Minimization of Eddy Current Artifacts in Sequences with Periodic Dynamics

TL;DR

This paper introduces a novel reordering method for k-space sampling in periodic MRI sequences, significantly reducing eddy current artifacts by formulating the problem as a traveling salesman problem and applying simulated annealing.

Contribution

It presents a new reordering algorithm based on discrete optimization to minimize eddy current artifacts in balanced gradient MRI sequences, leveraging periodicity for improved sampling.

Findings

Substantial reduction of artifacts in reconstructed images.

Slightly better performance of the all-jumps-minimized variant.

Effective artifact reduction without changing overall k-space trajectory.

Abstract

Purpose: To minimize eddy current artifacts in periodic pulse sequences with balanced gradient moments as, e.g., used for quantitative MRI. Theory and Methods: Eddy current artifacts in balanced sequences result from large jumps in k-space. In quantitative MRI, one often samples some spin dynamics repeatedly while acquiring different parts of k-space. We swap individual k-space lines between different repetitions in order to minimize jumps in temporal succession without changing the overall trajectory. This reordering can be formulated as a traveling salesman problem and we tackle the discrete optimization with a simulated annealing algorithm. Results: Compared to the default ordering, we observe a substantial reduction of artifacts in the reconstructed images and the derived quantitative parameter maps. Comparing two variants of our algorithm, one that resembles the pairing approach originally proposed by Bieri et al., and one that minimizes all k-space jumps equally, we observe slightly lower artifact levels in the latter. Conclusion: The proposed reordering scheme effectively reduces eddy current artifacts in sequences with balanced gradient moments. In contrast to previous approaches, we capitalize on the periodicity of the sampled signal dynamics, enabling both efficient k-space sampling and minimizing artifacts caused by eddy currents.