Cryogenic Current Sensor for MRI Magnet B0 Compensation
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Solution Overview
Problem
Existing B0 compensation systems for MRI scanners face challenges in achieving accurate and adjustable magnetic field stabilization, particularly due to difficulties in positioning magnetic field sensors and fixed gain responses, leading to increased manufacturing complexity and cost.
Innovation Solution
A superconducting magnet system with a cryogenic electric current sensor inside the magnet cryostat, which measures electric current flowing in the superconducting B0 compensation circuit, enabling active B0 compensation without the need for a magnetic field sensor in the imaging FOV and allowing adjustable shield factor and frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic field sensor is installed in or near the imaging FOV for active B0 compensation, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent introduces an intermediary approach by using a magnetic field sensor located outside the magnet cryostat that couples to the B0 compensation circuit through magnetic coupling. This intermediary sensor position avoids the complexity of positioning sensors inside the FOV while still enabling accurate measurement of B0 field variations through the magnetic coupling mechanism between the sensor and the compensation circuit.
2Reliability
If passive B0 compensation systems use electrical connection with magnet windings, then shield factor is improved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces direct electrical connections with magnetic coupling as an intermediary mechanism. The B0 compensation circuit is magnetically coupled to the magnet windings rather than electrically connected, which simplifies manufacturing by eliminating the need for strategic electrical connections within winding coils while maintaining effective B0 compensation through the magnetic coupling field.
3Ease of manufacture
If passive B0 compensation systems use inductive coupling, then ease of manufacture is improved, but shield factor decreases
Solution Approach 1:
The patent creates a copied or surrogate sensing mechanism by placing a magnetic field sensor outside the cryostat that replicates the function of an internal sensor through magnetic coupling. This copied approach maintains the simplicity of external sensor installation while achieving the measurement precision normally requiring internal sensor placement, thereby resolving the trade-off between ease of manufacture and compensation effectiveness.
4Device complexity
If active B0 compensation uses frequency adjustment in software, then device complexity is reduced, but measurement precision requirements increase
Solution Approach 1:
The patent uses magnetic coupling as an intermediary that enables the external sensor to achieve sufficient measurement precision for active B0 compensation without requiring complex internal sensor positioning. The magnetic coupling mechanism amplifies or transfers the B0 field variations to the external sensor, allowing software-based frequency adjustment to work effectively with reduced hardware complexity while maintaining the required measurement precision.
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 solution reduces manufacturing costs, relaxes design constraints, and provides effective B0 compensation with reduced thermal noise, enabling improved image quality by synergistically combining passive and active compensation methods.
Implementation Method 1
superconducting magnet coils disposed inside the magnet cryostat and configured to generate a static (B0) magnetic field when an electric current flows in the superconducting magnet coils
Implementation Method 2
superconducting magnet coils disposed inside the magnet cryostat and configured to generate a static (B0) magnetic field when an electric current flows in the superconducting magnet coils
Implementation Method 3
These designs are based on the principle that a superconducting circuit keeps its magnetic flux constant
Implementation Method 4
Some passive B0 compensation systems are described in, e.g. Reichert, U.S. Pat. No. 4,926,289 ('Actively shielded, superconducting magnet of an NMR tomography apparatus') and Overweg, U.S. Pat. No. 5,426,366 ('Magnetic resonance apparatus comprising a superconducting magnet')
Implementation Method 5
an electric current sensor disposed inside the magnet cryostat and connected to measure electric current flowing in the superconducting B0 compensation circuit
Implementation Method 6
an electric current sensor disposed inside the magnet cryostat and connected to measure electric current flowing in the superconducting B0 compensation circuit
Implementation Method 7
the superconducting magnet windings are immersed in liquid helium (LHe) contained in a vacuum-jacketed LHe dewar or are disposed in some other type of cryostat to maintain the windings at suitably low cryogenic temperature
Implementation Method 8
the superconducting magnet windings are immersed in liquid helium (LHe) contained in a vacuum-jacketed LHe dewar
Data Source
AI summary
A superconducting magnet includes superconducting magnet coils (C1, C2, C3, C4, C5, C6, S1, S2) disposed inside a magnet cryostat (12). The superconducting magnet coils generate a static (B0) magnetic field when an electric current flows in the superconducting magnet coils. A superconducting B0 compensation circuit (30, 60, 70) is also disposed inside the magnet cryostat, and is coupled with the superconducting magnet coils to passively reduce temporal variations in the B0 magnetic field generated by the superconducting magnet coils. An electric current sensor (40) is also disposed inside the magnet cryostat and is connected to measure electric current flowing in the superconducting B0 compensation circuit. An active B0 compensation component (50) is operatively connected with the electric current sensor to receive the measurement of electric current flowing in the superconducting B0 compensation circuit and to provide active B0 magnetic field compensation based on the measured electric current.