High Permeability Waveguide Enclosure for MRI Linac Shielding
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Solution Overview
Problem
In Magnetic Resonance (MR) guided linear accelerator systems, the strong magnetic fields from the MRI system cause beam deflection of the linear accelerator, and the high voltages used in the accelerators introduce signal noise into the MR imaging system, degrading imaging quality.
Innovation Solution
A waveguide enclosure made of high magnetic permeability material is mounted around the linear accelerator, providing a continuous shield against static magnetic fields and reducing the impact of accelerating electrons' magnetic fields on the MR system, with strategically designed apertures and a collar to minimize electromagnetic leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the linear accelerator is mounted within the MRI system, then real-time image guidance and tumour targeting accuracy are improved, but beam deflection occurs due to strong magnetic fields
Solution Approach 1:
The waveguide is divided into multiple sections, each surrounded by its own magnetic shielding enclosure. This segmentation allows the magnetic field to be contained locally around each accelerator section, preventing beam deflection while maintaining the integrated MRI/linac system configuration for real-time imaging guidance.
Solution Approach 2:
A magnetic shielding enclosure made of high permeability material is introduced as an intermediary between the linear accelerator waveguide and the MRI environment. This enclosure acts as a mediator that allows the accelerator to operate within the MRI system while blocking the harmful magnetic field interactions that would cause beam deflection.
2Power
If high voltages are used in the linear accelerator, then radiation production efficiency is improved, but signal noise is introduced into the MR imaging system
Solution Approach 1:
The magnetic shielding enclosure serves as an intermediary that also electrically isolates the high voltage components of the linear accelerator from the MRI system. This dual-function shielding blocks both magnetic field interference (preventing beam deflection) and electrical noise transmission (preserving MR image quality), allowing high power operation without degrading imaging signals.
3Object-affected harmful factors
If the waveguide enclosure is made continuous around the accelerator, then magnetic field shielding effectiveness is improved, but manufacturing complexity increases
Solution Approach 1:
The continuous magnetic shielding enclosure is segmented into multiple modular sections that can be manufactured separately and then assembled around the waveguide. This segmentation maintains the shielding effectiveness by ensuring continuous coverage, while simultaneously reducing manufacturing complexity by allowing each section to be produced using standard fabrication processes and then joined together.
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
The solution effectively shields the linear accelerator from MRI magnetic fields, preventing beam deflection and reducing signal noise, thereby enhancing MR imaging quality and maintaining accurate radiation delivery.
Implementation Method 1
A waveguide enclosure made of high magnetic permeability material is mounted around the linear accelerator, providing a continuous shield against static magnetic fields
Implementation Method 2
with strategically designed apertures and a collar to minimize electromagnetic leakage
Data Source
AI summary
A radiotherapy apparatus adapted for use with a Magnetic Resonance Imaging (MRI) system, the radiotherapy apparatus comprising a linear accelerator, the linear accelerator including an electron source. In the linear accelerator electrons which are introduced by the source are accelerated to impact on a target and produce a beam of radiotherapeutic radiation. The linear accelerator has an accelerator waveguide within which the electrons are accelerated and an external waveguide enclosure; this enclosure extends substantially continuously over the accelerator waveguide. The waveguide enclosure is formed of a high magnetic permeability material and has a first aperture for the beam of radiotherapeutic radiation where the beam exits the waveguide enclosure and enters the MRI system and a second aperture for an RF guide for the introduction of electrons into the accelerator waveguide and for electrical lines for the particle source and coolant lines for the waveguide to pass through the enclosure and no other openings. The waveguide enclosure is preferably fabricated in a plurality of discrete parts.