Asymmetric Gradient Waveform Minimizes Concomitant Field Artefacts
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Solution Overview
Problem
Conventional diffusion-weighted magnetic resonance imaging (dMRI) techniques face challenges with concomitant magnetic field effects, leading to signal attenuation and image artefacts, particularly due to residual gradient moments, which are not adequately addressed by existing correction methods that require position-dependent gradients and are limited to central imaging regions.
Innovation Solution
Designing time-dependent magnetic field gradients that are asymmetric with respect to a refocusing pulse, minimizing the effects of concomitant fields by optimizing waveform components to achieve zero integral of GTG before and after the pulse, and ensuring the Maxwell index is within a threshold, thereby reducing artefacts across all imaging regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional pulsed gradient waveforms are used for diffusion encoding, then the imaging sequence is simple to implement, but concomitant magnetic field effects cause signal attenuation and image artefacts
Solution Approach 1:
The patent applies asymmetry by designing gradient waveforms that are asymmetric with respect to the refocusing pulse. Specifically, the gradient waveform has different amplitudes or durations before and after the refocusing pulse, which creates a net zero moment for the concomitant fields while maintaining the desired diffusion encoding effect. This asymmetric design eliminates the harmful concomitant field artefacts without requiring complex position-dependent corrections.
2Productivity
If gradient waveforms are optimized for specific b-tensor shapes, then encoding efficiency is improved, but the solution becomes limited to specific orientations and requires position-dependent corrections
Solution Approach 1:
The patent achieves universality by creating gradient waveforms that simultaneously provide efficient diffusion encoding for multiple b-tensor shapes and orientations. The asymmetric waveform design with zero net moment is orientation-independent, meaning it effectively suppresses concomitant field effects regardless of the imaging orientation or b-tensor configuration. This universal solution eliminates the need for position-dependent corrections and allows the same waveform to be used across different imaging scenarios.
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 minimizes concomitant field artefacts regardless of b-tensor shape or orientation, maintaining high efficacy and allowing for broader imaging strategies like simultaneous multi-slice techniques, without the need for position-dependent corrections, thus enhancing signal quality and reducing artefacts in both central and peripheral regions.
Implementation Method 1
generating by a gradient coil of a magnetic resonance imaging scanner a time-dependent magnetic field gradient G(t)=[Gx(t)Gy(t)Gz(t)]T
Implementation Method 2
an attenuation factor due to T2* relaxation is one
Data Source
AI summary
Disclosed is a method for generating a time-dependent magnetic field gradient in diffusion weighted magnetic resonance imaging G(t)=[Gx(t)Gy(t)Gz(t)]T, which is asymmetric in time with respect to a refocusing pulse, by meeting one or more of the requirements: A=∫0TEh(t)G(t)G(t)Tdt is zero, where TE is an echo time and h(t) is a function of time which is positive during an interval prior to the refocusing pulse and negative during a time interval after the refocusing pulse); minimize A or m=(Tr[AA])1/2 where A=∫P1G(t)G(t)Tdt−∫P2G(t)G(t)Tdt where P1 and P2 represent time intervals prior to and subsequent to the refocusing pulse; m is smaller than a threshold value. an attenuation factorAFp=exp(-tT2*)due to T2* relaxation is one. Signal attenuation due to concomitant field gradients, regardless of the shape or orientation of the diffusion encoding b-tensor and the location of signal is hereby minimized.