Dielectric Assembly for MRI Gradient Coil PNS Reduction
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems are limited by peripheral nerve stimulation (PNS) due to rapidly changing magnetic fields, which restrict gradient coil performance and scan quality, as conventional methods set thresholds that do not account for individual variations in sensitivity.
Innovation Solution
A method involving the use of a dielectric assembly positioned adjacent the skin surface to attenuate local electric fields, allowing for increased gradient coil settings above the PNS threshold without inducing stimulation, enabling safer operation of MRI systems with higher gradient amplitudes and faster slew rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gradient coil settings are increased above conventional PNS thresholds, then MRI performance is improved through faster slew rates and greater gradient strengths, but peripheral nerve stimulation is induced in most subjects
Solution Approach 1:
A dielectric assembly is introduced as an intermediary between the gradient coil and the subject's body. This dielectric material modifies the distribution of induced electric fields, creating a protective effect that allows higher gradient settings without inducing PNS in most subjects. The dielectric assembly acts as a mediator that decouples the direct relationship between gradient coil output and nerve stimulation risk.
Solution Approach 2:
The invention changes the physical parameters of the interaction by introducing a dielectric material with specific permittivity properties. This alters the electric field distribution and reduces the effective stimulation threshold at the nerve tissue, enabling operation at higher gradient amplitudes and slew rates without exceeding safe stimulation levels.
2Reliability
If gradient slew rates and amplitudes are limited to prevent PNS, then subject comfort is maintained, but scan times are extended and image quality is reduced
Solution Approach 1:
The dielectric assembly serves as a protective intermediary that allows the system to operate at higher performance settings while maintaining subject comfort. By modifying the electric field distribution, it creates a safety margin that enables faster imaging without compromising subject well-being.
Solution Approach 2:
The dielectric assembly is positioned on the subject before the high-performance gradient sequence is executed. This preliminary placement of the protective material ensures that when high slew rates and amplitudes are applied, the subject is already protected, allowing immediate use of optimized scan parameters without needing to lower them for comfort reasons.
3Reliability
If empirical PNS thresholds are used for gradient coil operation, then most subjects are protected from stimulation, but individual variations in sensitivity cannot be accommodated
Solution Approach 1:
The dielectric assembly provides a universal protective effect that works across different individuals regardless of their specific sensitivity variations. By introducing this external protective element, the system no longer relies solely on individual threshold variations but instead uses a consistent physical intervention that protects all subjects, enabling higher standardized gradient settings for everyone.
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 approach effectively increases the PNS threshold, allowing for the use of previously unattainable gradient coil settings, enhancing MRI performance by reducing discomfort and improving image quality and scan efficiency.
Implementation Method 1
A dielectric assembly is positioned adjacent a skin surface of a subject... such that the dielectric assembly attenuates the local electric fields induced by the magnetic field gradients
Implementation Method 2
Rapidly changing magnetic fields produce electric fields that can stimulate nerves in the body
Data Source
AI summary
Systems and methods for imaging a subject with a magnetic resonance imaging system using magnetic field gradients generated by one or more gradient coils operating with gradient coil settings, such as gradient amplitudes and gradient slew rates, above a threshold at which peripheral nerve stimulation is likely to be induced in the subject. A dielectric assembly is positioned adjacent a skin surface of the subject such that the dielectric assembly attenuates the local electric fields induced by the magnetic field gradients, which would be likely to induce PNS when the dielectric assembly is not arranged adjacent the skin surface of the subject. As a result of the dielectric assembly placed adjacent the skin surface of the subject, the gradient coil settings can be increased above the threshold without inducing PNS in the subject.