Shielded Gradient Coil Assembly With Hybrid Cooling
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Solution Overview
Problem
Existing shielded gradient assemblies face challenges in optimizing performance due to overheating from Ohmic and eddy current losses, with conventional cooling methods either inefficiently cooling the conductors or increasing eddy currents, leading to reduced efficiency and electromagnetic performance.
Innovation Solution
The shielded gradient assembly employs a hybrid cooling system where gradient field coils have hollow conductors with smaller cross sections for direct cooling and gradient shield coils have larger cross sections for indirect cooling, with both types of coils arranged coaxially to minimize eddy currents and enhance cooling capacity where needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cooling methods are used to cool the conductors, then cooling capacity is provided, but eddy currents increase leading to overheating and reduced efficiency
Solution Approach 1:
The patent applies different cooling strategies to different coil systems: the gradient field coils use hollow conductors with direct internal fluid cooling to maximize cooling efficiency where eddy currents are highest, while the gradient shield coils use indirect external cooling. This localized differentiation optimizes cooling capacity while minimizing eddy current losses in each specific region.
Solution Approach 2:
The cooling system is segmented into two independent pathways: one for gradient field coils with internal hollow conductors and another for gradient shield coils with external cooling channels. This segmentation allows each coil type to be cooled optimally according to its specific electromagnetic characteristics and eddy current generation patterns.
2Temperature
If larger cross section conductors are used in shield coils for indirect cooling, then cooling capacity is enhanced, but eddy current susceptibility increases
Solution Approach 1:
The patent recognizes that the gradient shield coils operate in regions with lower magnetic flux density compared to gradient field coils, allowing them to use larger cross-section conductors with external cooling channels. The lower flux environment reduces eddy current generation, making indirect cooling effective without excessive eddy current losses.
3Loss of energy
If hollow conductors with smaller cross sections are used in gradient field coils, then eddy currents are suppressed, but cooling capacity is reduced
Solution Approach 1:
The patent employs hydraulic cooling by passing fluid directly through the hollow conductors of the gradient field coils. This internal fluid flow provides efficient heat removal from the high-eddy-current regions, compensating for the smaller conductor cross-section and maintaining effective cooling capacity.
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 design effectively reduces eddy currents and overheating, allowing for higher gradient strength, improved patient throughput, and enhanced electromagnetic performance by optimizing cooling based on magnetic flux density.
Implementation Method 1
Fluid coolant may be passed through the hollow electrical conductors for direct cooling when electrical current passes though the electrical conductors
Implementation Method 2
a gradient shield coil arrangement that compensates the gradient magnetic fields outward form the shielded gradient assembly
Implementation Method 3
the gradient field coil arrangement has sets of electrical conductors to generate gradient magnetic fields in the longitudinal (z), and two transverse (x,y) directions
Implementation Method 4
The smaller cross section suppresses the generation of eddy currents in the gradient coil. Additionally the generation of eddy currents in in components outside the gradient coils due to switching of the electrical currents
Data Source
AI summary
A shielded gradient coil assembly (40) to generate a gradient magnetic field, the assembly comprises on a plurality of radially inner and outer coaxial cylindrical surfaces a gradient field coil arrangement on the radially inner cylindrical surfaces including a longitudinal gradient field coil system (131) having one or more axial circumferential electrically conducting hollow z-field windings having a smaller transverse cross-section and a transverse gradient field coil system (132) having hollow (x,y)—field electrical conductors having a smaller transverse cross-section and arranged as saddle coils on the surfaces of the inner cylindrical surfaces. A gradient shield coil arrangement is provided on the radially outer cylindrical surfaces including a longitudinal gradient shield coil system (141) having one or more axial circumferential electrically conducting hollow z-shield windings having a larger transverse cross-section and a transverse gradient shield coil system (142) having solid electrical conductors arranged as saddle coils on the surfaces of the outer cylindrical surfaces. In this way an optimum combination is achieved of efficient direct and indirect cooling of the conductors while keeping eddy current effects at a low level.