Magnetic Correcting Element for MRI Radiotherapy Field Homogeneity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic field perturbations caused by ferromagnetic materials in radiation therapy systems during MRI-guided radiotherapy are not effectively compensated, leading to image artifacts and distortion, especially when the radiation source rotates around the MRI magnet, as existing methods are inadequate for time-dependent perturbations.
Innovation Solution
The method involves using either passive compensation elements, such as ferromagnetic bodies with opposite magnetization, or active compensation coils to correct the magnetic field, positioned strategically relative to the ferromagnetic components to minimize field changes, and adjusting their positions or current supply to maintain field homogeneity independently of the gantry's position and velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ferromagnetic materials are used in the radiation therapy gantry, then the radiation therapy function is enabled, but magnetic field perturbations occur causing image artifacts and distortion
Solution Approach 1:
The patent applies magnetic compensation elements that generate opposing magnetic fields to counteract the perturbations caused by ferromagnetic materials in the gantry. The compensation elements are strategically positioned and magnetized to create fields that cancel out the harmful effects, converting the magnetic interference problem into a solvable field cancellation task.
Solution Approach 2:
The patent introduces magnetic compensation elements as intermediary components between the ferromagnetic gantry materials and the MRI imaging zone. These compensation elements act as mediators that interact with both the disturbing magnetic fields and the imaging region, reducing the net perturbation without requiring removal of the essential ferromagnetic components.
2Productivity
If the gantry rotates around the MRI magnet, then radiation therapy delivery is enabled, but time-dependent magnetic field perturbations occur
Solution Approach 1:
The patent positions magnetic compensation elements in advance on the gantry structure, before rotation begins. These elements are pre-configured with specific magnetizations and positions calculated to counteract the expected time-dependent perturbations throughout the rotation cycle, enabling continuous compensation without real-time adjustment.
Solution Approach 2:
The compensation elements are designed to provide continuous magnetic field compensation throughout the entire gantry rotation. The strategic positioning and magnetization of these elements ensure that the compensatory effect persists continuously as the gantry rotates, maintaining field homogeneity without interruption or need for repositioning.
3Measurement precision
If existing compensation methods are used, then some magnetic field correction is achieved, but compensation is not independent of gantry position and velocity
Solution Approach 1:
The patent employs asymmetric positioning of magnetic compensation elements relative to the gantry rotation axis and imaging zone. By strategically placing elements at specific asymmetric locations and configuring their magnetizations accordingly, the system achieves position-independent compensation where the net effect remains constant regardless of gantry orientation.
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 significantly reduces magnetic field variations within the imaging zone, ensuring high-quality MRI images and precise radiation dose delivery by maintaining a homogeneous magnetic field even under non-static conditions, with residual field perturbations minimized below 50nT.
Implementation Method 1
a magnetic correcting element located on a radial path perpendicular to the rotational axis... The magnetic correcting element is to be rotated by the gantry... such that the change in the magnetic field within the imaging zone due to the rotation of the ferromagnetic component is reduced
Implementation Method 2
the radiation source rotating around the MR magnet on a gantry contains ferromagnetic materials which can disturb the magnetic field within the imaging volume
Implementation Method 3
A static magnetic field is used by Magnetic Resonance Imaging (MRI) scanners to align the nuclear spins of atoms
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method of correcting a magnetic field of an MRI radiotherapy apparatus (300) comprising a magnetic resonance imaging system (302) and a radiation therapy system (304). The MRI system includes a magnet (306) for generating the magnetic field within an imaging zone 318. The magnet generates a magnetic field with a zero crossing (346, 404) outside of the imaging zone. The medical apparatus further comprises a gantry (332) configured for rotating a ferromagnetic component (336, 510) about a rotational axis (333). The method comprises the step of installing (100, 200) a magnetic correcting element (348, 900, 1000) located on a radial path (344, 504) perpendicular to the rotational axis. The magnetic correcting element is positioned on the radial path such that change in the magnetic field within the imaging zone due to the ferromagnetic component is reduced. The method further comprises repeatedly: measuring (102, 202, 1204) the magnetic field within the imaging zone; determining (104, 204, 1206) the change in the magnetic field in the imaging zone; and adjusting (106, 206, 1208) the position of the magnetic correcting element along the radial path if the change in the magnetic field is above a predetermined threshold.