RF Coil Openings and Capacitors Reduce MRI Acoustic Noise
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems generate acoustic noise and vibration due to eddy currents induced in radio frequency (RF) coils by gradient coil operations, causing discomfort and potential harm to patients and operators.
Innovation Solution
The RF coil design incorporates a birdcage configuration with end ring sections and rungs, featuring openings and slits to minimize eddy currents, along with capacitors across slits to act as high impedance for eddy currents while maintaining RF performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gradient coils generate time-varying magnetic fields for spatial encoding, then MRI image quality and resolution are improved, but eddy currents are induced in the RF coil causing acoustic noise and vibration
Solution Approach 1:
The patent introduces a passive damping structure that converts the harmful eddy currents induced by gradient coils into a beneficial damping effect. The damping structure, made of conductive material with controlled electrical properties, transforms the unwanted eddy currents into heat through resistive damping, thereby reducing acoustic noise while preserving the necessary gradient field for image quality
Solution Approach 2:
The patent introduces a passive damping structure as an intermediary element between the gradient coils and the RF coil. This damping structure acts as a mediator that absorbs and dissipates the eddy currents induced in the RF coil by the gradient coils, preventing these currents from causing acoustic noise while not interfering with the gradient field's spatial encoding function
2Power
If the RF coil is designed with continuous conductive structure for optimal RF performance, then RF signal transmission is improved, but eddy currents are more readily induced causing increased acoustic noise
Solution Approach 1:
The patent applies local quality by making the RF coil structure non-uniform in specific locations. The passive damping structure is strategically positioned at locations where eddy currents are most problematic, creating localized variations in electrical conductivity and impedance that suppress eddy currents without significantly affecting the overall RF performance of the coil
3Object-generated harmful factors
If the RF coil structure is modified to reduce eddy currents through openings and slits, then acoustic noise is reduced, but RF performance may be degraded
Solution Approach 1:
The patent uses a passive damping structure that replicates the essential electromagnetic coupling function of the RF coil while having different electrical properties. The damping structure is designed with controlled electrical conductivity and geometric characteristics that allow it to couple with the RF field for damping purposes while maintaining the RF coil's primary function through separate 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 design effectively reduces acoustic noise and vibration, enhancing patient comfort and operational safety by minimizing eddy currents without degrading RF performance.
Implementation Method 1
The acoustic noise generated by the RF coil is typically caused by eddy currents induced in the RF coil conductors by the operation of the gradient coils
Implementation Method 2
capacitors coupled across the width of the slit... to act as high impedance for eddy currents
Implementation Method 3
Radio frequency (RF) coils are used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei
Implementation Method 4
gradient coils that produce smaller amplitude, spatially varying magnetic fields when a current is applied to them... designed to produce a magnetic field component that is aligned along the z axis, and that varies linearly in amplitude with position along one of the x, y or z axes
Implementation Method 5
the nuclear spins that are associated with the hydrogen nuclei in tissue water become polarized. This means that the magnetic moments that are associated with these spins become preferentially aligned along the direction of the main magnetic field, resulting in a small net tissue magnetization along that axis
Data Source
AI summary
A radio frequency (RF) coil for a magnetic resonance imaging (MRI) system includes a first end ring section containing a plurality of openings and a second end ring section containing a plurality of openings. A plurality of rungs is disposed between the first end ring section and the second end ring section. Each rung has a first end connected to the first end ring section and a second end connected to the second end ring section. Each rung can also include a plurality of openings. The openings in the end rings and rungs reduces eddy currents and improves RF performance of the RF coil.