RF Coil Array for Linac-MR Imaging
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Solution Overview
Problem
In combined linear accelerator and magnetic resonance imaging systems (Linac-MR), traditional RF coil arrays can increase the surface dose due to interactions with treatment beams, leading to harmful skin reactions, and require design considerations for maintaining consistent image quality during gantry rotation in parallel Linac-MR systems with rotating main magnetic fields.
Innovation Solution
A novel RF coil array comprising three electrically isolated coils, concentrically overlaid to form a stack, with a single turn coil and pair of butterfly or figure-eight coils, configured to sense magnetization precession in three orthogonal planes, ensuring zero mutual inductance and maintaining consistent image quality across 360 degrees of gantry rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional RF coil arrays are used in Linac-MR systems, then imaging capability is provided, but surface dose increases leading to harmful skin reactions
Solution Approach 1:
The RF coil array is divided into multiple individual coil elements that are electrically isolated from each other. Each coil element can be independently controlled and tuned, allowing selective activation and optimization of specific coils based on the treatment field position, thereby reducing unnecessary RF exposure to the patient's skin while maintaining imaging capability.
Solution Approach 2:
The RF coil array incorporates dynamic tuning capabilities where each coil element can be independently adjusted in real-time during the imaging and treatment process. This allows the system to adapt the RF coil configuration to match the moving treatment field, ensuring that active coils are only those necessary for current imaging needs, thus minimizing surface dose accumulation.
2Object-affected harmful factors
If RF coil array is positioned to avoid treatment beam collisions, then surface dose is reduced, but image quality may deteriorate
Solution Approach 1:
The RF coil array is designed with multi-functional coil elements that can serve different imaging purposes (e.g., surface coils, volume coils, phased array elements) within a single integrated structure. This allows the system to maintain high image quality across various imaging scenarios while keeping the overall coil configuration optimized to minimize interference with treatment beams.
Solution Approach 2:
The system dynamically adjusts various parameters of the RF coil array including coil activation patterns, tuning frequencies, and signal processing weights to optimize image quality for different imaging planes and depths. These parameter changes are made in real-time to maintain diagnostic image quality while keeping the physical coil positions fixed in a beam-avoiding configuration.
3Measurement precision
If multiple coils are stacked concentrically to sense magnetization in three orthogonal planes, then imaging coverage is improved, but mutual inductance between coils increases
Solution Approach 1:
The concentrically stacked coils are designed with asymmetric geometries and orientations that break the symmetry of magnetic coupling between adjacent coils. By using non-uniform coil shapes, different winding patterns, and strategic positioning, the design minimizes mutual inductance while maintaining the ability to sense magnetization in three orthogonal planes through careful geometric arrangement.
Solution Approach 2:
Electrical isolation structures and magnetic shielding materials are introduced as intermediaries between adjacent stacked coils. These elements act as barriers that reduce magnetic coupling and mutual inductance between coils while allowing each coil to independently sense magnetization signals from the patient's body in its respective orientation.
4Stability of the object's composition
If RF coil array is designed for parallel Linac-MR with rotating gantry, then consistent imaging during rotation is achieved, but design complexity increases
Solution Approach 1:
Multiple RF coil elements with different sensitivity profiles and orientations are merged into a single integrated array that collectively provides consistent imaging coverage throughout the full 360-degree gantry rotation. The combined signal from all coils, processed through sophisticated signal combining algorithms, maintains stable image quality regardless of gantry position, eliminating the need for mechanically reconfiguring coils during rotation.
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 RF coil array effectively eliminates mutual inductance and maintains consistent signal-to-noise ratio (SNR) across gantry angles, reducing surface dose and ensuring high-quality imaging during radiation therapy, while avoiding collisions with treatment beams.
Implementation Method 1
MRI signals are radiated by excited nuclei in the target tissue in the intervals between consecutive RF pulses as a result of the deflected magnetization vector returning to the resting state. The sensed MRI signals are in turn digitized and processed
Implementation Method 2
the coils being configured such that adjacent coils in the stack have substantially zero mutual inductance
Data Source
AI summary
A radio frequency (RF) coil array for use with a magnetic resonance system having a rotating main magnetic field B0 comprises at least three separate coils, the coils being electrically isolated from one another, concentrically overlaid to form a stack, and configured to sense magnetization precession in three orthogonal planes.