Alternating Gradient Sequence for Quiet MRI
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Solution Overview
Problem
Current MRI scanners produce excessive acoustic noise during scanning, causing discomfort to patients, particularly in pediatric and elderly populations, due to vibrations in gradient coil structures induced by magnetic field changes, which existing noise-reduction techniques only partially address by reducing slew rates without significantly reducing the number of gradient transitions.
Innovation Solution
The method involves sampling k-space with pulse sequences that reduce the number of gradient transitions to one per repetition interval, allowing the previous readout gradient to serve as the next RF excitation selection gradient, while imposing slight rotations in projection angles to maintain motion correction and data consistency without requiring complex data processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional gradient sequences are used with multiple transitions per repetition interval, then spatial encoding and readout are achieved, but acoustic noise levels reach higher than 130 dBA causing patient discomfort
Solution Approach 1:
The patent applies periodic action by using alternating gradient sequences where gradients are applied periodically with only one transition per repetition interval instead of multiple transitions. This periodic gradient application reduces acoustic noise while maintaining the necessary spatial encoding functionality through the alternating positive and negative gradient lobes.
Solution Approach 2:
The patent changes the temporal parameters of gradient application by reducing the number of gradient transitions from multiple per repetition interval to just one transition. This parameter change in the gradient waveform structure significantly reduces acoustic noise generation while preserving image quality through alternative encoding schemes.
2Object-affected harmful factors
If the number of gradient transitions is reduced to one per repetition interval, then acoustic noise is substantially reduced, but spatial encoding capability must be maintained
Solution Approach 1:
The patent uses asymmetric gradient lobe configurations where the alternating positive and negative gradient lobes have different durations and amplitudes. This asymmetry allows the gradient sequence to provide both spatial encoding information and echo generation while maintaining only one transition per repetition interval, thus reducing noise while preserving image quality.
Solution Approach 2:
The patent employs dynamic gradient waveforms where the gradient amplitude and duration are varied within each repetition interval. The alternating gradient sequence dynamically adjusts gradient parameters to achieve both spatial encoding and signal generation functions with minimal transitions, maintaining image quality while reducing acoustic noise.
3Object-affected harmful factors
If gradient amplitude changes are made to reduce noise, then acoustic noise is reduced, but data consistency and motion correction capabilities may be compromised
Solution Approach 1:
The patent incorporates feedback mechanisms where the gradient sequence is designed to generate consistent echo signals that provide reference information for motion detection and correction. The alternating gradient pattern creates predictable signal variations that enable real-time monitoring and correction of motion artifacts, maintaining data consistency while reducing noise through fewer transitions.
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 substantially reduces acoustic noise while preserving motion correction capabilities and maintaining image quality, providing a more consistent and lower noise level compared to conventional techniques, allowing for efficient k-space data acquisition and accurate image reconstruction.
Implementation Method 1
current provided to gradient magnetic field coils for spatial encoding and readout during MRI data acquisition sequences
Implementation Method 2
this 'scanner noise' is produced by vibrations in the gradient coil related structures due to induced Lorentz forces which are proportional to the product of magnetic field strength and the gradient of amplitude changes
Data Source
AI summary
Magnetic resonance imaging (MRI) systems and methods to effect MRI data acquisition with reduced noise are described. A readout gradient, having a first polarity used to acquire and store MRI data in k-space memory during analog-to-digital conversion (ADC) of MR RF signals during one TR interval, is continued at substantially a same amplitude and vector direction and used as an image volume selection gradient during a transmitted RF excitation pulse that begins a next TR interval before the readout gradient transitions to an opposite polarity. The acquired k-space data is then used to generate an MR image.