On the signal‐to‐noise ratio benefit of spiral acquisition in diffusion MRI

Lee, Yoojin; Wilm, Bertram J.; Brunner, David O.; Gross, Simon; Schmid, Thomas; Nagy, Zoltán; Pruessmann, Klaas P.

doi:10.1002/mrm.28554

Cited by 35 publications

(52 citation statements)

References 55 publications

(114 reference statements)

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“…At high resolution, the benefit of TE reduction using echo-train shifting over the conventional acquisition is more prominent, since the long echo train before the spin-echo with large echo spacing will lead to long TE in ss-EPI. The benefit of minimizing the TE has also been studied in many previous works, such as center-out spiral (49,50), and center-out EPI (51). One challenge of using a center-out trajectory in conventional single-shot acquisition is that the fast T 2 * decay would lead to more image blurring that needs to be corrected.…”

Section: Discussionmentioning

confidence: 99%

SNR-efficient distortion-free diffusion relaxometry imaging using ACcelerated Echo-train shifted EPTI (ACE-EPTI)

Dong

Wang

Wald

et al. 2021

Preprint

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Purpose: To develop an efficient acquisition technique for distortion-free diffusion MRI and diffusion-relaxometry. Methods: A new ACcelerated Echo-train shifted Echo-Planar Time-resolved Imaging (ACE-EPTI) technique is developed to achieve high-SNR, distortion- and blurring-free diffusion and diffusion-relaxometry imaging. ACE-EPTI employs a newly designed variable density spatiotemporal encoding with self-navigation capability, that allows submillimeter in-plane resolution using only 3-shot. Moreover, an echo-train-shifted acquisition is developed to achieve minimal TE, together with an SNR-optimal readout length, leading to ~30% improvement in SNR efficiency over single-shot EPI. To recover the highly accelerated data with high image quality, a tailored subspace image reconstruction framework is developed, that corrects for odd/even-echo phase difference, shot-to-shot phase variation, and the B0 field changes due to field drift and eddy currents across different dynamics. After the phase-corrected subspace reconstruction, artifacts-free high-SNR diffusion images at multiple TEs are obtained with varying T2* weighting. Results: Simulation, phantom and in-vivo experiments were performed, which validated the 3-shot spatiotemporal encoding provides accurate reconstruction at submillimeter resolution. The use of echo-train shifting and optimized readout length improves the SNR-efficiency by 27-36% over single-shot EPI. The reconstructed multi-TE diffusion images were demonstrated to be free from distortion (susceptibility and eddy currents) and phase/field variation induced artifacts. These improvements of ACE-EPTI enable improved diffusion tensor imaging and rich multi-TE information for diffusion-relaxometry analysis. Conclusion: ACE-EPTI was demonstrated to be an efficient and powerful technique for high-resolution diffusion imaging and diffusion-relaxometry, which provides high SNR, distortion- and blurring-free, and time-resolved multi-echo images by a fast 3-shot acquisition.

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Section: Discussionmentioning

confidence: 99%

SNR-efficient distortion-free diffusion relaxometry imaging using ACcelerated Echo-train shifted EPTI (ACE-EPTI)

Dong

Wang

Wald

et al. 2021

Preprint

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“…To enable single-shot imaging for maximum acquisition efficiency, we also relied on the coil sensitivity profiles for spatial encoding, i.e., parallel imaging. Spiral trajectories are particularly suited for this form of acceleration, because they possess favorable behavior in terms of spatial noise amplification by the coil geometry factor, allowing for higher k-space undersampling (Larkman, 2007; Lee et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

Advances in Spiral fMRI: A High-resolution Study with Single-shot Acquisition

Kasper

Engel

Heinzle

et al. 2019

Preprint

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Spiral fMRI has been put forward as a viable alternative to rectilinear echo-planar imaging, in particular due to its enhanced average k-space speed and thus high acquisition efficiency. This renders spirals attractive for contemporary fMRI applications that require high spatiotemporal resolution, such as laminar or columnar fMRI. However, in practice, spiral fMRI is typically hampered by its reduced robustness and ensuing blurring artifacts, which arise from unaccounted imperfections in both static and dynamic magnetic fields.Recently, these limitations have been overcome by the concerted application of an expanded signal model factoring in such field imperfections, and its corresponding inversion by iterative image reconstruction. In the challenging ultra-high field environment of 7 Tesla, where field inhomogeneity effects are aggravated, both multi-shot and single-shot 2D spiral imaging at sub-millimeter resolution was demonstrated with high depiction quality and anatomical congruency.In this work, we further these advances towards a time series application of spiral readouts, namely, single-shot spiral BOLD fMRI at 0.8mm in-plane resolution. We report that spiral fMRI at 7T is feasible, delivering both competitive image quality and BOLD sensitivity, with a spatial specificity of the activation maps that is not compromised by artifactual blurring. Furthermore, we show the versatility of the approach with a combined in/out spiral readout at a more typical resolution (1.5 mm), where the high acquisition efficiency allows to acquire two images per shot for improved sensitivity by echo combination. Advances in Spiral fMRI 3/42 Advances in Spiral fMRI 5/42

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“…Overall, by integrating the field camera into the coil, scanning workflow is greatly improved and the design architecture now facilitates subject-specific field corrections caused by motionwhich can be more prominent for longer acquisition protocols 33 . (c) Field dynamics measured by probes while on the scaffold, and corrected with a third-order fit, were used as a reference.…”

Section: Field-camera Performancementioning

confidence: 99%

Section: Field-camera Performancementioning

confidence: 99%

“…Concurrent field monitoring has been demonstrated to produce improvements in functional 28,29 and anatomical 30 imaging, with spiral encoding being particularly well-served by this correction technique due to its sensitivity to non-idealities in the gradient trajectory 29 . Diffusion-weighted imaging 31,32 can achieve substantial SNR gains by leveraging spiral encoding 33 , making it an ideal application of concurrent field monitoring 34 . Diffusion-weighted imaging has benefited from recent technological advances 35 , as it relies on high SNR and gradient strengths (b-values) to probe differences in molecular motion caused by the local anatomy.…”

Section: Introductionmentioning

confidence: 99%

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Integration of a radiofrequency coil and commercial field camera for ultra-high-field MRI

Gilbert

Dubovan

Gati

et al. 2021

Preprint

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Purpose: To develop an RF coil with an integrated commercial field camera for ultra-high field (7 T) neuroimaging. The RF coil will operate within a head-only gradient coil and be subject to the corresponding design constraints. The RF coil can thereafter be used for subject-specific correction of k-space trajectories-notably in gradient-sensitive sequences such as single-shot spiral imaging. Methods: The transmit and receive performance was evaluated before and after the integration of field probes, while field probes were evaluated when in an optimal configuration external to the coil and after their integration. Diffusion-weighted EPI and single-shot spiral acquisitions were employed to evaluate the efficacy of correcting higher order field perturbations and the consequent effect on image quality. Results: Field probes had a negligible effect on RF-coil performance, including the transmit efficiency, transmit uniformity, and mean SNR over the brain. Modest reductions in field-probe signal lifetimes were observed, caused primarily by non-idealities in the gradient and shim fields of the head-only gradient coil at the probe positions. The field monitoring system could correct up to second-order field perturbations in single-shot spiral imaging. Conclusion: The integrated RF coil and field camera was capable of concurrent field monitoring within a 7T head-only scanner and facilitated the subsequent correction of k-space trajectories during spiral imaging.

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On the signal‐to‐noise ratio benefit of spiral acquisition in diffusion MRI

Cited by 35 publications

References 55 publications

SNR-efficient distortion-free diffusion relaxometry imaging using ACcelerated Echo-train shifted EPTI (ACE-EPTI)

SNR-efficient distortion-free diffusion relaxometry imaging using ACcelerated Echo-train shifted EPTI (ACE-EPTI)

Advances in Spiral fMRI: A High-resolution Study with Single-shot Acquisition

Integration of a radiofrequency coil and commercial field camera for ultra-high-field MRI

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