MRI Gradient Coil Distortion Correction via Off-Center Reference
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Solution Overview
Problem
The increasing demand for stronger gradient magnetic fields and higher slew rates in MRI systems leads to non-linearity in the gradient magnetic field, causing image distortion due to the narrowing of the linear region, which conventional correction tables and methods fail to adequately address, resulting in residual errors.
Innovation Solution
The MRI apparatus generates distortion correction data to convert the non-linear characteristic of the gradient magnetic field into a linear one using a correction reference position away from the magnetic field center, ensuring linearity over a wider range by aligning the calibration and correction positions, thereby reducing residual errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the gradient magnetic field strength is increased to meet higher imaging demands, then the imaging capability is improved, but the linear region of the gradient magnetic field is narrowed causing image distortion
Solution Approach 1:
The invention changes the reference position parameter from the magnetic field center to a position away from the center. By setting the reference position at a location where the gradient magnetic field exhibits non-linear characteristics, the correction table can compensate for non-linearity in the wider imaging region, allowing higher gradient strength while maintaining image accuracy.
2Productivity
If the slew rate of the gradient pulse is increased to improve imaging speed, then the productivity is improved, but the non-linearity of the gradient magnetic field increases causing image distortion
Solution Approach 1:
The invention changes the reference position parameter for slew rate correction from the magnetic field center to a position away from the center. This allows the correction table to effectively compensate for non-linearity caused by high slew rates in the imaging region, enabling faster imaging while maintaining image accuracy.
3Device complexity
If a conventional correction table using the magnetic field center as reference is used, then the device complexity is kept simple, but residual errors remain in the corrected image
Solution Approach 1:
The invention changes the reference position parameter in the correction table from the magnetic field center to a position away from the center. This simple parameter change enables the correction table to effectively compensate for non-linearity in the imaging region, significantly reducing residual errors while maintaining system simplicity.
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 effectively corrects image distortions caused by non-linearity, maintaining image accuracy even when the gradient magnetic field strength or slew rate increases, by ensuring the correction reference position matches the calibration position, thus minimizing residual errors and maintaining image fidelity.
Implementation Method 1
A gradient magnetic field is generated by, for example, a cylindrical gradient coil. Normally, the gradient magnetic field changes linearly in the vicinity of the axial center of the gradient coil (i.e., in the vicinity of the magnetic field center) but exhibits a non-linear change as the distance from the magnetic field center increases.
Implementation Method 2
the MRI apparatus obtains the frequency (or phase) of each of the acquired MR signals and the signal intensity at the obtained frequency (or phase) by reconstruction processing based on, for example, inverse Fourier transform
Implementation Method 3
An MRI apparatus is an imaging apparatus that magnetically excites nuclear spin of an object placed in a static magnetic field by applying a radio frequency (RF) pulse having the Larmor frequency and reconstructs an image on the basis of magnetic resonance (MR) signals emitted from the object due to the excitation.
Data Source
AI summary
In one embodiment, an MRI apparatus includes: a scanner that is provided with at least an RF coil and a gradient coil and is configured to acquire a magnetic resonance (MR) signal emitted from an object in response to applications of an RF pulse outputted from the RF coil and a gradient magnetic field generated by the gradient coli; and processing circuitry configured to reconstruct a diagnostic image of the object based on the MR signal, generate distortion correction data for correcting a non-linear characteristic of the gradient magnetic field to a linear characteristic that is defined by gradient magnetic field strength at a correction position away from a magnetic field center of the gradient coil and distance from the magnetic field center to the correction position, and correct the diagnostic image by using the distortion correction data.