Monitoring, analysis, and correction of magnetic field fluctuations in echo planar imaging time series

Kasper, Lars; Bollmann, Saskia; Vannesjo, S. Johanna; Gross, Simon; Haeberlin, Maximilian; Dietrich, Benjamin E.; Pruessmann, Klaas P.

doi:10.1002/mrm.25407

Cited by 36 publications

(49 citation statements)

References 27 publications

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“…In the present work, field dynamics were recorded with NMR probes, which is convenient in that it can be performed concurrently with actual imaging and will capture potential system drifts and other transient effects. In previous studies, magnet drift and heating of gradient coils have been identified as relevant system changes, giving rise to image variation up to several percent in EPI . Differences between trajectory prediction based on impulse response and concurrent trajectory recording were also reported in Ref , resulting in RMS image differences of approximately 2% for single‐shot spiral imaging.…”

Section: Discussionmentioning

confidence: 91%

Single‐shot spiral imaging at 7 T

Engel

Kasper

Barmet

et al. 2018

Magnetic Resonance in Med

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Section: Discussionmentioning

confidence: 91%

Single‐shot spiral imaging at 7 T

Engel

Kasper

Barmet

et al. 2018

Magnetic Resonance in Med

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“…There are other methods to achieve real-time distortion correction. In sites with access to the equipment, real-time field monitoring could be employed for trajectory calculation (21). Alternatively, The GIRF could be used to calculate the input waveform needed to produce the ideal waveform in the scanner bore, and thus, corrected waveforms could be prescribed in the pulse sequence (13).…”

Section: Discussionmentioning

confidence: 99%

Real‐time distortion correction of spiral and echo planar images using the gradient system impulse response function

Campbell-Washburn

Xue

Lederman

et al. 2015

Magnetic Resonance in Med

115

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Purpose MRI-guided interventions demand high frame-rate imaging, making fast imaging techniques such as spiral imaging and echo planar imaging (EPI) appealing. In this study, we implemented a real-time distortion correction framework to enable the use of these fast acquisitions for interventional MRI. Methods Distortions caused by gradient waveform inaccuracies were corrected using the gradient impulse response function (GIRF), which was measured by standard equipment and saved as a calibration file on the host computer. This file was used at runtime to calculate the predicted k-space trajectories for image reconstruction. Additionally, the off-resonance reconstruction frequency was modified in real-time to interactively de-blur spiral images. Results Real-time distortion correction for arbitrary image orientations was achieved in phantoms and healthy human volunteers. The GIRF predicted k-space trajectories matched measured k-space trajectories closely for spiral imaging. Spiral and EPI image distortion was visibly improved using the GIRF predicted trajectories. The GIRF calibration file showed no systematic drift in 4 months and was demonstrated to correct distortions after 30 minutes of continuous scanning despite gradient heating. Interactive off-resonance reconstruction was used to sharpen anatomical boundaries during continuous imaging. Conclusions This real-time distortion correction framework will enable the use of these high frame-rate imaging methods for MRI-guided interventions.

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“…The variance component arriving from most of these sources can be reduced in principle. For example, using magnetic field probes (De Zanche et al, 2008) the effects of scanner instability or breathing on the quality of EPI images can be reduced (Kasper et al, 2014). Other possibilities are prospective motion correction, that has been shown to provide a benefit for collecting fMRI time-series data (Maclaren et al, 2013; Haeberlin et al, 2014; Todd et al, 2015), or improved shimming, that would reduce individualized susceptibility-induced distortions and drop-out artifacts.…”

Section: Discussionmentioning

confidence: 99%

Investigating the Group-Level Impact of Advanced Dual-Echo fMRI Combinations

et al. 2016

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Multi-echo fMRI data acquisition has been widely investigated and suggested to optimize sensitivity for detecting the BOLD signal. Several methods have also been proposed for the combination of data with different echo times. The aim of the present study was to investigate whether these advanced echo combination methods provide advantages over the simple averaging of echoes when state-of-the-art group-level random-effect analyses are performed. Both resting-state and task-based dual-echo fMRI data were collected from 27 healthy adult individuals (14 male, mean age = 25.75 years) using standard echo-planar acquisition methods at 3T. Both resting-state and task-based data were subjected to a standard image pre-processing pipeline. Subsequently the two echoes were combined as a weighted average, using four different strategies for calculating the weights: (1) simple arithmetic averaging, (2) BOLD sensitivity weighting, (3) temporal-signal-to-noise ratio weighting and (4) temporal BOLD sensitivity weighting. Our results clearly show that the simple averaging of data with the different echoes is sufficient. Advanced echo combination methods may provide advantages on a single-subject level but when considering random-effects group level statistics they provide no benefit regarding sensitivity (i.e., group-level t-values) compared to the simple echo-averaging approach. One possible reason for the lack of clear advantages may be that apart from increasing the average BOLD sensitivity at the single-subject level, the advanced weighted averaging methods also inflate the inter-subject variance. As the echo combination methods provide very similar results, the recommendation is to choose between them depending on the availability of time for collecting additional resting-state data or whether subject-level or group-level analyses are planned.

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Monitoring, analysis, and correction of magnetic field fluctuations in echo planar imaging time series

Abstract: Concurrent magnetic field monitoring holds the potential to improve the net sensitivity of fMRI by reducing signal fluctuations unrelated to brain activity.

Cited by 36 publications

References 27 publications

Single‐shot spiral imaging at 7 T

Single‐shot spiral imaging at 7 T

Real‐time distortion correction of spiral and echo planar images using the gradient system impulse response function

Investigating the Group-Level Impact of Advanced Dual-Echo fMRI Combinations

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