Birdcage Coil Segmentation for MRI X-Ray Beam Attenuation
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Solution Overview
Problem
Current whole body coils (WBCs) in MRI systems face challenges in achieving good B1 field uniformity while allowing large enough openings for radiation or X-ray beams to pass through with minimal beam attenuation, as reducing the number of conductive rungs compromises B1 field uniformity.
Innovation Solution
The design incorporates a birdcage coil with a plurality of rung groups and windows, where each rung group comprises multiple conductive rungs connected between two conductive rings, with windows providing larger beam-through areas, maintaining B1 field uniformity comparable to traditional WBCs with fewer rungs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of conductive rungs is increased to improve B1 field uniformity, then B1 field uniformity is improved, but the beam-through area is reduced and beam attenuation increases
Solution Approach 1:
The patent divides the conductive rungs into multiple groups (first rung group, second rung group, etc.) that are azimuthally separated by windows. Each group contains multiple conductive rungs that are azimuthally spaced apart, allowing the system to maintain B1 field uniformity through coordinated operation of multiple groups while preserving beam-through areas through the windows.
Solution Approach 2:
The patent creates different functional zones within the birdcage coil structure. The conductive rungs in each group provide magnetic field generation in specific azimuthal regions, while the windows in between provide radiation transmission paths. This local differentiation allows simultaneous optimization of B1 field uniformity in the coil regions and beam-through area in the window regions.
2Area of stationary object
If the number of conductive rungs is reduced to increase beam-through area, then beam-through area is improved, but B1 field uniformity deteriorates
Solution Approach 1:
Instead of using a single set of conductive rungs, the patent segments the coil into multiple azimuthally separated rung groups. Each group contains multiple conductive rungs that work together to maintain B1 field uniformity, while the windows between groups provide beam-through areas. This segmentation allows the system to achieve both goals simultaneously.
Solution Approach 2:
The birdcage coil structure is designed to perform multiple functions simultaneously: the conductive rungs generate B1 magnetic fields for MRI imaging, while the windows allow radiation beams to pass through for radiation therapy applications. This multi-functionality resolves the contradiction by making the same structure serve dual purposes without requiring separate components.
3Reliability
If a thick copper sheet is used as RF shield to provide good decoupling, then decoupling performance is improved, but eddy currents increase during strong gradient pulses
Solution Approach 1:
The patent uses a copper sheet with many slots cut into it, creating a porous or slotted structure. This modified copper sheet maintains the RF shielding and decoupling properties of a solid copper sheet while the slots reduce the continuous conductive paths, thereby minimizing eddy currents during strong gradient pulses. The slotted structure allows electromagnetic fields to pass through more effectively while maintaining mechanical integrity and RF blocking capabilities.
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 allows for small and uniform beam attenuation, enabling the use of MRI in new medical modalities while maintaining B1 field uniformity, effectively increasing the number of applications that can utilize MRI systems.
Implementation Method 1
A birdcage coil comprises two conductive rings with a plurality of conductive rungs extending between the two conductive rings... The B1 field uniformity from a birdcage coil in the Field-of-View (FOV) is important (e.g., to generate high quality images)
Implementation Method 2
The RF shield is configured to provide two functions. The first function is to provide decoupling between the WBC and the gradient coils
Implementation Method 3
An MRI scanner has a set of gradient coils (e.g., x, y, and z gradient coils). These gradient coils are typically located outside of the WBC. Gradient coils are typically made of copper wires and couple to the WBC
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a magnetic resonance imaging (MRI) radio frequency (RF) coil. The MRI RF coil comprises a first conductive ring and a second conductive ring. A plurality of rung groups extend between the first and second conductive rings. The plurality of rung groups are spaced uniformly about the first conductive ring. Each of the plurality of rung groups comprises a plurality of conductive rungs extending between and connected to the first and second conductive rings. The plurality of conductive rungs of each of the plurality of rung groups are azimuthally separated from one another by a first azimuth angle. Each of the plurality of rung groups is separated from a neighboring rung group by a spacing that forms a window. Each of the windows have a second azimuth angle that is greater than the first azimuth angle.