Quantification and compensation of eddy-current-induced magnetic-field gradients

Spees, William M.; Buhl, Niels; Sun, Peng; Ackerman, Joseph J. H.; Neil, Jeffrey J.; Garbow, Joel R.

doi:10.1016/j.jmr.2011.06.016

Cited by 46 publications

(43 citation statements)

References 33 publications

(60 reference statements)

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“…Additionally, mismatches in group delay between the RF and gradient subsystems can also lead to image distortion and/or deformation. To address eddy current effects, the actively shielded gradient coils and gradient waveform pre‐emphasis are used on the C3T system. However, eddy current effects can remain, causing k‐space trajectory deviations that are amplified during high‐spatial‐resolution acquisitions .…”

Section: Introductionmentioning

confidence: 99%

The effect of spiral trajectory correction on pseudo‐continuous arterial spin labeling with high‐performance gradients on a compact 3T scanner

Kang

Yarach

et al. 2019

Magnetic Resonance in Med

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Purpose To demonstrate the feasibility of pseudo‐continuous arterial‐spin–labeled (pCASL) imaging with 3D fast‐spin‐echo stack‐of‐spirals on a compact 3T scanner (C3T), to perform trajectory correction for eddy‐current–induced deviations in the spiral readout of pCASL imaging, and to assess the correction effect on perfusion‐related images with high‐performance gradients (80 mT/m, 700T/m/s) of the C3T. Methods To track eddy‐current–induced artifacts with Archimedean spiral readout, the spiral readout in pCASL imaging was performed with 5 different peak gradient slew rate (Smax) values ranging from 70 to 500 T/m/s. The trajectory for each Smax was measured using a dynamic field camera and applied in a density‐compensated gridding image reconstruction in addition to the nominal trajectory. The effect of the trajectory correction was assessed with perfusion‐weighted (ΔM) images and proton‐density–weighted images as well as cerebral blood flow (CBF) maps, obtained from 10 healthy volunteers. Results Blurring artifact on ΔM images was mitigated by the trajectory correction. CBF values on the left and right calcarine cortices showed no significant difference after correction. Also, the signal‐to‐noise ratio of ΔM images improved, on average, by 7.6% after correction (P < .001). The greatest improvement of 12.1% on ΔM images was achieved with a spiral readout using Smax of 300~400 T/m/s. Conclusion Eddy currents can cause spiral trajectory deviation, which leads to deformation of the CBF map even in cases of low value Smax. The trajectory correction for spiral‐readout–based pCASL produces more reliable results for perfusion imaging. These results suggest that pCASL is feasible on C3T with high‐performance gradients.

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Section: Introductionmentioning

confidence: 99%

The effect of spiral trajectory correction on pseudo‐continuous arterial spin labeling with high‐performance gradients on a compact 3T scanner

Kang

Yarach

et al. 2019

Magnetic Resonance in Med

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“…However, inhomogeneities in the magnetic field due to imperfect shimming, eddy currents and non-linear gradients will adversely affect the scanner’s spatial integrity resulting in reduced targeting accuracy and potentially reducing dose calculation accuracy (Spees et al 2011, Walker et al 2015). Additionally, patient-specific image distortion may also arise from spin populations characterized by different chemical shifts and magnetic susceptibility effects (Dietrich et al 2008, Stanescu et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Characterization of spatial distortion in a 0.35 T MRI-guided radiotherapy system

et al. 2017

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Spatial distortion results in image deformation that can degrade accurate targeting and dose calculations in MRI-guided adaptive radiotherapy. The authors present a comprehensive assessment of a 0.35 T MRI-guided radiotherapy system’s spatial distortion using two commercially-available phantoms with regularly spaced markers. Images of the spatial integrity phantoms were acquired using five clinical protocols on the MRI-guided radiotherapy machine with the radiotherapy gantry positioned at various angles. Software was developed to identify and localize all phantom markers using a template matching approach. Rotational and translational corrections were implemented to account for imperfect phantom alignment. Measurements were made to assess uncertainties arising from susceptibility artifacts, image noise, and phantom construction accuracy. For a clinical 3D imaging protocol with a 1.5 mm reconstructed slice thickness, 100% of spheres within a 50 mm radius of isocenter had a 3D deviation of 1 mm or less. Of the spheres within 100 mm of isocenter, 99.9% had a 3D deviation less than 1 mm. 94.8% and 100% of the spheres within 175 mm were found to be within 1 mm and 2 mm of the expected positions in 3D respectively. Maximum 3D distortions within 50 mm, 100 mm and 175 mm of isocenter were 0.76 mm, 1.15 mm and 1.88 mm respectively. Distortions present in images acquired using the real-time imaging sequence were less than 1 mm for 98.1% and 95.0% of the cylinders within 50 mm and 100 mm of isocenter. The corresponding maximum distortion in these regions was 1.10 mm and 1.67 mm. These results may be used to inform appropriate planning target volume (PTV) margins for 0.35 T MRI-guided radiotherapy. Observed levels of spatial distortion should be explicitly considered when using PTV margins of 3 mm or less or in the case of targets displaced from isocenter by more than 50 mm.

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“…These parameters can be determined by empirically measuring image distortions from gradient waveforms designed with a range of eddy current nulls, 50 measuring the eddy current-induced fields from the trailing edge of long gradient pulses with field cameras, 57 or by imaging the frequency shifts caused by eddy currents using specially designed phantoms. 57,58 In practice, the residual fields after gradient pre-emphasis may not have a well-defined set of time constants. The optimal approach in this scenario may be to enforce some tolerance over a range of eddy currents rather than nulling specific time constants.…”

Section: Discussionmentioning

confidence: 99%

Eddy current nulled constrained optimization of isotropic diffusion encoding gradient waveforms

Yang

McNab

2018

Magnetic Resonance in Med

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Purpose Isotropic diffusion encoding efficiently encodes additional microstructural information in combination with conventional linear diffusion encoding. However, the gradient‐intensive isotropic diffusion waveforms generate significant eddy currents, which cause image distortions. The purpose of this study is to present a method for designing isotropic diffusion encoding waveforms with intrinsic eddy current nulling. Methods Eddy current nulled gradient waveforms were designed using a constrained optimization waveform for a 3T GE Premier MRI system. Encoding waveforms were designed for a variety of eddy current null times and sequence timings to evaluate the achievable b‐value. Waveforms were also tested with both eddy current nulling and concomitant field compensation. Distortion reduction was tested in both phantoms and the in vivo human brain. Results The feasibility of isotropic diffusion encoding with intrinsic correction of eddy current distortion and signal bias from concomitant fields was demonstrated. The constrained optimization algorithm produced gradient waveforms with the specified eddy current null times. The reduction in the achievable diffusion weighting was dependent on the number of eddy current null times. A reduction in the eddy current–induced image distortions was observed in both phantoms and in vivo human subjects. Conclusion The proposed framework allows the design of isotropic diffusion‐encoding sequences with reduced image distortion.

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Quantification and compensation of eddy-current-induced magnetic-field gradients

Cited by 46 publications

References 33 publications

The effect of spiral trajectory correction on pseudo‐continuous arterial spin labeling with high‐performance gradients on a compact 3T scanner

The effect of spiral trajectory correction on pseudo‐continuous arterial spin labeling with high‐performance gradients on a compact 3T scanner

Characterization of spatial distortion in a 0.35 T MRI-guided radiotherapy system

Eddy current nulled constrained optimization of isotropic diffusion encoding gradient waveforms

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