MRI Image Reconstruction Using MaxGIRF Concomitant Field Correction

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Solution Overview

Problem

Spiral imaging in MRI faces challenges due to undesired spatially varying phase caused by concomitant fields, leading to image distortion and blurring, especially at high magnetic field strengths and off-center locations, where current solutions are either suboptimal or require expensive hardware.

Innovation Solution

The proposed MaxGIRF method uses an analytic concomitant field model incorporating high-order terms and gradient impulse response functions to correct distortion, estimating concomitant fields without the need for additional hardware, by predicting gradient waveforms and applying these corrections during image reconstruction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If spiral imaging is used to achieve high scan efficiency and motion artifact resistance, then productivity is improved, but image quality deteriorates due to spatially varying phase distortion from concomitant fields

Engineering Contradiction:

Improvescan efficiencyVSAvoidimage quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent pre-calculates and stores concomitant field values on a Cartesian grid before the actual imaging process. This preliminary computation allows the reconstruction algorithm to efficiently access and apply correction factors during spiral image reconstruction, resolving the phase distortion issue without adding computational burden during the time-critical reconstruction phase.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary Cartesian grid representation as a bridge between the ideal Cartesian field model and the actual spiral sampling data. By mapping concomitant field values onto this intermediate grid and using it to modulate the spiral k-space data during reconstruction, the method effectively corrects phase distortions while maintaining spiral imaging efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If high magnetic field strength is used to improve signal-to-noise ratio, then image quality is improved, but concomitant field distortion increases causing more severe image degradation

Engineering Contradiction:

Improveimage qualityVSAvoidconcomitant field distortion

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent acknowledges that concomitant fields produce predictable phase distortions that follow specific mathematical patterns. By explicitly modeling these distortion patterns and incorporating them into the reconstruction algorithm, the method converts the harmful phase errors into correctable signals, actually improving image quality at high field strengths where the distortions are most severe.

Inventive Principle:

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

3Device complexity

If conventional reconstruction methods are used to maintain simplicity, then device complexity is reduced, but image accuracy deteriorates due to uncorrected concomitant field effects

Engineering Contradiction:

Improvereconstruction algorithm simplicityVSAvoidimage accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent pre-computes and stores concomitant field correction factors in lookup tables before the actual imaging and reconstruction process. This preliminary preparation allows the reconstruction algorithm to simply retrieve and apply pre-calculated correction values without performing complex real-time calculations, maintaining algorithmic simplicity while significantly improving image accuracy.

Inventive Principle:

Principle #10Preliminary action

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 significantly reduces local blurring and artifacts in MRI images, improving image quality, especially at low-field strengths and off-center positions, while avoiding the need for costly NMR field probes, and enabling longer readouts and more flexible imaging.

Implementation Method 1

gradient coils produce magnetic field gradients

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

concomitant fields rotating in the counterclockwise direction in the rotating frame do not effectively nutate the spin but induce additional phase as the Bloch-Siegert effect

Methodology Applied

Scientific EffectBloch-Siegert effect:

Data Source

PatentUS20240164737A1Image reconstruction incorporating maxwell fields and gradient impulse response function distortion

Publication Date: 2024.05.23 UNIV OF SOUTHERN CALIFORNIA

AI summary

A system, computer readable medium, apparatus and/or method for magnetic resonance imaging (MRI) reconstruction that mitigates local blurring caused by static off-resonance and concomitant fields. The MRI reconstruction system may use phantom-based gradient impulse response function (GIRF) measurements and analytic expressions to predict the concomitant fields. GIRFs capture gradient delays, eddy current effects, and mechanically induced field oscillations. For each gradient axis, a MR system is perturbed with a set of input gradients. Gradients predicted with phantom-based GIRFs can better estimate concomitant fields than nominal gradients. A novel image reconstruction method incorporates higher-order Maxwell fields and GIRF trajectory corrections and may be treated as “invisible” field probes that require no special hardware but GIRFs measured with phantom-based methods and an analytic model of concomitant fields that depends on coil geometry and severity of gradient non-linearity.