MRI Gradient Coil Noise Reduction via Pulse Waveform Modulation

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Solution Overview

Problem

Magnetic resonance imaging (MRI) apparatuses experience high-frequency noise due to mechanical strain in gradient magnetic field devices, causing discomfort to subjects during imaging, as the gradient magnetic field repeatedly rises and falls in short repetition intervals.

Innovation Solution

A magnetic resonance imaging apparatus that includes a gradient magnetic field device and a measurement control unit, which changes the waveform of the gradient magnetic field pulses to lengthen the application interval, shifting the noise frequency from high to low frequencies by reversing polarity, increasing pulse width, altering application timing, or modifying pulse strength, thereby reducing discomfort.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the repetition interval of gradient magnetic field pulses is shortened to improve imaging speed, then productivity is improved, but high-frequency noise increases causing discomfort to subjects

Engineering Contradiction:

Improveimaging speedVSAvoidnoise discomfort

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the waveform parameters of the gradient magnetic field pulse, specifically modifying the pulse shape and repetition pattern to shift the noise frequency spectrum from high frequency to low frequency range, thereby reducing subject discomfort while maintaining short repetition intervals for efficient imaging

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs periodic modulation of the gradient magnetic field pulse waveform, using structured repetition patterns that create predictable noise cycles at lower frequencies, making the noise more tolerable for subjects while preserving the rapid imaging capability

Inventive Principle:

Principle #19Periodic action

2Loss of time

If the gradient magnetic field pulse repetition rate is increased to reduce scanning time, then loss of time is reduced, but noise frequency increases causing severe discomfort

Engineering Contradiction:

Improvescanning timeVSAvoidnoise discomfort

Core Design Contradiction:

Loss of timeVSObject-affected harmful factors

Solution Approach 1:

The patent modifies the temporal parameters of the gradient magnetic field pulses, adjusting pulse width, spacing, and waveform shape to redistribute the spectral content of generated noise toward lower frequencies, thereby maintaining fast scanning while reducing high-frequency noise discomfort

Inventive Principle:

Principle #35Parameter changes

3Productivity

If conventional gradient magnetic field pulses are used with short repetition intervals, then imaging efficiency is improved, but noise with high frequency occurs causing severe discomfort

Engineering Contradiction:

Improveimaging efficiencyVSAvoidhigh-frequency noise

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent systematically varies the waveform parameters of the gradient magnetic field pulses including amplitude modulation, pulse shaping, and timing adjustments to shift the dominant noise frequencies from the high-frequency range to low-frequency range, maintaining imaging efficiency while reducing subject discomfort

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful high-frequency noise into less harmful low-frequency noise by manipulating the pulse waveform characteristics, effectively transforming the nature of the adverse effect while preserving the beneficial rapid imaging capability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 solution effectively shifts high-frequency noise to low frequencies, reducing the sense of discomfort for subjects by distributing noise energy across a wider frequency range, making the imaging process more tolerable.

Implementation Method 1

When gradient magnetic fields are generated, electromagnetic forces are generated in gradient magnetic field coils and the electromagnetic forces cause the gradient magnetic field devices including the gradient magnetic field coils to generate mechanical strain, and thus noise occur from the gradient magnetic field devices

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Implementation Method 2

The measurement control unit performs noise suppression control to shift a frequency of noise generated by the gradient magnetic field device to a low frequency side by changing a waveform of the gradient magnetic field pulse

Methodology Applied

Scientific EffectWaveform modulation: Phase Modulation

Data Source

PatentUS10393834B2Magnetic resonance imaging apparatus and noise reduction method

Publication Date: 2019.08.27 FUJIFILM CORP

AI summary

To supply a magnetic resonance imaging (MRI) apparatus capable of shifting a high frequency of noise into a low frequency during measurement, the magnetic resonance imaging apparatus includes: a gradient magnetic field device (9, 10) that applies a pulse-shaped gradient magnetic field to an object placed in a static magnetic field; and a measurement control unit (4) that drives the gradient magnetic field device by a gradient magnetic field pulse and measures magnetic resonance image data. The measurement control unit performs noise suppression control to shift a frequency of noise generated by the gradient magnetic field device to a low frequency side by changing a waveform of the gradient magnetic field pulse during repetition of the gradient magnetic field pulses at a constant period.