MRI Apparatus with Maxwell-like Coils for Radiotherapy Integration
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Solution Overview
Problem
Integrating magnetic resonance imaging (MRI) with radiotherapy is challenging due to the interference of MRI magnetic fields with electron linear accelerators, causing functionality issues and dose distribution perturbations, and existing solutions often require complex shielding or large MRI designs that are not practical for clinical settings.
Innovation Solution
The use of a parallel coil configuration with Maxwell-like coils and focusing magnets to generate a homogeneous magnetic field parallel to the electron motion, allowing the linear accelerator to operate within the MRI field without shielding, while also reversing magnetic fields to defocus scattered electrons and reduce surface dose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional MRI magnet configuration is used to provide a homogeneous magnetic field for imaging, then imaging quality is improved, but the magnetic field interferes with electron linear accelerator operation and distorts dose distribution
Solution Approach 1:
The patent applies local quality by creating different magnetic field characteristics in different spatial zones: a homogeneous magnetic field in the imaging zone for MRI quality, and a magnetic field-free or shielded zone in the linear accelerator path to prevent electron beam interference and dose distribution distortion. This allows each functional zone to have the magnetic field properties it needs without compromising the other.
2Reliability
If magnetic shielding is introduced to protect the linear accelerator from magnetic field interference, then linear accelerator functionality is improved, but the MRI magnet design complexity increases
Solution Approach 1:
The patent segments the magnetic field environment into distinct regions using magnetic shielding structures that partition the space between the MRI magnet and linear accelerator. This segmentation allows the homogeneous magnetic field to be maintained in the imaging zone while creating protected zones for the linear accelerator, reducing the need for complex overall magnet redesign.
3Ease of operation
If the MRI magnet is designed to provide direct access to the patient, then ease of operation is improved, but the magnetic field still interferes with linear accelerator electron motion
Solution Approach 1:
The patent introduces magnetic shielding structures as intermediary elements between the MRI magnet and the linear accelerator electron beam path. These shields act as mediators that block or redirect magnetic field lines, protecting the electron motion from magnetic field interference while maintaining open patient access for both imaging and treatment.
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 configuration maintains the functionality of the linear accelerator within the MRI field, reduces dose distribution perturbations, and minimizes surface dose by focusing electrons, creating a clinically usable radiation beam.
Implementation Method 1
the coil pairs being configured to generate a substantially homogenous magnetic field in a first transverse direction in the common transverse plane, in the imaging area between the two sets of coil pairs
Implementation Method 2
at least one focusing magnet positioned in the peripheral areas, substantially parallel to the first transverse direction, the at least one focusing magnet being configured to generate a focusing magnetic field in a focusing area, in a direction substantially the same as the first transverse direction
Implementation Method 3
The radiotherapy dose distribution in the patient is affected by the magnetic field in the patient since the electrons scattered by the incident photons are also affected by the magnetic field of the MRI by the Lorentz force F=ev×B
Data Source
AI summary
A magnetic resonance imaging (MRI) apparatus suitable for radiotherapy. The apparatus includes two sets of coil pairs, each coil pair forming a Maxwell-like coil. The two sets of coil pairs share a common transverse plane, have opposing polarities, and define a common plane of symmetry and an imaging area. The two sets generate a substantially homogenous electromagnetic field in a first transverse direction in the imaging area and peripheral electromagnetic fields in a direction opposite to the first transverse direction in a peripheral area. The apparatus also includes at least one focusing magnet positioned in the peripheral areas to generate a focusing electromagnetic field in a focusing area, in a direction substantially the same as the first transverse direction. At least a portion of the peripheral electromagnetic fields is maintained in a defocusing area between the focusing area and the imaging area.