Transmit Coil Screen Surfaces for MRI Decoupling
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Solution Overview
Problem
High-field magnetic resonance devices face image quality deterioration and specific absorption rate (SAR) issues due to interactions between conductor loops in transmit coil arrangements, leading to inadequate decoupling and increased costs with existing solutions.
Innovation Solution
A transmit coil arrangement with screen surfaces extending radially and longitudinally to decouple conductor loop groups, combined with capacitive decoupling and impedance elements, allows for effective decoupling and reduced SAR, enabling homogenization of magnetic fields and flip angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conductor loops are arranged densely to improve parallel transmission capability, then productivity increases, but coupling between adjacent loops increases causing image quality deterioration
Solution Approach 1:
A decoupling conductor is introduced as an intermediary element between adjacent conductor loops. This decoupling conductor carries a current that generates a magnetic field to cancel the coupling field between loops, enabling dense loop arrangement while maintaining image quality through effective decoupling
Solution Approach 2:
The harmful coupling effect is extracted and separated from the useful transmission function by introducing a dedicated decoupling conductor that handles only the coupling cancellation task, allowing the main conductor loops to focus on signal transmission
2Object-affected harmful factors
If preamplifier decoupling methods are used in transmit coil arrangements, then coupling between loops is reduced, but the method is not compatible with transmit system requirements
Solution Approach 1:
The decoupling approach is adapted from receive-to-transmit operation by changing the functional parameters: instead of using preamplifier-based decoupling suitable for receive modes, a power amplifier-based decoupling system is implemented that generates active cancellation fields compatible with transmit requirements
Solution Approach 2:
The decoupling mechanism is inverted from passive receive-mode decoupling to active transmit-mode decoupling, where power amplifiers generate currents to cancel coupling effects rather than relying on preamplifier impedance matching
3Object-affected harmful factors
If amplifier output is increased to compensate for coupling effects, then decoupling is achieved, but costs and device complexity increase excessively
Solution Approach 1:
A dedicated decoupling conductor acts as an intermediary that provides a separate pathway for coupling cancellation, allowing the main conductor loops to operate at normal power levels while the decoupling conductor handles the coupling compensation task
Solution Approach 2:
The amplifier system is segmented into separate functions: power amplifiers for signal transmission and dedicated decoupling amplifiers for coupling cancellation, allowing each subsystem to be optimized independently and reducing overall 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
Achieves better than 15 decibels of decoupling between elements, reducing SAR and enhancing image quality by allowing a denser arrangement of conductor loops for improved parallel transmission and faster k-space excitation.
Implementation Method 1
each group is bounded at least in a peripheral direction by at least one screen surface extending, for example, essentially in a radial and a longitudinal direction to decouple the groups
Implementation Method 2
measures to achieve adequate decoupling are known. Examples are the use of an overlap between adjacent conductor loops or a capacitor in a shared conductor of adjacent conductor loops
Implementation Method 3
the excitation field and the flip angle distribution may be shaped. At the same time, the SAR load for the object to be recorded (e.g., a patient) may also be reduced
Data Source
AI summary
A transmit coil arrangement for a magnetic resonance device includes a plurality of individually actuatable conductor loops following one after another in a peripheral direction and a longitudinal direction on a cylinder surface. At least two groups, at a distance from one another in the peripheral direction, of at least two conductor loops following one after the other in the longitudinal direction are provided in the peripheral direction. To decouple the at least two groups, each of the at least two groups is bounded at least in the peripheral direction by at least one screen surface extending essentially in a radial direction and the longitudinal direction.