MRI RF Shield Slits for Eddy Current Reduction
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Solution Overview
Problem
In magnetic resonance imaging (MRI) apparatuses, eddy currents induced by the gradient magnetic field on RF shields can cause image deterioration, and existing solutions either compromise RF shielding performance or fail to effectively segment eddy currents.
Innovation Solution
The RF shield is configured with a plurality of slits of asymmetrical lengths and positions, alternating in the axial direction along the circumferential direction, to lengthen the pathway of eddy currents and reduce their induction while maintaining effective RF magnetic field shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an RF shield is provided to block RF magnetic field, then RF shielding performance is improved, but eddy currents are induced by gradient magnetic field causing image deterioration
Solution Approach 1:
The RF shield is divided into multiple segments with slits introduced at specific positions. These slits segment the continuous conductive path of the RF shield, thereby interrupting and reducing eddy current circulation while preserving RF magnetic field shielding capability through maintained electrical connectivity in controlled regions.
Solution Approach 2:
The slits are positioned asymmetrically with respect to the axial center of the RF shield. This asymmetric arrangement optimizes the interruption of eddy current paths generated by gradient magnetic fields while maintaining effective RF shielding performance, as the asymmetric positioning strategically breaks harmful current loops without compromising overall shield integrity.
2Object-generated harmful factors
If slits are introduced to segment eddy currents, then eddy current induction is reduced, but RF shielding performance may be compromised
Solution Approach 1:
The slits are positioned at specific localized regions of the RF shield rather than uniformly distributed. This local quality approach ensures that eddy current segmentation occurs at strategically chosen positions while maintaining continuous shielding coverage in other critical areas, thus reducing eddy currents without compromising overall RF shielding performance.
Solution Approach 2:
The slits extend in the axial direction of the RF shield, introducing a dimensional aspect to the segmentation strategy. By orienting slits along the axial dimension rather than circumferentially, the design effectively interrupts eddy current paths generated by gradient fields while preserving radial and circumferential shielding continuity for RF magnetic fields.
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 effectively reduces the induction of eddy currents, thereby improving image quality by minimizing their impact on the MRI apparatus without compromising the RF shielding performance.
Implementation Method 1
a radio frequency (RF) shield may be provided to block off an RF magnetic field generated from an RF coil toward a gradient coil side
Implementation Method 2
an eddy current is induced by a gradient magnetic field applied from the gradient coil
Implementation Method 3
an eddy current is induced by a gradient magnetic field applied from the gradient coil. This eddy current may provide causes of image deterioration
Data Source
AI summary
A magnetic resonance imaging apparatus according to an embodiment includes an RF coil and an RF shield. The RF coil is formed in a substantially cylindrical shape. The RF shield is formed in a substantially cylindrical shape and is disposed on an outer circumferential side of the RF coil. The RF shield is provided with a plurality of slits that are in a form of a line extending in an axial direction and having an asymmetrical length in the axial direction with respect to a center in the axial direction and are disposed so as to alternately switch positions thereof in the axial direction along a circumferential direction.