance programs are implemented, then dosimetric accuracy can be improved, but system complexity increases
Solution Approach 1:
The calibration phantom is self-contained with known geometric features that automatically provide calibration information. The system performs self-calibration by comparing the phantom's observed features with its CAD model, eliminating the need for complex external quality assurance equipment or procedures.
Solution Approach 2:
The calibration phantom serves multiple functions: it provides coordinate system calibration, verifies camera positioning accuracy, and establishes the relationship between the camera coordinate system and the treatment iso-centre. This multi-functionality replaces multiple separate quality assurance procedures with a single integrated calibration process.
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 enhances calibration accuracy by directly linking the camera system's coordinate system to the treatment apparatus' iso-centre, reducing errors and eliminating the need for repeated laser calibration checks, thereby improving patient positioning and dosimetric accuracy.
Implementation Method 1
irradiated using the radio therapy treatment apparatus
Data Source
AI summary
The disclosed calibration method includes a calibration phantom positioned on an adjustable table on the surface of a mechanical couch, with the phantom's centre at an estimated location for the iso-centre of a radio therapy treatment apparatus. The calibration phantom is then irradiated using the apparatus, and the relative location of the center of the calibration phantom and the iso-centre of the apparatus is determined by analyzing images of the irradiation of the calibration phantom. The calibration phantom is then repositioned by the mechanical couch applying an offset corresponding to the determined relative location of the centre of the calibration phantom and the iso-centre of the apparatus to the calibration phantom. Images of the relocated calibration phantom are obtained, to which the offset has been applied, and the obtained images are processed to set the co-ordinate system of a stereoscopic camera system relative to the iso-centre of the apparatus.