RF Shield Slits for PET-MRI Eddy Current Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In hybrid PET-MRI systems, the RF shield generates high temperature profiles due to eddy current heating, which affects the performance of thermally sensitive parts like the PET detector array and patient comfort.
Innovation Solution
An RF shield with longitudinal and circumferential slits is designed to disrupt the formation of gradient field-induced eddy currents, reducing surface temperature by increasing impedance and preventing axial current build-up, while maintaining effective shielding and RF coil performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an RF shield is used to shield the PET detector array from RF fields, then shielding effectiveness is improved, but eddy current heating increases causing high temperature profiles on the shield surface
Solution Approach 1:
The RF shield is segmented by introducing longitudinal and circumferential slits that divide the continuous conductive surface into separate regions. This segmentation disrupts the eddy current paths, preventing large-scale current loops that generate excessive heat, while maintaining sufficient RF shielding effectiveness through the distributed slit structure.
Solution Approach 2:
The shield structure is modified with non-uniform slit distribution and varying slit dimensions across different regions. The longitudinal and circumferential slits are strategically positioned to create zones of different electrical properties, allowing the shield to simultaneously reduce eddy current heating in critical areas while maintaining RF shielding performance in other regions.
2Volume of moving object
If the RF shield is positioned close to the gradient coil for compact design, then device compactness is improved, but eddy current generation increases due to stronger gradient field coupling
Solution Approach 1:
The continuous RF shield surface is divided into segmented regions by longitudinal and circumferential slits, which interrupt the eddy current paths. This segmentation allows the shield to be positioned closer to the gradient coil without generating excessive eddy currents, as the disrupted current paths cannot form large loops even in strong gradient fields.
Solution Approach 2:
The slit structure acts as an intermediary element between the gradient coil and the RF shield, modifying the electromagnetic coupling. The slits create a controlled impedance structure that reduces the strength of eddy current induction while maintaining the physical proximity needed for compact system design.
3Temperature
If longitudinal and circumferential slits are introduced to reduce eddy currents, then temperature control is improved, but shielding effectiveness may be compromised
Solution Approach 1:
The slit structure is designed with varying dimensions, spacing, and distributions in different regions of the RF shield. This creates local variations in electrical properties that allow certain areas to prioritize eddy current reduction while other areas maintain stronger shielding characteristics, achieving both temperature control and shielding effectiveness simultaneously.
Solution Approach 2:
The RF shield with slits creates a composite electromagnetic structure that combines conductive regions (for shielding) and non-conductive gaps (for reducing eddy currents). This composite structure allows the shield to exhibit both RF blocking properties and reduced eddy current generation, resolving the contradiction between shielding effectiveness and temperature control.
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 effectively minimizes heat generation on the RF shield, protecting thermally sensitive components and maintaining image quality, thus enhancing the performance and comfort of hybrid PET-MRI systems.
Implementation Method 1
large amount of eddy-currents are created on the RF shield surface, with the pattern of these eddy current more or less mirroring the primary gradient current pattern
Implementation Method 2
the RF shield associated with the MRI scanner is positioned in between the RF body coil and the gradient coil to help prevent the high amplitude RF field being radiated out
Implementation Method 3
the RF shield associated with the MRI scanner is positioned in between the RF body coil and the gradient coil to help prevent the high amplitude RF field being radiated out, with the PET detector array being placed outside the RF shield in order to shield the sensitive detector array from the RF field
Data Source
AI summary
An imaging apparatus is disclosed that includes an MRI system, either as a stand-alone system or hybrid PET-MRI system. The MRI system includes gradient coils positioned about a patient bore, an RF coil former comprising an inner surface and an outer surface, an RF shield positioned on the outer surface of the RF coil former so as to be formed about the RF coil former, and an RF coil positioned on the inner surface of the RF coil former and about the patient bore, with the RF coil coupled to a pulse generator to emit an RF pulse sequence and receive resulting MR signals from a subject of interest. The RF shield includes a plurality of slits formed therein configured to disrupt the formation of gradient field induced eddy currents on the RF shield, so as to prevent the generation of high temperature profiles on the surface of the shield.