MRI Gradient Waveform Design for K-Space Trajectory Accuracy

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Solution Overview

Problem

Magnetic resonance imaging (MRI) techniques face challenges in achieving high-quality images due to artifacts caused by k-space trajectories deviating from intended paths, particularly with spiral trajectories, as existing methods fail to adequately account for the limited frequency response of gradient hardware.

Innovation Solution

Incorporating a frequency limit F into the design of the time dependence function for the gradient waveform, ensuring it only contains frequency components that can be generated by the MRI system, thereby aligning the actual k-space trajectory with the intended one and minimizing artifacts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a spiral k-space trajectory is used to accelerate scanning, then productivity is improved, but manufacturing precision deteriorates due to trajectory deviations and artifacts

Engineering Contradiction:

Improvescanning speedVSAvoidtrajectory accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies parameter changes by modifying the gradient waveform parameters (amplitude, frequency, phase) to compensate for hardware limitations. Specifically, the gradient waveform is designed with time-varying parameters that account for the frequency response roll-off, ensuring the actual trajectory matches the intended spiral path while maintaining fast scanning speeds

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements preliminary action by pre-calculating and pre-distorting the gradient waveform parameters before application. The gradient waveform is designed in advance with built-in compensation for the system's frequency response characteristics, so that when applied, it produces the desired trajectory despite hardware limitations

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If gradient waveform with high frequency components is applied to achieve precise trajectory, then manufacturing precision is improved, but reliability deteriorates due to hardware frequency response limitations

Engineering Contradiction:

Improvetrajectory accuracyVSAvoidhardware compatibility

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent applies feedback by incorporating the known frequency response characteristics of the gradient hardware into the waveform design process. The gradient waveform parameters are adjusted based on feedback from the system's measured or specified frequency response, ensuring that the waveform remains within the reliable operating range of the hardware while achieving the desired trajectory

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent implements dynamics by using time-varying gradient waveforms with dynamically adjusted parameters. The gradient amplitude, frequency, and phase are continuously modulated during the scan to stay within the hardware's frequency response capabilities while maintaining trajectory accuracy, rather than using static or overly simplistic waveforms

Inventive Principle:

Principle #15Dynamics

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 ensures that the true k-space trajectory closely follows the intended path, reducing artifacts and simplifying image reconstruction, while adhering to gradient hardware limitations, thus improving MRI image quality.

Implementation Method 1

Magnetic resonance imaging (MRI) is a powerful, non-invasive tool for obtaining spatially resolved information of objects

Methodology Applied

Scientific EffectLarmor precession:

Implementation Method 2

Typically, frequency encoding and/or phase encoding procedures are applied by means of field gradients

Methodology Applied

Scientific EffectFrequency encoding:

Implementation Method 3

Typically, frequency encoding and/or phase encoding procedures are applied by means of field gradients

Methodology Applied

Scientific EffectPhase encoding:

Implementation Method 4

the time dependence function is designed such that its resulting (target) gradient waveform gm(t) varies in a fashion only containing frequency components that may be generated with the given gradient hardware

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentEP2372383B1Design of a gradient waveform for a k-space trajectory with an upper frequency limit due to MRI gradient hardware

Publication Date: 2015.12.16 BRUKER BIOSPIN MRI GMBH

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AI summary

A method for designing the time dependent function km(t) for a given k-space trajectory km, where m stands for one or multiple of the spatial dimension indices x, y, or z, of a magnetic resonance imaging (=MRI) experiment carried out on an MRI system, wherein the trajectory km is generated by applying a time varying waveform gm(t) of a gradient magnetic field, the method taking into account - the gradient magnitude limit G and - the gradient slew rate limit S of the MRI system, is characterized in that the method further takes into account a given frequency limit F in such a way that the gradient waveform gm(t) does not contain frequency components above the frequency limit F which is characteristic for the gradient hardware of the MRI system. The invention provides a method for designing a time dependence function for a given k-space trajectory, which allows obtaining better quality MRI images.