MRI Gradient Coil Spatial Overlap Optimization
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Solution Overview
Problem
Existing MRI systems face challenges in optimizing gradient coil configurations to minimize peripheral nerve stimulation (PNS) and cardiac stimulation, which limits the performance of the gradient system.
Innovation Solution
The proposed solution involves designing a gradient coil arrangement where the maximum field regions of the coils in different spatial directions are optimized such that their spatial overlap is minimized, shifting the position of the field maxima to reduce stimulation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amplitude and rise time of gradient fields are increased to improve MRI performance, then the imaging speed and resolution are improved, but peripheral nerve stimulation and cardiac stimulation occur
Solution Approach 1:
The patent applies local quality by creating non-uniform current density distribution within the gradient coil windings. By strategically placing current sources and sinks at specific locations along the coil, the current density is concentrated in regions that generate beneficial gradient fields while minimizing regions that produce harmful electric fields in the patient's body. This localized optimization allows high gradient amplitudes without proportional increase in stimulation risk.
Solution Approach 2:
The patent transitions from optimizing single-axis gradient coils to a three-dimensional multi-axis gradient coil system. By coordinating the spatial and temporal characteristics of gradients along X, Y, and Z axes simultaneously, the system can achieve high overall gradient performance while distributing the stimulation risk across multiple dimensions. The vector sum of electric fields from all three axes is controlled to remain below stimulation thresholds even when individual axis gradients are strong.
2Measurement precision
If the amplitude and rise time of gradient fields are increased to improve MRI performance, then the imaging resolution is improved, but cardiac stimulation occurs
Solution Approach 1:
The patent applies local quality by creating non-uniform current density distribution within the gradient coil windings. By strategically placing current sources and sinks at specific locations along the coil, the current density is concentrated in regions that generate beneficial gradient fields while minimizing regions that produce harmful electric fields in the patient's body. This localized optimization allows high gradient amplitudes without proportional increase in stimulation risk.
Solution Approach 2:
The patent applies equipotentiality by designing the gradient coil structure and current distribution to minimize potential differences across the patient's body, particularly in the cardiac region. By carefully shaping the magnetic field gradients and controlling their spatial derivatives, the induced electric fields that could drive cardiac stimulation are reduced. The coil geometry and current patterns are optimized to create regions of relatively uniform electric potential near the patient's heart.
3Reliability
If the inductance of the gradient coil is increased to raise stimulation thresholds, then the stimulation performance is improved, but power losses increase
Solution Approach 1:
The patent applies parameter changes by optimizing multiple coil parameters simultaneously rather than increasing inductance alone. The current distribution pattern, winding geometry, and spatial arrangement of conductors are all adjusted to achieve high stimulation thresholds. By changing the current density profile and spatial distribution rather than simply increasing total inductance, the system achieves improved stimulation performance without the quadratic increase in resistive power losses that would result from higher currents or larger inductances.
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 allows for safer and more effective MRI scans by reducing the stimulation of patients while maintaining the performance of the gradient system, without compromising coil quality or increasing power losses.
Implementation Method 1
each gradient coil (23, 22) being designed such that its magnetic gradient field has a maximum field region
Implementation Method 2
MRI devices expose patients to time-dependent magnetic gradient fields, which, however, can generate electric fields within the patient's body
Data Source
AI summary
A gradient coil arrangement of an MRI system is described that defines a first and at least one second axis in different spatial directions. Disposed in each spatial direction is at least one gradient coil which generates a magnetic gradient field along the respective axis. The magnetic gradient fields each have a maximum field region which corresponds to a region in which the field strength attains a predetermined percentage of the maximum strength. The gradient coil of the first axis is configured such that the overlap of its maximum field region with that of the at least one second axis is less than a limit value.