Arbitrary magnetic field gradient waveform correction using an impulse response based pre-equalization technique

Goora, Frédéric G.; Colpitts, Bruce G.; Balcom, Bruce J.

doi:10.1016/j.jmr.2013.11.003

Cited by 35 publications

(31 citation statements)

References 39 publications

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“…The gradient impulse response function (GIRF) has been used to predict the true k-space trajectories from the nominal trajectories in post-processing (10–12), and to predetermine optimal input waveforms (13). …”

Section: Introductionmentioning

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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Section: Introductionmentioning

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

View full text Add to dashboard Cite

show abstract

“…Using measurements of the gradient, the shape of the gradient is corrected using a method known as gradient pre-equalization [22]. The method is outlined in Fig.…”

Section: Implementation Of Slice Selectionmentioning

confidence: 99%

“…Deconvolution is prone to amplifying noise as it involves division in the frequency domain. To overcome this, Goora et al [22] model their measured gradient using a polynomial. Here, we use a Gaussian filter, with a standard deviation of 200,000 Hz, in the Fourier domain to suppress the noise.…”

Section: Implementation Of Slice Selectionmentioning

confidence: 99%

“…UTE is sensitive to the shape of the slice selection gradient, therefore it is desirable to ensure the gradient shape is accurate. A recently published technique by Goora et al [22] introduces the idea of gradient pre-equalization as a technique to correct for the induced errors in gradient shape when using a short ramp. Their approach is applicable on almost any hardware platform and therefore is appealing for UTE imaging applications in material science and chemical engineering.…”

mentioning

confidence: 99%

“…Experimental measurements are then used to demonstrate the implementation of accurate slice selection using UTE. In order to ensure accurate slice selection, the shape of the slice selection gradient was optimized by introducing the gradient pre-equalization of Goora et al [22]. To reduce the acquisition time without introducing artifacts CS is used for image reconstruction.…”

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confidence: 99%

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Ultrashort echo time (UTE) imaging using gradient pre-equalization and compressed sensing

Fabich

Benning

Sederman

et al. 2014

Journal of Magnetic Resonance

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Ultrashort echo time (UTE) imaging is a well-known technique used in medical MRI, however, the implementation of the sequence remains non-trivial. This paper introduces UTE for non-medical applications and outlines a method for the implementation of UTE to enable accurate slice selection and short acquisition times. Slice selection in UTE requires fast, accurate switching of the gradient and r.f. pulses. Here a gradient "pre-equalization" technique is used to optimize the gradient switching and achieve an effective echo time of 10μs. In order to minimize the echo time, k-space is sampled radially. A compressed sensing approach is used to minimize the total acquisition time. Using the corrections for slice selection and acquisition along with novel image reconstruction techniques, UTE is shown to be a viable method to study samples of cork and rubber with a shorter signal lifetime than can typically be measured. Further, the compressed sensing image reconstruction algorithm is shown to provide accurate images of the samples with as little as 12.5% of the full k-space data set, potentially permitting real time imaging of short T2(*) materials.

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Accuracy of the Magnetic Field Gradient Waveform Monitor Technique and Consequent Accuracy of Pre‐Equalized Gradient Waveform

Goora

Balcom

2016

Concepts Magn Reson

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The magnetic field gradient waveform monitor (MFGM) technique permits characterization of the temporal evolution of magnetic field gradients in magnetic resonance (MR) instruments (MRIs). Knowledge of the gradient waveform performance permits the development of further techniques, such as gradient waveform pre‐equalization, that correct and optimize gradient waveform distortions due to eddy currents induced during the application of switched magnetic fields and other system limitations. The accuracy of the MFGM technique is important since the overall uncertainty of the gradient waveform measurement will propagate into an uncertainty in corrected gradient waveforms impacting the precision of the resulting MR/MRI measurements. The accuracy of MFGM is investigated through a treatment of the noise present in a MRI. A noisy receiver model provides the basis for characterization of the noise and permits examination of the overall impact of noise on the phase accumulated in a pure‐phase encoded MR signal. Ultimately, a relationship between the signal‐to‐noise ratio of a measurement and the corresponding MFGM uncertainty is developed. The theoretical development is supported through simulation in conjunction with experimental results. The propagation of uncertainties to gradient waveform pre‐equalization is also discussed.

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Arbitrary magnetic field gradient waveform correction using an impulse response based pre-equalization technique

Cited by 35 publications

References 39 publications

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

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

Ultrashort echo time (UTE) imaging using gradient pre-equalization and compressed sensing

Accuracy of the Magnetic Field Gradient Waveform Monitor Technique and Consequent Accuracy of Pre‐Equalized Gradient Waveform

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