| 1. |
- Reymbaut, A., et al.
(författare)
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Clinical Research with Advanced Diffusion Encoding Methods in MRI
- 2020
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Ingår i: Advanced Diffusion Encoding Methods in MRI. - Cambridge : Royal Society of Chemistry. - 2044-253X .- 2044-2548. ; 2020-January:24, s. 406-429
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Bokkapitel (refereegranskat)abstract
- This chapter offers a comprehensive summary of applications of advanced diffusion encoding methods in MRI within a narrowly defined area of in vivo human measurements with imaging read-out and voxel-by-voxel data analysis. The list of methods comprises tensor-valued encoding to investigate cell densities, shapes, and orientations in heterogeneous tissues, time/frequency-dependent encoding for estimating structural length scales, adjustable velocity-encoding to monitor flow in the microcapillary network, double encoding with varying mixing times to assess diffusional exchange between distinct tissue microenvironments and across cell membranes, and relaxation-diffusion correlation to resolve and separately characterize tissue microenvironments in terms of their local chemical composition and microstructure. The shown examples include proof-of-concept measurements on healthy volunteers, pilot investigations of pathologies, and clinical research involving 10-100 subjects. Studied organs include brain, breast, prostate, liver, kidney, placenta, muscle, and peripheral nerve, with examples of pathologies from tumors, schizophrenia, multiple sclerosis, stroke, neurocysticercosis, pre-eclampsia, and chronic exertional compartment syndrome.
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| 2. |
- Shemesh, Noam, et al.
(författare)
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Conventions and nomenclature for double diffusion encoding NMR and MRI.
- 2016
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 75:1, s. 82-87
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Forskningsöversikt (refereegranskat)abstract
- Stejskal and Tanner's ingenious pulsed field gradient design from 1965 has made diffusion NMR and MRI the mainstay of most studies seeking to resolve microstructural information in porous systems in general and biological systems in particular. Methods extending beyond Stejskal and Tanner's design, such as double diffusion encoding (DDE) NMR and MRI, may provide novel quantifiable metrics that are less easily inferred from conventional diffusion acquisitions. Despite the growing interest on the topic, the terminology for the pulse sequences, their parameters, and the metrics that can be derived from them remains inconsistent and disparate among groups active in DDE. Here, we present a consensus of those groups on terminology for DDE sequences and associated concepts. Furthermore, the regimes in which DDE metrics appear to provide microstructural information that cannot be achieved using more conventional counterparts (in a model-free fashion) are elucidated. We highlight in particular DDE's potential for determining microscopic diffusion anisotropy and microscopic fractional anisotropy, which offer metrics of microscopic features independent of orientation dispersion and thus provide information complementary to the standard, macroscopic, fractional anisotropy conventionally obtained by diffusion MR. Finally, we discuss future vistas and perspectives for DDE. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.
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| 3. |
- Topgaard, D., et al.
(författare)
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Translational Motion of Water in Biological Tissues-A Brief Primer
- 2020
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Ingår i: Advanced Diffusion Encoding Methods in MRI. - Cambridge : Royal Society of Chemistry. - 2044-253X .- 2044-2548. - 9781788017268 - 9781788019910 ; 2020-January:24, s. 1-11
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Bokkapitel (refereegranskat)abstract
- As an introduction to the rigorous treatment of diffusion encoding in the rest of the book, this chapter gives simple non-mathematical explanations of the relations between the properties of biological tissues and the translational motion of the tissue water with the aim of conveying an intuitive feel of the relevant time and length scales and the level of detail of the information that can be obtained. The influence of biomembranes and macromolecules on water dynamics is reviewed from both molecular and cellular scale perspectives. The potentially complex motion patterns are decomposed into short-time diffusivity, restriction, anisotropy, flow, and exchange, which can be independently assessed and correlated with advanced diffusion encoding methods in MRI.
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| 4. |
- Agzenai, Y, et al.
(författare)
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In Situ X-ray Polymerization: From Swollen Lamellae to Polymer-Surfactant Complexes
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:4, s. 1159-1167
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the monomer diallyldimethylammonium chloride (D) on the lamellar liquid crystal formed by the anionic surfactant aerosol OT (AOT) and water is investigated, determining the lamellar spacings by SAXS and the quadrupolar splittings by deuterium NMR, as a function of the D or AOT concentrations. The cationic monomer D induces a destabilization of the AOT lamellar structure such that, at a critical concentration higher than 5 wt %, macroscopic phase separation takes place. When the monomer, which is dissolved in the AOT lamellae, is polymerized in situ by X-ray initiation, a new collapsed lamellar phase appears, corresponding to the complexation of the surfactant with the resulting polymer. A theoretical model is employed to analyze the variation of the interactions between the AOT bilayers and the stability of the lamellar structure.
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| 5. |
- Ahlgren, André, et al.
(författare)
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Quantification of microcirculatory parameters by joint analysis of flow-compensated and non-flow-compensated intravoxel incoherent motion (IVIM) data.
- 2016
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Ingår i: NMR in Biomedicine. - : Wiley. - 0952-3480 .- 1099-1492. ; 29:5, s. 640-649
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to improve the accuracy and precision of perfusion fraction and blood velocity dispersion estimates in intravoxel incoherent motion (IVIM) imaging, using joint analysis of flow-compensated and non-flow-compensated motion-encoded MRI data. A double diffusion encoding sequence capable of switching between flow-compensated and non-flow-compensated encoding modes was implemented. In vivo brain data were collected in eight healthy volunteers and processed using the joint analysis. Simulations were used to compare the performance of the proposed analysis method with conventional IVIM analysis. With flow compensation, strong rephasing was observed for the in vivo data, approximately cancelling the IVIM effect. The joint analysis yielded physiologically reasonable perfusion fraction maps. Estimated perfusion fractions were 2.43 ± 0.81% in gray matter, 1.81 ± 0.90% in deep gray matter, and 1.64 ± 0.72% in white matter (mean ± SD, n = 8). Simulations showed improved accuracy and precision when using joint analysis of flow-compensated and non-flow-compensated data, compared with conventional IVIM analysis. Double diffusion encoding with flow compensation was feasible for in vivo imaging of the perfusion fraction in the brain. The strong rephasing implied that blood flowing through the cerebral microvascular system was closer to the ballistic limit than the diffusive limit. © 2016 The Authors NMR in Biomedicine published by John Wiley & Sons Ltd.
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| 6. |
- Algotsson, Jenny, et al.
(författare)
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Electrostatic interactions are important for the distribution of Gd(DTPA)(2-) in articular cartilage.
- 2015
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 76:2, s. 500-509
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Tidskriftsartikel (refereegranskat)abstract
- The delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) method can be used to assess the content of glycosaminoglycan in cartilage. In in vitro and model studies, the content of glycosaminoglycan is often expressed in terms of a fixed charge density (FCD). Values of the fixed charge density obtained using the dGEMRIC method differs from values obtained using other methods. The purpose of this work was to further clarify the origin of this discrepancy.
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| 7. |
- Algotsson, Jenny, et al.
(författare)
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Intermolecular interactions play a role in the distribution and transport of charged contrast agents in a cartilage model
- 2019
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 14:10
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Tidskriftsartikel (refereegranskat)abstract
- The transport and distribution of charged molecules in polyelectrolyte solutions are of both fundamental and practical importance. A practical example, which is the specific subject addressed in the present paper, is the transport and distribution of charged species into cartilage. The charged species could be a contrast agent or a drug molecule involved in diagnosis or treatment of the widespread degenerative disease osteoarthritis, which leads to degradation of articular cartilage. Associated scientific issues include the rate of transport and the equilibrium concentrations of the charged species in the cartilage and the synovial fluid. To address these questions, we present results from magnetic resonance micro-imaging experiments on a model system of articular cartilage. The experiments yield temporally and spatially resolved data on the transport of a negatively charged contrast agent (charge = -2), used in medical examinations of cartilage, into a polyelectrolyte solution, which is designed to capture the electrostatic interactions in cartilage. Also presented is a theoretical analysis of the transport where the relevant differential equations are solved using finite element techniques as well as treated with approximate analytical expressions. In the analysis, non-ideal effects are included in the treatment of the mobile species in the system. This is made possible by using results from previous Monte Carlo simulations. The results demonstrate the importance of taking non-idealities into account when data from measurements of transport of charged solutes in a system with fixed charges from biological polyelectrolytes are analyzed.
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| 8. |
- Alves, Luis, et al.
(författare)
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Dissolution state of cellulose in aqueous systems. 1. Alkaline solvents
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:1, s. 247-258
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Tidskriftsartikel (refereegranskat)abstract
- The understanding of the state of dissolution of cellulose in a certain solvent is a critical step forward in the development of new efficient solvent systems for cellulose. Nevertheless, obtaining such information is not trivial. Recently, polarization transfer solid-state NMR (PTssNMR) was shown to be a very promising technique regarding an efficient and robust characterization of the solution state of cellulose. In the present study, combining PTssNMR, microscopic techniques and X-ray diffraction, a set of alkaline aqueous systems are investigated. The addition of specific additives, such as urea or thiourea, to aqueous NaOH based systems as well as the use of an amphiphilic organic cation, is found to have pronounced effects on the dissolution efficiency of cellulose. Additionally, the characteristics of the regenerated material are strongly dependent on the dissolution system; typically less crystalline materials, presenting smoother morphologies, are obtained when amphiphilic solvents or additives are used.
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| 9. |
- Alves, Luis, et al.
(författare)
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Dissolution state of cellulose in aqueous systems. 2. Acidic solvents
- 2016
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 151, s. 707-715
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is insoluble in water but can be dissolved in strong acidic or alkaline conditions. How well dissolved cellulose is in solution and how it organizes are key questions often neglected in literature. The typical low pH required for dissolving cellulose in acidic solvents limits the use of typical characterization techniques. In this respect, Polarization Transfer Solid State NMR (PT ssNMR) emerges as a reliable alternative. In this work, combining PT ssNMR, microscopic techniques and X-ray diffraction, a set of different acidic systems (phosphoric acid/water, sulfuric acid/glycerol and zinc chloride/water) is investigated. The studied solvent systems are capable to efficiently dissolve cellulose, although degradation occurs to some extent. PT ssNMR is capable to identify the liquid and solid fractions of cellulose, the degradation products and it is also sensitive to gelation. The materials regenerated from the acidic dopes were found to be highly sensitive to the solvent system and to the presence of amphiphilic additives in solution.
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| 10. |
- Alves, Luis, et al.
(författare)
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New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
- 2018
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Ingår i: GELS. - : MDPI AG. - 2310-2861. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 degrees C for a system containing 5wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.
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