MRI RF Antenna with Segmented Coaxial Shield
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Solution Overview
Problem
Conventional RF transmit antennas in MRI systems are ill-suited for body part-specific arrangements and can cause high Specific Absorption Rate (SAR) heating effects due to limitations in design and shape conformity, which affects imaging resolution and accuracy.
Innovation Solution
The development of an MRI system RF transmit antenna arrangement using a coaxial cable with breaks in the outer shield to create radiating elements, allowing for flexible shaping and reduced SAR levels by minimizing electric field generation, featuring a dipole or monopole antenna design with inductive components for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional RF transmit antennas are used in body part specific RF arrangements, then the antennas can be positioned close to the body part, but the antennas cannot conform to the shape of the body part and cause high SAR heating
Solution Approach 1:
The outer shield of the coaxial cable is divided into multiple discrete sections with gaps between them, transforming the continuous shield into segmented sections. This segmentation allows the antenna to conform to body part shapes while reducing continuous electric field generation and associated SAR heating effects
Solution Approach 2:
The shield sections are positioned at specific locations along the coaxial cable to create localized radiating elements. This allows different portions of the antenna to have different electrical characteristics, enabling shape conformity to body parts while controlling SAR through strategic placement of conductive sections
2Loss of energy
If the outer shield is made continuous to improve RF transmission, then the antenna structure is simpler, but SAR heating increases due to continuous electric field generation
Solution Approach 1:
The continuous outer shield is segmented into discrete sections with gaps. This maintains sufficient RF transmission efficiency through the conductive sections while breaking up continuous electric fields that cause SAR heating, achieving a balance between transmission efficiency and safety
Solution Approach 2:
The dielectric material filling the gaps between shield sections acts as an intermediary that maintains electrical isolation while allowing magnetic field penetration. This enables RF energy transmission through the gaps without creating continuous electric fields that would increase SAR
3Measurement precision
If local RF transmit antennas are added to body part specific RF arrangements, then imaging of selected locations is improved, but the complexity of the RF arrangement increases
Solution Approach 1:
The coaxial cable structure serves multiple functions: it provides RF transmission through the core, creates radiating elements through the shield sections, and allows shape conformity to body parts. This multi-functionality improves imaging precision without proportionally increasing system complexity
Solution Approach 2:
The transmit antenna function is merged with the existing coaxial cable structure used for RF transmission. By utilizing the outer shield as the radiating element, the patent combines transmission and radiation functions into a single component, reducing overall system complexity
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 antenna arrangement provides improved imaging resolution and reduced SAR heating, enabling more effective and flexible RF transmission while minimizing power loss and optimizing current distribution for enhanced MRI system performance.
Implementation Method 1
at least one of the shield portions acts as a radiating element when an RF source is connected to the feed point
Implementation Method 2
the heating effect is caused by electric fields which are generated in the subject as a by-product of creating the desired B1 field. In general it is desirable to minimise the SAR levels produced for any given strength of B1 field
Data Source
AI summary
An MRI system RF transmit antenna arrangement 3 including an antenna 5 including a length of coaxial cable 51 with an electrically conductive core 52 and an electrically conductive outer shield 53 through which the core runs, with the core having a feed point 52a arranged for electrical connection to an RF source and at least one break 53a being provided in the electrically conductive outer shield partway along the length of coaxial cable so as to divide the electrically conductive outer shield 53 into at least two axially spaced shield portions such that at least one of the shield portions acts as a radiating element when an RF source is connected to the feed point 52a.