SDR

PLoS ONE: Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI

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Noam Shemesh, Gonzalo A. Álvarez, Lucio Frydman

Published: July 21, 2015

DOI: 10.1371/journal.pone.0133201

Abstract

Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems – ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Ec​ho(NOGSE), can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length)^6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE’s ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions – where the ground truth can be determined from ancillary microscopy – corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE’s potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development.

Citation: Shemesh N, Álvarez GA, Frydman L (2015) Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI. PLoS ONE 10(7): e0133201. doi:10.1371/journal.pone.0133201

Editor: Ichio Aoki, National Institute of Radiological Sciences, JAPAN

Received: November 25, 2014; Accepted: June 24, 2015; Published: July 21, 2015

Copyright: © 2015 Shemesh et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

 

via PLOS ONE: Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI.

 

Magnetic resonance virtual histology
Magnetic resonance virtual histology based on probing molecular diffusion in tissues. Non-uniform oscillating gradient spin-echo (NOGSE) sequences are applied to generate the magnetic resonance imaging (MRI) contrast. The compartment size distributions in a mouse corpus callosum are extracted highlighting the different anatomical regions.
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Diffusion-assisted selective dynamical recoupling: A new approach to measure background gradients in magnetic resonance | J. Chem. Phys. (2014)

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Diffusion-assisted selective dynamical recoupling: A new approach to measure background gradients in magnetic resonance

Gonzalo A. Álvarez, Noam Shemesh and Lucio Frydman
J. Chem. Phys. 140, 084205 (2014); http://dx.doi.org/10.1063/1.4865335

Dynamical decoupling, a generalization of the original NMR spin-echo sequence, is becoming increasingly relevant as a tool for reducing decoherence in quantum systems. Such sequences apply non-equidistant refocusing pulses for optimizing the coupling between systems, and environmental fluctuations characterized by a given noise spectrum. One such sequence, dubbed Selective Dynamical Recoupling SDR [P. E. S. Smith, G. Bensky, G. A. Álvarez, G. Kurizki, and L. Frydman, Proc. Natl. Acad. Sci. 109, 5958 (2012)], allows one to coherently reintroduce diffusion decoherence effects driven by fluctuations arising from restricted molecular diffusion [G. A. Álvarez, N. Shemesh, and L. Frydman, Phys. Rev. Lett. 111, 080404 (2013)]. The fully-refocused, constant-time, and constant-number-of-pulses nature of SDR also allows one to filter out “intrinsic” T1 and T2 weightings, as well as pulse errors acting as additional sources of decoherence. This article explores such features when the fluctuations are now driven by unrestricted molecular diffusion. In particular, we show that diffusion-driven SDR can be exploited to investigate the decoherence arising from the frequency fluctuations imposed by internal gradients. As a result, SDR presents a unique way of probing and characterizing these internal magnetic fields, given an a priori known free diffusion coefficient. This has important implications in studies of structured systems, including porous media and live tissues, where the internal gradients may serve as fingerprints for the systems composition or structure. The principles of this method, along with full analytical solutions for the unrestricted diffusion-driven modulation of the SDR signal, are presented. The potential of this approach is demonstrated with the generation of a novel source of MRI contrast, based on the background gradients active in an ex vivo mouse brain. Additional features and limitations of this new method are discussed.

© 2014 AIP Publishing LLC

via Diffusion-assisted selective dynamical recoupling: A new approach to measure background gradients in magnetic resonance, J. Chem. Phys. 140, 084205 (2014); http://dx.doi.org/10.1063/1.4865335.

Selective dynamical recoupling (SDR) series of images and the corresponding ex-vivo mouse brain background gradients (central panel) derived from these data.
Selective dynamical recoupling (SDR) series of images and the corresponding ex-vivo mouse brain background gradients (central panel) derived from these data.

Coherent dynamical recoupling of diffusion-driven decoherence in magnetic resonance | Phys. Rev. Lett. 111, 080404 (2013)

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Coherent dynamical recoupling of diffusion-driven decoherence in magnetic resonance

Gonzalo A. Álvarez, Noam Shemesh, and Lucio Frydman
Department of Chemical Physics, Weizmann Institute of Science, Rehovot, 76100, Israel
Received 13 May 2013; published 20 August 2013

During recent years, dynamical decoupling (DD) has gained relevance as a tool for manipulating and interrogating quantum systems. This is particularly relevant for spins involved in nuclear magnetic resonance (NMR), where DD sequences can be used to prolong quantum coherences, or to selectively couple or decouple the effects imposed by random environmental fluctuations. In this Letter, we show that these concepts can be exploited to selectively recouple diffusion processes in restricted spaces. The ensuing method provides a novel tool to measure restriction lengths in confined systems such as capillaries, pores or cells. The principles of this method for selectively recoupling diffusion-driven decoherence, its standing within the context of diffusion NMR, extensions to the characterization of other kinds of quantum fluctuations, and corroborating experiments, are presented.

© 2013 American Physical Society

via Phys. Rev. Lett. 111, 080404 (2013): Coherent Dynamical Recoupling of Diffusion-Driven Decoherence in Magnetic Resonance.

arXiv: [1305.2794] Coherent dynamical recoupling of diffusion-driven decoherence in magnetic resonance.

Time evolution of the spin magnetization under CPMG (N = 8 pulses) and Hahn-echo sequences for spins diffusing in a restricted space (circles, triangles), and under free diffusion (crosses, dashes). The solid black lines show the time range where the restricted diffusion effects dominate; the difference ∆M_SDR between these lines gives a contrast, over which signals can be coherently modulated by a suitable Selective Dynamical Decoupling (SDR) filter function.
Time evolution of the spin magnetization under CPMG (N = 8 pulses) and Hahn-echo sequences for spins diffusing in a restricted space (circles, triangles), and under free diffusion (crosses, dashes). The solid black lines show the time range where the restricted diffusion effects dominate; the difference ∆M_SDR between these lines gives a contrast, over which signals can be coherently modulated by a suitable Selective Dynamical Decoupling (SDR) filter function.
Experimental SDR signals normalized with the first data point (symbols) as a function of the x delays of the SDR sequence. The solid lines are analytical fittings of our model to the experimental curve. By using the measured diffusion coefficient D0 ∼ 2.3 × 10−5 cm^2/s, the fitted diameter d given in the plots is in agreement with the nominal value d = 5 ± 1μm.
Experimental SDR signals normalized with the first data point (symbols) as a function of the x delays of the SDR sequence. The solid lines are analytical fittings of our model to the experimental curve. By using the measured diffusion coefficient D0 ∼ 2.3 × 10−5 cm^2/s, the fitted diameter d given in the plots is in agreement with the nominal value d = 5 ± 1μm. The behavior of the SDR curves resemble the root mean square displacement of the diffusing spins in a restricted space: in both cases curves plateu for times x larger than the correlation time characteristic of achieving a restricted diffusion regime, evidence a full sampling of the restricting space.