NMR Gradient Coils in Tubes with Cryogenic Screen
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Solution Overview
Problem
Nuclear magnetic resonance (NMR) machines face challenges in producing high-intensity, homogeneous gradients while minimizing eddy currents, noise, and power dissipation, which affects imaging quality and patient comfort, particularly in high-field MRI applications.
Innovation Solution
The use of solenoidal gradient coils incorporated into tubes within an annular cylindrical space, combined with a conductive cylindrical screen cooled to low temperatures, to manage eddy currents and enhance gradient intensity and linearity, allowing for controlled induction of currents that reinforce the gradients produced by the solenoidal coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gradient coils are made larger to increase gradient homogeneity, then gradient quality improves, but device size and power consumption increase
Solution Approach 1:
The patent places solenoidal gradient coils inside tubes that are positioned within the annular cylindrical space between the cryostat and the usable interior space. This nested arrangement allows the gradient coils to be incorporated into the existing structural space without increasing the overall device footprint, while still achieving the required gradient homogeneity through optimized coil design and positioning.
2Manufacturing precision
If gradient coils are made larger to increase gradient homogeneity, then gradient quality improves, but power dissipation increases
Solution Approach 1:
By nesting the gradient coils within the annular cylindrical space between the cryostat and the usable interior space, the patent eliminates the need for additional power-intensive coil windings that would be required if conventional external coils were used. This nested configuration achieves gradient homogeneity with reduced power dissipation.
3Productivity
If gradient pulses are made faster to improve imaging speed, then productivity increases, but electromagnetic forces and noise increase
Solution Approach 1:
The patent introduces a conductive cylindrical screen cooled to low temperatures (below 77 K) that is positioned between the gradient coils and the cryostat. This screen converts the harmful eddy currents generated by fast gradient pulses into beneficial effects: the cooled conductive screen suppresses parasitic eddy currents that would otherwise generate noise and electromagnetic forces, while allowing the gradient fields to pass through effectively. The low temperature reduces thermal agitation and stabilizes the screen's conductive properties during rapid gradient switching.
4Power
If gradient coils are positioned to produce strong gradients, then gradient intensity improves, but eddy currents in the cryostat increase
Solution Approach 1:
The conductive cylindrical screen acts as an intermediary element positioned between the gradient coils and the cryostat. This screen mediates the interaction between the gradient fields and the cryostat structure, allowing strong gradient fields to be produced while suppressing eddy currents in the cryostat through its cooled conductive properties. The screen serves as a barrier that controls electromagnetic field distribution and prevents direct coupling between the gradient coils and the cryostat.
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 configuration reduces noise and power consumption, improves gradient linearity and intensity, and maintains patient comfort by minimizing eddy currents and acoustic noise, while allowing for efficient cooling and effective gradient production in high-field MRI applications.
Implementation Method 1
gradient coils superimpose additional magnetic fields on the intense main field
Implementation Method 2
solenoidal gradient coils which are incorporated into tubes
Implementation Method 3
the eddy currents induced in the cylindrical screen contribute to reinforcing the gradients produced by said solenoidal gradient coils
Implementation Method 4
such that negligible induced currents are generated in the exterior cryogenic enclosure while the eddy currents induced in the cylindrical screen contribute to reinforcing the gradients
Implementation Method 5
a cylindrical screen along the axis Z comprising a conductive material cooled to a temperature less than or equal to 77 kelvins (K)
Implementation Method 6
efficient cooling
Data Source
AI summary
The nuclear magnetic resonance machine comprises a device (101) for creating an intense main magnetic field B0 in a usable interior space (109) in the form of a tunnel with axis Z, a radio-frequency excitation device that also processes radio-frequency signals emitted in response by a body (150) placed in the usable interior space (109), and a set (110) of solenoidal gradient coils for superimposing on the intense magnetic field B0 components of a additional magnetic field, the gradient coils (111-122) being incorporated into tubes disposed in an annular cylindrical space (130). Between an exterior cryogenic enclosure (102) and the annular cylindrical space (130) a cylindrical screen (104) is disposed along the axis Z comprising a conductive material of low resistance and low magnetoresistance such that negligible induced currents are generated in the exterior cryogenic enclosure (102) while the eddy currents induced in the cylindrical screen (104) contribute to reinforcing the gradients produced by the solenoidal gradient coils (111-122).