Mobile MRI Permanent Magnet Field Stabilization
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Solution Overview
Problem
Existing MRI systems face limitations such as high cost, size, and weight due to the use of high-field superconducting magnets, which also result in increased specific absorption rate (SAR) and image artifacts.
Innovation Solution
A mobile MRI system utilizing a permanent magnet to provide a stable low-field magnetic environment, combined with efficient methods for pulse transmission and signal reception, including the use of class-D power amplifiers, detuning and damping circuits, and parallel-tuned coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If superconducting magnets are used to produce high magnetic fields, then signal-to-noise ratio is improved, but device size and weight increase
Solution Approach 1:
The patent changes the magnetic field strength parameter from high field (1.5T, 3T, 7T) to low field (using permanent magnets), thereby reducing magnet weight and size while accepting lower signal-to-noise ratio and requiring longer relaxation times for imaging
Solution Approach 2:
The patent replaces expensive superconducting magnets with cheaper permanent magnets, making the system more cost-effective and suitable for mobile applications, though requiring longer scan times to compensate for lower signal quality
2Measurement precision
If superconducting magnets are used to produce high magnetic fields, then signal-to-noise ratio is improved, but specific absorption rate increases
Solution Approach 1:
The patent reduces the static magnetic field strength parameter from high field to low field, which directly reduces the specific absorption rate (SAR) that scales with B0², making the system safer for patients with implanted devices
3Measurement precision
If superconducting magnets are used to produce high magnetic fields, then signal-to-noise ratio is improved, but image artifacts around metallic devices increase
Solution Approach 1:
The patent reduces the magnetic field strength parameter from high field to low field, which reduces the magnetic susceptibility effects that cause image artifacts around metallic implants and devices
4Weight of stationary object
If permanent magnets are used to reduce device size and weight, then mobility is improved, but magnetic field stability deteriorates
Solution Approach 1:
The patent implements a feedback mechanism using a frequency measurement module to monitor the Larmor frequency and detect magnetic field drift, with a compensation module that adjusts the field in real-time to maintain stability despite using permanent magnets
Solution Approach 2:
The patent performs preliminary field mapping and characterization of the permanent magnet system to establish baseline parameters and compensation strategies before actual imaging begins
5Weight of stationary object
If low-field permanent magnets are used to enable mobility, then device portability is improved, but tissue relaxation times increase
Solution Approach 1:
The patent uses periodic RF pulse sequences designed for low-field conditions, with optimized repetition times that account for the longer T1 relaxation at low fields, enabling mobile imaging despite extended scan durations
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
The system achieves improved image quality with reduced acoustic noise, shorter tissue relaxation times, and increased B1 homogeneity, making it suitable for point-of-care diagnostics and research.
Implementation Method 1
providing, by the permanent magnet of the mobile MRI device, a main static magnetic field
Implementation Method 2
providing, by a frequency measurement module of the mobile MRI device, a radiofrequency pulse to induce a free induction decay (FID) signal
Data Source
AI summary
Methods and apparatus are provided to implement low-field MRI systems, which may be accessible and mobile in clinic offices and ICU for point-of-care. The low-field MRI systems are enabled by several features. A mobile magnet provides a stable B0 field generated by permanent material. To increase the stability of the B0 field, a monitoring coil and shimming coil are operated in combination. Further, several non-50 Ohm circuit methods are provided for use in the mobile MRI system. Transmit circuits provided include different damping and detuning circuits. In a receive channel, a receive coil array using parallel-tuned circuits is provided to implement a multi-channel receive. Further, decoupling and off-coil detuning strategies are provided.