Nyquist Ghost Correction in MRI via Cost Function Optimization

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Solution Overview

Problem

Existing MRI techniques struggle with Nyquist ghosting, particularly in diffusion-weighted imaging outside the head, due to limitations in ghost correction methods that are not effective in body imaging with insufficient fat suppression and increased B0 inhomogeneity.

Innovation Solution

A computerized method for self-correction of MRI images using a cost function that exploits cosine and sine modulation in the ghosted image component, allowing for referenceless Nyquist ghost correction, compatible with parallel imaging and multi-band/simultaneous multi-slice techniques.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional ghost correction methods (three-line navigator) are used, then brain imaging quality is improved, but body imaging fails due to insufficient fat suppression and increased B0 inhomogeneity

Engineering Contradiction:

Improveghost correction effectivenessVSAvoidapplicability to different imaging regions

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the fundamental parameters of ghost correction by transitioning from navigator-based methods to referenceless methods that operate directly on EPI data. This involves changing the mathematical approach from linear phase error modeling to cost function optimization that exploits cosine and sine modulation patterns, making the method adaptable to body imaging conditions with fat suppression challenges and B0 inhomogeneity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements self-service by using the EPI data itself for correction without requiring external navigator data. The referenceless methods use the inherent structure and modulation patterns within the acquired EPI data to correct Nyquist ghosts, eliminating the need for separate navigator acquisitions and making the correction self-contained and adaptable to various imaging scenarios

Inventive Principle:

Principle #25Self-service

2Loss of time

If referenceless methods are used, then additional navigator data acquisition is eliminated, but the method must handle low-rank structure constraints in multi-channel data

Engineering Contradiction:

Improveacquisition timeVSAvoiddata processing complexity

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The patent changes the processing approach by formulating ghost correction as a cost function optimization problem rather than simple phase correction. The method transforms the data into a form that exploits low-rank structure through Hankel matrix construction and SVD decomposition, changing the mathematical parameters from direct phase manipulation to iterative optimization with rank constraints

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes traditional mechanical navigator acquisition with a computational approach using cost function optimization. Instead of physically acquiring separate reference data, the system uses mathematical optimization on the acquired EPI data, replacing the mechanical data acquisition step with computational processing that achieves similar correction goals

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If multiple referenceless methods are combined, then ghost correction robustness is improved, but computational processing time increases

Engineering Contradiction:

Improveghost correction robustnessVSAvoidprocessing time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent merges multiple referenceless methods (ALOHA, entropy-based, low-rank Hankel matrix) into a unified framework. By combining these methods, the system leverages their complementary strengths to improve robustness across different imaging conditions, using the cost function to integrate results from multiple processing approaches

Inventive Principle:

Principle #5Merging (Combining)

4Manufacturing precision

If high b-values and high-resolution DWI are used, then image detail is improved, but Nyquist ghosting becomes more prominent

Engineering Contradiction:

Improveimage resolutionVSAvoidNyquist ghosting

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful effect of Nyquist ghosting into a useful signal by exploiting the characteristic cosine and sine modulation patterns that ghosts produce. Instead of treating ghosting as mere noise to be removed, the method uses these modulation patterns as the basis for the cost function, transforming the harmful artifact into information that guides the correction process

Inventive Principle:

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

Data Source

PatentUS11009577B2System and method for Nyquist ghost correction in medical imaging

Publication Date: 2021.05.18 REGENTS OF THE UNIVERSITY OF MINNESOTA

AI summary

A system and computerized method for generating magnetic resonance imaging (MRI) images is provided that includes accessing data acquired from a subject using an MRI system that includes Nyquist ghosts and processing the data using a cost function that exploits a cosine and sine modulation in a ghosted image component of the data. An image of the subject is produced from the data after processing the data using the cost function.