Characterization and correction of time‐varying eddy currents for diffusion MRI

• Published in: Magnetic resonance in medicine Vol. 87; no. 5; pp. 2209 - 2223
• Main Authors: Valsamis, Jake J., Dubovan, Paul I., Baron, Corey A.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.05.2022
• Subjects: Algorithms; Blurring; brain; Brain - diagnostic imaging; Decay; Diffusion; Diffusion Magnetic Resonance Imaging - methods; diffusion MRI; Echo-Planar Imaging - methods; Eddy current testing; Eddy currents; Error correction; field monitoring; Image acquisition; Image Processing, Computer-Assisted - methods; Image quality; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Medical imaging; Monitoring; OGSE; Polarity; Reconstruction; Retrospective Studies; Time constant; validation; diffusion MRI; eddy currents; brain; field monitoring; OGSE; validation
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.29124

Purpose To develop and test a method for reducing artifacts due to time‐varying eddy currents in oscillating gradient spin‐echo (OGSE) diffusion images. Methods An in‐house algorithm (TVEDDY), that for the first time retrospectively models eddy current decay, was tested on pulsed gradient spin echo and OGSE brain images acquired at 7 T. Image pairs were acquired using opposite polarity diffusion gradients. A three‐parameter exponential decay model (two amplitudes and a time constant) was used to characterize and correct eddy current distortions by minimizing the intensity difference between image pairs. Correction performance was compared with conventional correction methods by evaluating the mean squared error (MSE) between diffusion‐weighted images acquired with opposite polarity diffusion gradients. As a ground‐truth comparison, images were corrected using field dynamics up to third order in space, measured using a field monitoring system. Results Time‐varying eddy currents were observed for OGSE, which introduced blurring that was not reduced using the traditional approach but was diminished considerably with TVEDDY and field monitoring–informed model‐based reconstruction. No MSE difference was observed between the conventional approach and TVEDDY for pulsed gradient spin echo, but for OGSE TVEDDY resulted in significantly lower MSE than the conventional approach. The field‐monitoring reconstruction had the lowest MSE for both pulsed gradient spin echo and OGSE. Conclusion This work establishes that it is possible to estimate time‐varying eddy currents from the actual diffusion data, which provides substantial image‐quality improvements for gradient‐intensive diffusion MRI acquisitions like OGSE.