Diffusion dispersion imaging: Mapping oscillating gradient spin‐echo frequency dependence in the human brain

Arbabi, Aidin; Kai, Jason; Khan, Ali R.; Baron, Corey A.

doi:10.1002/mrm.28083

Cited by 43 publications

(82 citation statements)

References 38 publications

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“…Linear trends of the diffusivities and FA were also reported in the only other OGSE study of the in vivo human brain using a high-performance gradient system, 13 and general positive trends of these parameters were observed in several other in vivo human OGSE studies using standard gradient strengths. 4,5,23 Moreover, the b-value employed in this work surpasses those used previously by a factor of at least 2, permitting diffusion tensor computation with less bias by microcirculatory flow. 22,25…”

Section: In Vivo Brain Imagingmentioning

confidence: 86%

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Improved gradient waveforms for oscillating gradient spin‐echo (OGSE) diffusion tensor imaging

2020

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The dependence of the diffusion tensor on frequency is of great interest in studies of tissue microstructure because it reveals restrictions to the Brownian motion of water molecules caused by cell membranes. Oscillating gradient spin‐echo (OGSE) sequences can sample this dependence with gradient shapes for which the power spectrum of the zeroth moment is focused at a target frequency. In order to maintain the total spectral power (ie the b‐value), oscillating gradient amplitudes must grow with the frequency squared. For this reason, OGSE applications on clinical MRI scanners are limited to low frequencies, for which it is difficult to obtain a narrow frequency bandwidth of the gradient moment in a useful echo time. In particular, the commonly used pair of single‐period trapezoidal‐cosine pulses separated by a half‐period produces significant side lobes away from the target frequency. To mitigate this effect, improved OGSE waveforms are proposed, which reduce the gap between the two gradient pulses to the minimum duration required for the refocusing RF pulse. Additionally, a slight deviation from the periodicity of the waveforms is proposed in order to permit using the maximum slew rate of the gradient system for all lobes of trapezoidal waveforms while maintaining advantageous spectral properties, which is not the case for the currently used OGSE sequences. Numerical calculations validate these changes, showing that both modifications significantly narrow the gradient moment power spectrum and increase the contribution of its main lobe to the b‐value, thus improving the specificity of the measurement. The utility of the new shapes is demonstrated by diffusion tensor measurements of human white matter in vivo over the range of 30‐75 Hz with a b‐value of nearly 1000 s/mm2, using a high‐performance gradient insert. However, the improvement should increase the sampling precision of OGSE experiments for all gradient systems.

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Section: In Vivo Brain Imagingmentioning

confidence: 86%

“…We therefore conclude that computations of diffusion tensors and the related metrics cannot have been significantly affected by such errors, especially because the deviations are small with respect to the magnitude of expected diffusivity and anisotropy changes in vivo with increasing frequency. 5,23…”

Section: Gradient Sequence Simulationsmentioning

confidence: 99%

Improved gradient waveforms for oscillating gradient spin‐echo (OGSE) diffusion tensor imaging

2020

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“…

D_{\infty}

is defined as long range diffusivity and is the intercept. The slope

d D / d f

has also been defined as the diffusion dispersion rate (DDR) and is related to

l_{c}

by DDR

\approx 0.987 l_{c}^{2}

.…”

Section: Methodsmentioning

confidence: 99%

Oscillating diffusion‐encoding with a high gradient‐amplitude and high slew‐rate head‐only gradient for human brain imaging

Tan

Shih

Mitra

et al. 2020

Magnetic Resonance in Med

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Purpose:We investigate the importance of high gradient-amplitude and high slew-rate on oscillating gradient spin echo (OGSE) diffusion imaging for human brain imaging and evaluate human brain imaging with OGSE on the MAGNUS head-gradient insert (200 mT/m amplitude and 500 T/m/s slew rate). Methods: Simulations with cosine-modulated and trapezoidal-cosine OGSE at various gradient amplitudes and slew rates were performed. Six healthy subjects were imaged with the MAGNUS gradient at 3T with OGSE at frequencies up to 100 Hz and b = 450 s/mm 2 . Comparisons were made against standard pulsed gradient spin echo (PGSE) diffusion in vivo and in an isotropic diffusion phantom. Results: Simulations show that to achieve high frequency and b-value simultaneously for OGSE, high gradient amplitude, high slew rates, and high peripheral nerve stimulation limits are required. A strong linear trend for increased diffusivity (mean: 8-19%, radial: 9-27%, parallel: 8-15%) was observed in normal white matter with OGSE (20 Hz to 100 Hz) as compared to PGSE. Linear fitting to frequency provided excellent correlation, and using a short-range disorder model provided radial longterm diffusivities of D ∞,MD = 911 ± 72 µm 2 /s, D ∞,PD = 1519 ± 164 µm 2 /s, and D ∞,RD = 640 ± 111 µm 2 /s and correlation lengths of l c,MD = 0.802 ± 0.156 µm, l c,PD = 0.837 ± 0.172 µm, and l c,RD = 0.780 ± 0.174 µm. Diffusivity changes with OGSE frequency were negligible in the phantom, as expected. Conclusion: The high gradient amplitude, high slew rate, and high peripheral nerve stimulation thresholds of the MAGNUS head-gradient enables OGSE acquisition for in vivo human brain imaging. K E Y W O R D S diffusion imaging, head-gradient, microstructure | 951 TAN eT Al.

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“…In particular, the ratio of the duration of the phase‐encoding period

δ

with respect to the diffusion time Δ may be chosen more flexibly, which may be relevant in several advanced diffusion model such as q‐space 34 and multidimensional diffusion encoding 35 . Moreover, DWI with oscillating gradients 36 may also profit from the newly available gradient performance. Generally, the enabled increase in signal yield benefits the derivation of quantitative diffusion values 37 .…”

Section: Discussionmentioning

confidence: 99%

Minimizing the echo time in diffusion imaging using spiral readouts and a head gradient system

Wilm

Hennel

Roesler

et al. 2020

Magnetic Resonance in Med

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Purpose Diffusion weighted imaging (DWI) is commonly limited by low signal‐to‐noise ratio (SNR) as well as motion artifacts. To address this limitation, a method that allows to maximize the achievable signal yield and increase the resolution in motion robust single‐shot DWI is presented. Methods DWI was performed on a 3T scanner equipped with a recently developed gradient insert (gradient strength: 200 mT/m, slew rate: 600 T/m/s). To further shorten the echo time, Stejskal‐Tanner diffusion encoding with a single‐shot spiral readout was implemented. To allow non‐Cartesian image reconstruction using such strong and fast gradients, the characterization of eddy current and concomitant field effects was performed based on field‐camera measurements. Results An echo time of only 19 ms was achieved for a b‐factor of 1000 s/mm2. An in‐plane resolution of 0.68 mm was encoded by a single‐shot spiral readout of 40.5 ms using 3‐fold undersampling. The resulting images did not suffer from off‐resonance artifacts and T2∗ blurring that are common to single‐shot images acquired with regular gradient systems. Conclusion Spiral diffusion imaging using a head gradient system, together with an accurate characterization of the encoding process allows for a substantial reduction of the echo time, and improves the achievable resolution in motion‐insensitive single‐shot DWI.

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Diffusion dispersion imaging: Mapping oscillating gradient spin‐echo frequency dependence in the human brain

Cited by 43 publications

References 38 publications

Improved gradient waveforms for oscillating gradient spin‐echo (OGSE) diffusion tensor imaging

Improved gradient waveforms for oscillating gradient spin‐echo (OGSE) diffusion tensor imaging

Oscillating diffusion‐encoding with a high gradient‐amplitude and high slew‐rate head‐only gradient for human brain imaging

Minimizing the echo time in diffusion imaging using spiral readouts and a head gradient system

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