Radiotherapy Phantom Alignment for MR Through-Plane Distortion
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Solution Overview
Problem
Radiotherapy treatments face challenges in accurately delivering radiation doses due to subject motion and image distortion caused by non-linear magnetic field gradients, leading to inconsistencies in contour display and image processing accuracy.
Innovation Solution
A method and phantom for evaluating contour display accuracy using a tapered phantom with a fixation mechanism, allowing alignment with different axes to assess through-plane distortion and compensate for image distortions, ensuring consistent and accurate image processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If MR imaging is used to obtain detailed anatomical information during radiotherapy treatment, then soft tissue contrast and anatomical visualization are improved, but through-plane distortion occurs due to non-linear magnetic field gradients
Solution Approach 1:
The patent uses a phantom with known geometric features (tapered cylinder with marked contours) to create a reference copy of the expected anatomical structure. By comparing the distorted MR image of the phantom against its known true geometry, the system can identify and quantify distortion patterns, then apply correction transformations to both the phantom images and patient images to restore geometric accuracy while preserving the soft tissue contrast benefits of MR imaging
Solution Approach 2:
The patent transforms the distorted MR images by applying geometric correction parameters derived from phantom analysis. The control device calculates distortion correction transformations that map the distorted image coordinates back to their true anatomical positions, effectively changing the spatial parameters of the images to eliminate through-plane distortion while maintaining the high soft tissue contrast characteristics of MR imaging
2Manufacturing precision
If image distortion correction is applied to compensate for non-linear magnetic field gradients, then geometric accuracy is improved, but contour display accuracy may be compromised without proper evaluation
Solution Approach 1:
The patent implements a feedback mechanism where the phantom images serve as a reference standard. The control device compares distorted and corrected images against the known true geometry of the phantom, evaluates the accuracy of distortion correction and contour display, and uses this feedback to optimize correction parameters. This closed-loop approach ensures that geometric accuracy improvements do not compromise contour display accuracy
Solution Approach 2:
The patent performs preliminary distortion evaluation and characterization using the phantom before treating actual patients. By acquiring and analyzing phantom images with known geometry, the system pre-determines distortion patterns and optimization parameters that will be applied to patient images, ensuring both geometric and contour accuracy are optimized before clinical use
3Measurement precision
If a phantom with fixed orientation is used for distortion evaluation, then measurement consistency is improved, but the ability to assess distortion in multiple anatomical planes is limited
Solution Approach 1:
The patent makes the phantom orientation dynamic by enabling rotation to multiple predetermined positions (e.g., 0°, 45°, 90°, 135°). The fixation mechanism allows the phantom to be securely positioned at each orientation, and the control device automatically adjusts evaluation parameters based on the current orientation. This dynamic approach maintains measurement consistency at each position while providing comprehensive multi-plane distortion assessment capability
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
Enhances the reliability and safety of radiotherapy by providing a robust evaluation of image distortion and correction, improving the accuracy of image processing and contour display.
Implementation Method 1
Localisation of measurement signals to different parts of the anatomy of the subject can be achieved by varying the magnetic field present at different spatial locations, (e.g., by introducing one or more magnetic field gradients)
Data Source
AI summary
A method for evaluating contour display accuracy for radiotherapy, a computer-readable medium and a phantom for use in evaluating contour display accuracy for radiotherapy are provided. The method includes obtaining, by a control device, a through-plane distorted MR image comprising a representation of a phantom disposed on a patient support surface of a radiotherapy device. The method further includes determining, by the control device, a difference between the representation of the phantom and a reference contour of the phantom.