MRI Gradient Pulse Waveform Synthesis for Noise Reduction

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Solution Overview

Problem

Conventional MRI techniques struggle to suppress gradient magnetic field noise effectively while maintaining high flexibility in pulse sequence design, especially at high magnetic field intensities, leading to unpleasant noise levels for patients and limitations in imaging conditions.

Innovation Solution

The use of a gradient magnetic field pulse with a synthesized waveform formed from multiple base waves, which have a smoothly changing convex upward shape, allowing for the same silencing effect as sine waves while maintaining the time integral and application time of traditional triangular or trapezoidal waveforms, thus enabling flexible pulse sequence design without affecting other imaging parameters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a low pass filter is used to smooth the gradient magnetic field waveform to suppress noise, then noise intensity is reduced, but application time becomes longer which is incompatible with fast pulse sequences

Engineering Contradiction:

Improvenoise intensityVSAvoidapplication time

Core Design Contradiction:

Object-affected harmful factorsVSDuration of action of moving object

Solution Approach 1:

The invention changes the waveform shape parameter from conventional trapezoidal to synthesized waveform with smooth convex upward portions. This parameter change in waveform morphology suppresses noise by reducing abrupt transitions while maintaining the same application time, thus resolving the contradiction between noise reduction and time efficiency in fast pulse sequences

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention applies curvature by designing gradient magnetic field pulses with smoothly curved convex upward portions instead of straight-line transitions. This curvature in the waveform reduces high-frequency components that cause noise while preserving the pulse duration, enabling noise suppression without extending application time

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Object-affected harmful factors

If sine waveforms are used for readout and phase encoding gradients to reduce noise, then noise is suppressed, but maximum intensity becomes large which increases sampling band and degrades SN ratio

Engineering Contradiction:

Improvenoise intensityVSAvoidSN ratio

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The invention applies local quality by making only the rising and falling portions of the gradient waveform convex upward, while keeping other portions conventional. This localized modification suppresses noise at critical transition points without excessively increasing maximum intensity, thus maintaining SN ratio while achieving noise reduction

Inventive Principle:

Principle #3Local quality

3Productivity

If conventional trapezoidal gradient waveforms are used, then imaging speed is maintained, but extremely loud noises of 80 to 100 dB are generated

Engineering Contradiction:

Improveimaging speedVSAvoidnoise intensity

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The invention changes the waveform parameter from trapezoidal to synthesized waveform with convex upward portions, which modifies the frequency spectrum to reduce noise-generating high-frequency components while maintaining the time integral value and application time, thus achieving noise reduction without sacrificing imaging speed

Inventive Principle:

Principle #35Parameter changes

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 reduces noise levels significantly, achieving a silencing effect comparable to sine waves while preserving the application time and intensity of traditional waveforms, thereby enhancing the design flexibility of MRI pulse sequences without increasing Specific Absorption Rate (SAR) or degrading Signal-to-Noise Ratio (SNR).

Implementation Method 1

application of the gradient magnetic field having a trapezoidal waveform is generally turned on and off at high speed, and therefore extremely loud noises of 80 to 100 dB are generated in the bore

Methodology Applied

Scientific EffectAcoustic noise generation from gradient magnetic field:

Implementation Method 2

at least one gradient magnetic field pulse included in the pulse sequence is a pulse having a waveform synthesized from two or more base waves shifting along the time axis direction, and the base waves have a smoothly changing waveform convex upward

Methodology Applied

Scientific EffectWaveform synthesis and noise suppression:

Data Source

PatentUS10048341B2Magnetic resonance imaging apparatus and method for calculating pulse sequence to be carried on magnetic resonance imaging apparatus

Publication Date: 2018.08.14 FUJIFILM CORP

AI summary

When imaging is performed by executing a pulse sequence on an MRI apparatus, silencing is realized with securing sufficient application amount of crusher without extending the application time thereof. In the pulse sequence carried by the MRI apparatus, at least one gradient magnetic field pulse included in the pulse sequence has a waveform synthesized from two or more base waves shifting along the time axis direction (synthesized waveform), and the base waves have a smoothly changing waveform convex upward. The pulse of the synthesized waveform is generated from one or more trapezoidal or triangular base pulses by a waveform conversion part of a computer of the MRI apparatus or an external computer.