MRI Gradient Waveform Distortion Correction
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Solution Overview
Problem
Existing MRI techniques fail to correct distortions in the k-space caused by waveform distortion of the gradient magnetic field pulse in both the readout and phase encoding directions, leading to artifacts in reconstructed images.
Innovation Solution
A magnetic resonance imaging apparatus that uses a pulse sequence to repeatedly measure echoes with varying dephasing pulse time integral values, allowing for the calculation of correction information to eliminate distortions in both the readout and phase encoding directions by determining shift amounts of echo peaks in both directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a readout gradient magnetic field pulse is applied in high-speed imaging methods (EPI, BASG) to shorten imaging time, then imaging speed is improved, but waveform distortion occurs causing k-space distortion and image artifacts
Solution Approach 1:
The patent applies preliminary action by measuring the actual waveform of the readout gradient magnetic field pulse before image reconstruction and calculating the distortion amount in advance. This allows the distortion characteristics to be characterized beforehand, so that correction can be applied during reconstruction without compromising imaging speed. The waveform measurement and distortion calculation are performed as preliminary steps that enable subsequent artifact-free reconstruction.
2Measurement precision
If the phase encoding gradient magnetic field pulse amplitude is increased to improve positional information accuracy, then measurement precision is improved, but eddy current distortion in the phase encoding direction increases
Solution Approach 1:
The patent implements feedback by measuring the actual echo signals that contain distortion information from both readout and phase encoding directions, then using this measured data to calculate correction amounts. The distortion characteristics are fed back into the reconstruction process, allowing the system to compensate for eddy current effects that would otherwise degrade image quality. This feedback mechanism enables accurate correction without requiring changes to the original pulse amplitudes.
3Manufacturing precision
If waveform measurement and distortion correction are applied to eliminate k-space distortion, then image quality is improved, but processing complexity increases
Solution Approach 1:
The patent applies self-service by using the echo signals themselves to carry distortion information, which then serves to correct the distortion. The measured echo data, which would normally just be processed for reconstruction, is instead utilized to automatically determine the distortion characteristics and generate correction factors. This self-correcting mechanism eliminates the need for separate complex measurement systems while improving image quality.
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 distortions in both directions, improving image quality by suppressing artifacts and enhancing the accuracy of k-space data arrangement, particularly in high-speed imaging methods.
Implementation Method 1
output characteristics of a gradient magnetic field amplifier itself, inductance of a gradient coil
Implementation Method 2
eddy current induced by application of the gradient magnetic field pulse
Implementation Method 3
signals generated from the subject by the nuclear magnetic resonance are measured
Data Source
AI summary
In order to improve image quality, a technique for obtaining information for eliminating distortions of the k-space in the readout direction and the phase encoding direction caused by the waveform distortion of the gradient magnetic field pulse is provided. A pulse sequence for the main scan is used to repeatedly measure echoes with changing the time integral value of the dephasing pulse for the readout gradient magnetic field. In the above measurement, the phase encoding pulse is not made zero, but two-dimensional data are measured in the same manner as that of the main scan. By using the measured two-dimensional data, correction information for eliminating distortions of the k-space in the readout direction and the phase encoding direction caused by the waveform distortion of the gradient magnetic field pulse is calculated in each of the readout direction and the phase encoding direction.