A modified pulsed gradient technique for measuring diffusion in the presence of large background gradients

Karlicek, R. F.; Lowe, I. J.

doi:10.1016/0022-2364(80)90095-5

Cited by 153 publications

(149 citation statements)

References 8 publications

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“…The same result as expression (19) was obtained in [42]. For PGSE or PGSTE experiments, the PFG signal attenuation calculated based …”

Section: Normal Diffusionsupporting

confidence: 51%

“…The results here can be easily extended to handle PFG anomalous diffusion of intramolecular MQC [27,40]. As the gradient field-induced phase evolution of an n-order intramolecular MQC is n times faster than the corresponding single quantum coherence, the PFG signal attenuation of intramolecular MQC is the same as that of single quantum coherence with an effective gradient intensity ng [42]. Therefore, for intramolecular MQC in PGSE or PGSTE experiments, the PFG signal attenuation equation is for calculating the MLF function by other methods to a desired accuracy can be found at www.mathworks.com/matlabcentral/fileexchange/8738-mittag-leffer-function, 2005.…”

Section: Virtual Phase-space Diffusion Real-space Spin Diffusionmentioning

confidence: 83%

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Analysis of PFG Anomalous Diffusion via Real-Space and Phase-Space Approaches

Lin

2018

Mathematics

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Pulsed-field gradient (PFG) diffusion experiments can be used to measure anomalous diffusion in many polymer or biological systems. However, it is still complicated to analyze PFG anomalous diffusion, particularly the finite gradient pulse width (FGPW) effect. In practical applications, the FGPW effect may not be neglected, such as in clinical diffusion magnetic resonance imaging (MRI). Here, two significantly different methods are proposed to analyze PFG anomalous diffusion: the effective phase-shift diffusion equation (EPSDE) method and a method based on observing the signal intensity at the origin. The EPSDE method describes the phase evolution in virtual phase space, while the method to observe the signal intensity at the origin describes the magnetization evolution in real space. However, these two approaches give the same general PFG signal attenuation including the FGPW effect, which can be numerically evaluated by a direct integration method. The direct integration method is fast and without overflow. It is a convenient numerical evaluation method for Mittag-Leffler function-type PFG signal attenuation. The methods here provide a clear view of spin evolution under a field gradient, and their results will help the analysis of PFG anomalous diffusion.

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“…The same result as expression (19) was obtained in [42]. For PGSE or PGSTE experiments, the PFG signal attenuation calculated based …”

Section: Normal Diffusionsupporting

confidence: 51%

Section: Virtual Phase-space Diffusion Real-space Spin Diffusionmentioning

confidence: 83%

Analysis of PFG Anomalous Diffusion via Real-Space and Phase-Space Approaches

Lin

2018

Mathematics

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“…The results were noticeably better than in an earlier study (10), because of several critical improvements in the methods: (i) The study was performed at 3T by using an eight-channel phased-array coil, instead of a head coil at 1.5T, which provides a higher signal-to-noise ratio. (ii) As an important improvement to Darquie et al (10), the diffusion MRI sequence was carefully chosen to be immune to background mesoscopic field gradients produced by local magnetic susceptibility inhomogeneities in the cortical tissue (20,21). Such susceptibility effects can, in particular, be induced by paramagnetic blood deoxyhemoglobin and result in an artifactual underestimation of the diffusion coefficient measured with most diffusion MRI sequences (22,23).…”

Section: Resultsmentioning

confidence: 99%

“…Eight oblique slices centered on calcarine fissure were selected from a rapid localization scan. To minimize residual susceptibility effects the diffusion fMRI sequence (data set A) consisted in a twice refocused spin-echo echo-planar imaging (EPI) sequence sensitized to diffusion by an interleaved pair of bipolar magnetic field gradient pulses (20,21). Acquisition parameters were as follows: slice thickness ϭ 3.8 mm with 50% gap, pixel size ϭ 3.75 2 mm 2 , generalized autocalibrating partially parallel acquisitions (GRAPPA) with 2-fold acceleration, 87 ms echo time, 1 s repetition time, 1,302 Hz bandwidth.…”

Section: Methodsmentioning

confidence: 99%

Direct and fast detection of neuronal activation in the human brain with diffusion MRI

Bihan

Urayama

Aso

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

251

280

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Using MRI, we found that a slowly diffusing water pool was expanding (1.7 ؎ 0.3%) upon activation on the human visual cortex at the detriment of a faster diffusing pool. The time course of this water phase transition preceded the activation-triggered vascular response detected by usual functional MRI by several seconds. The observed changes in water diffusion likely reflect early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion. Although the exact mechanisms remain to clarify, access to such an early and direct physiological marker of cortical activation with MRI will provide opportunities for functional neuroimaging of the human brain.ur current model of neuronal activation places great importance on transient electrical and biochemical events associated with the excitation processes. However, there is compelling evidence that activation is accompanied by other important physical phenomena. Microstructural changes in excited tissues have been observed, first from optical birefringence measurements (1, 2) and later more directly by using piezoelectric transducers (3). Those studies have revealed, for instance, that in the brain cell swelling is one of the physiological responses associated with neuronal activation (4, 5).However, such biophysical events have been monitored at the microscopic level by using invasive techniques in neuronal cell cultures or slices, and do not necessarily reflect physiological conditions (6, 7). Observing changes in cortical cell configuration in animals or humans would, thus, have a tremendous impact, because they would be directly linked to neuronal events, such as membrane expansion, and bridge the gap with current approaches to obtain images of human brain activation. Those approaches, such as blood oxygen level-dependent (BOLD) MRI, are based on blood flow changes and only indirectly and remotely related to cortical activation (8,9).A small decrease of the water diffusion coefficient during activation of human visual cortex has been previously reported by using diffusion MRI (10). Diffusion MRI provides valuable information on the microscopic obstacles which hinder diffusing molecules, such as membranes or macromolecules, and in turn, on the tissue cellular structure (11). Based on other MRI reports of water diffusivity decrease during intense neuronal activation (12, 13) or during other physiological or pathological conditions inducing cell swelling (14-17), the observed diffusion findings have been putatively ascribed to a transient swelling of cortical cells and a shrinking of the extracellular space, increasing its tortuosity (18) for diffusing molecules. However, no confirmation has been found so far for this mechanism. The aim of this report is to demonstrate that a decrease in water mobility can readily been observed in the human brain with diffusion MRI upon activation, and to provide evidence that this effect results from an early neuronal activation event that precedes the blood flow response by a sizeable time am...

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“…The bPGSTE measurements increased by 15% and 6%, while the MAGSTE measurements changed by 7% and 3%, respectively, for the 90 and 150 μm bead phantoms, providing evidence that although the heterogeneous background gradients may affect both bPGSTE and the MAGSTE measurements, the MAGSTE method is clearly less susceptible to such artifacts. In addition, the surface-to-volume ratio (S/V) was derived by fitting the normalized diffusion rate with diffusion length of short duration (i.e., ) using [24;25], (9) The S/V characterized using the MAGSTE measurements were 0.16 and 0.10 μm −1 for the 90 and 150 μm beads, respectively. On the other hand, the S/V derived using bPGSTE measurements were 0.09 and 0.08 μm −1 .…”

Section: Resultsmentioning

confidence: 99%

Improved diffusion measurement in heterogeneous systems using the magic asymmetric gradient stimulated echo (MAGSTE) technique

Sun

2007

Journal of Magnetic Resonance

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A magic asymmetric gradient stimulated echo (MAGSTE) sequence was recently proposed to improve molecular diffusion measurements in the presence of spatially varying background gradients. Its effectiveness has been demonstrated previously with simulated background gradients and in phantoms that contain bulk susceptibility differences. In this study, we investigated the MAGSTE technique in microscopically heterogeneous systems, and compared it with the conventional bipolar pulsed gradient stimulated echo (bPGSTE) sequence. We demonstrated that the MASGTE measurements, compared to the bPGSTE method, varied significantly less when the diffusion encoding/decoding interval (δ) was changed. In addition, the MAGSTE technique provided good characterization of the surface area-to-volume ratio for heterogeneous systems investigated in this study. In sum, this study showed that the MAGSTE technique provided diffusion measurements superior to those of the bPGSTE sequence, especially in the presence of severe heterogeneous background gradients.

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A modified pulsed gradient technique for measuring diffusion in the presence of large background gradients

Cited by 153 publications

References 8 publications

Analysis of PFG Anomalous Diffusion via Real-Space and Phase-Space Approaches

Analysis of PFG Anomalous Diffusion via Real-Space and Phase-Space Approaches

Direct and fast detection of neuronal activation in the human brain with diffusion MRI

Improved diffusion measurement in heterogeneous systems using the magic asymmetric gradient stimulated echo (MAGSTE) technique

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