Double Layer RF Coil Array for SAR Reduction in High Field MRI
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Solution Overview
Problem
High and ultra-high field magnetic resonance imaging (MRI) systems face challenges with inhomogeneous RF radiation effects and high specific energy absorption rate (SAR) when using large body coils, which are not well-suited for cardiac and abdominal imaging, limiting signal-to-noise ratio (SNR) and patient comfort.
Innovation Solution
A double-layer transmit and receive (T/R) coil array is designed with a radio frequency (RF) shield, a transmit coil strip positioned close to the shield, and a receive coil strip further away, optimized for low SAR and high SNR, using capacitive coupling and decoupling techniques to manage RF currents and reduce radiation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large body coil is used for high field MRI, then coverage is improved, but SAR increases and B1 homogeneity deteriorates
Solution Approach 1:
The patent divides the single large body coil into multiple separate coil elements arranged in an array. Each coil element is independently controlled, allowing selective activation to cover the entire body while reducing SAR through parallel imaging techniques and optimized current distribution across the segmented elements.
Solution Approach 2:
The patent implements local control of each coil element with independent amplitude and phase adjustment. This allows optimization of B1 field distribution and SAR in different regions of the body, enabling tailored RF pulse sequences that adapt to local tissue properties and imaging requirements.
2Area of stationary object
If a large body coil is used for high field MRI, then coverage is improved, but B1 homogeneity deteriorates
Solution Approach 1:
The patent segments the coil system into multiple independently controllable elements, enabling separate optimization of B1 field distribution across different regions. This segmentation allows compensation for dielectric resonance and eddy current effects that cause B1 inhomogeneity in large body coils.
Solution Approach 2:
The patent employs dynamic adjustment of amplitude and phase parameters for each coil element based on measured or simulated B1 field distributions. This parameter optimization compensates for frequency-dependent B1 inhomogeneity and dielectric effects, achieving uniform excitation across the entire field of view at high field strengths.
3Object-affected harmful factors
If conventional surface coils are used, then SAR is reduced, but SNR and imaging quality deteriorate
Solution Approach 1:
The patent merges the advantages of surface coils (low SAR) with those of body coils (high SNR) by combining multiple surface coil elements into a coordinated array. The merged system maintains low SAR through localized excitation while achieving high SNR through constructive interference and optimized signal reception across multiple elements.
Solution Approach 2:
The patent designs coil elements that serve multiple functions: they act as both transmit and receive elements, and can be selectively activated for different imaging applications. This multi-functionality allows the system to optimize for both low SAR and high SNR by adapting the active coil configuration to specific imaging requirements.
4Object-affected harmful factors
If local T/R arrays are used, then SAR is reduced, but device complexity increases
Solution Approach 1:
The patent segments the coil array into modular elements that can be independently controlled, allowing systematic management of complexity through standardized units. Each segment follows the same basic design and control architecture, simplifying the overall system while enabling sophisticated SAR and B1 optimization.
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 reduces SAR during transmission, increases SNR during reception, improves TEM transmit parallel imaging, provides more patient space, and facilitates ultra-short transmit pulse durations, enhancing imaging quality and safety at high field strengths.
Implementation Method 1
using capacitive coupling and decoupling techniques to manage RF currents and reduce radiation effects
Implementation Method 2
Radio frequency (RF) radiation effects are increasing with frequency and inner bore diameter
Implementation Method 3
receiving magnetic resonance signals with the receive coil strip
Data Source
AI summary
A high or ultra-high field magnetic resonance imaging method and device including a double-layered transmit-receive coil array that includes a transmit element placed in close proximity to a radio frequency shield to reduce SAR, and a receive element that is placed further away from the shield to improve SNR. The transit and receive elements may be mutually decoupled using diodes, transformers, or other decoupling techniques. A portion of the transmit element may pass in front of the RF shield while capacitors in the transmit element may be positioned behind the shield.