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Purpose: Recent studies indicate that T1 in white matter (WM) is influenced by fiber orientation in B0. The purpose of the study was to investigate the interrelationships between axon fiber orientation in corpus callosum (CC) and T1 relaxation time in humans in vivo as well as in rat brain ex vivo. Methods: Volunteers were scanned for relaxometric and diffusion MRI at 3 T and 7 T. Angular T1 plots from WM were computed using fractional anisotropy and fiber‐to‐field‐angle maps. T1 and fiber‐to‐field angle were measured in five sections of CC to estimate the effects of inherently varying fiber orientations on T1 within the same tracts in vivo. Ex vivo rat‐brain preparation encompassing posterior CC was rotated in B0 and T1, and diffusion MRI images acquired at 9.4 T. T1 angular plots were determined at several rotation angles in B0. Results: Angular T1 plots from global WM provided reference for estimated fiber orientation–linked T1 changes within CC. In anterior midbody of CC in vivo, where small axons are dominantly present, a shift in axon orientation is accompanied by a change in T1, matching that estimated from WM T1 data. In CC, where large and giant axons are numerous, the measured T1 change is about 2‐fold greater than the estimated one. Ex vivo rotation of the same midsagittal CC region of interest produced angular T1 plots at 9.4 T, matching those observed at 7 T in vivo. Conclusion: These data causally link axon fiber orientation in B0 to the T1 relaxation anisotropy in WM. [ABSTRACT FROM AUTHOR]

A high degree of structural order by white matter (WM) fibre tracts creates a physicochemical environment where water relaxations are rendered anisotropic. Recently, angularly dependent longitudinal relaxation has been reported in human WM. We have characterised interrelationships between T1 relaxation and diffusion MRI microstructural indices at 3 and 7 T. Eleven volunteers consented to participate in the study. Multishell diffusion MR images were acquired with b‐values of 0/1500/3000 and 0/1000/2000 s/mm2 at 1.5 and 1.05 mm3 isotropic resolutions at 3 and 7 T, respectively. DTIFIT was used to compute DTI indices; the fibre‐to‐field angle (θFB) maps were obtained using the principal eigenvector images. The orientations and volume fractions of multiple fibre populations were estimated using BedpostX in FSL, and the orientation dispersion index (ODI) was estimated using the NODDI protocol. MP2RAGE was used to acquire images for T1 maps at 1.0 and 0.9 mm3 isotropic resolutions at 3 and 7 T, respectively. At 3 T, T1 as a function of θFB in WM with high fractional anisotropy and one‐fibre orientation volume fraction or low ODI shows a broad peak centred at 50o, but a flat baseline at 0o and 90o. The broad peak amounted up to 7% of the mean T1. At 7 T, the broad peak appeared at 40o and T1 in fibres running parallel to B0 was longer by up to 75 ms (8.3% of the mean T1) than in those perpendicular to the field. The peak at 40o was approximately 5% of mean T1 (i.e., proportionally smaller than that at 54o at 3 T). The data demonstrate T1 anisotropy in WM with high microstructural order at both fields. The angular patterns are indicative of the B0‐dependency of T1 anisotropy. Thus myelinated WM fibres influence T1 contrast both by acting as a T1 contrast agent and rendering T1 dependent on fibre orientation with B0. [ABSTRACT FROM AUTHOR]

Background and objective: Multiple factors including chemical composition and microstructure influence relaxivity of tissue water in vivo. We have quantified T1 in the human white mater (WM) together with diffusion tensor imaging to study a possible relationship between water T1, diffusional fractional anisotropy (FA) and fibre-to-field angle. Methods: An inversion recovery (IR) pulse sequence with 6 inversion times for T1 and a multi-band diffusion tensor sequence with 60 diffusion sensitizing gradient directions for FA and the fibre-to-field angle θ (between the principal direction of diffusion and B0) were used at 3 Tesla in 40 healthy subjects. T1 was assessed using the method previously applied to anisotropy of coherence lifetime to provide a heuristic demonstration as a surface plot of T1 as a function of FA and the angle θ. Results: Our data show that in the WM voxels with FA > 0.3 T1 becomes longer (i.e. 1/T1 = R1 slower) when fibre-to-field angle is 50–60°, approximating the magic angle of 54.7°. The longer T1 around the magic angle was found in a number of WM tracts independent of anatomy. S0 signal intensity, computed from IR fits, mirrored that of T1 being greater in the WM voxels when the fibre-to-field angle was 50–60°. Conclusions: The current data point to fibre-to-field-angle dependent T1 relaxation in WM as an indication of effects of microstructure on the longitudinal relaxation of water. [ABSTRACT FROM AUTHOR]

The nanostructures of nanoporous materials were studied by analyzing the anisotropy of the nuclear spin–spin and spin–lattice relaxations of the guest molecules trapped in the pores of hydrogenated amorphous silicon (a-Si:H) films. In this work the complex experimental and theoretical approach was applied to study the nanostructure of hydrogenated amorphous silicon (a-Si-H) films in the framework of the nuclear relaxation dominated by the dipole–dipole interactions. A feature of this study is the simultaneous investigation of the three (T 1 , T 1ρ , and T 2) NMR relaxation times, for the same sample. This allows us to determine not only the degree of orientation ordering of nanopores but also to estimate their size (∼ 1 nm) and correlation times of the nanopore fluctuations. The obtained results demonstrate that the developed approach is effective in studying details of nanostructure of different nanoporous materials. [Display omitted] • We report on 1H NMR experiments in (a-Si:H) films. • Spin-spin and spin–lattice relaxation times are studied. • We explain the anisotropy of the relaxation times in (a-Si:H) films. • The degree of orientational ordering of nanopores was obtained. • Estimation pore dimensions and correlation times of pore fluctuations were obtained. The aim of this work is to investigate the nanostructures of nanoporous materials by studying the anisotropy of the nuclear spin–spin and spin–lattice relaxations of the guest molecules trapped in the pores. The nuclear magnetic resonance (NMR) data are analyzed in the framework of the theory of the nuclear relaxation dominated by the dipole–dipole interactions in gas or liquid species contained in nanopores. A distinctive feature of this theory is the establishment of a relationship between the degree of orientation ordering of nanopores in the host matrix and their characteristic volume and the anisotropy of the NMR relaxation times. In this work the complex experimental and theoretical approach was applied to study the nanostructure of hydrogenated amorphous silicon (a-Si:H) films. A feature of this study is the simultaneous investigation of the three (T 1 , T 1ρ , and T 2) NMR relaxation times, for the same sample. This allows us to determine not only the degree of orientation ordering of nanopores but also to estimate their size (∼1 nm) and correlation times of the nanopore fluctuations. The obtained results demonstrate that the developed approach is effective in studying details of nanostructure of different nanoporous materials. [ABSTRACT FROM AUTHOR]

Purpose: Recent studies indicate that T 1 in white matter (WM) is influenced by fiber orientation in B 0 . The purpose of the study was to investigate the interrelationships between axon fiber orientation in corpus callosum (CC) and T 1 relaxation time in humans in vivo as well as in rat brain ex vivo., Methods: Volunteers were scanned for relaxometric and diffusion MRI at 3 T and 7 T. Angular T 1 plots from WM were computed using fractional anisotropy and fiber-to-field-angle maps. T 1 and fiber-to-field angle were measured in five sections of CC to estimate the effects of inherently varying fiber orientations on T 1 within the same tracts in vivo. Ex vivo rat-brain preparation encompassing posterior CC was rotated in B 0 and T 1 , and diffusion MRI images acquired at 9.4 T. T 1 angular plots were determined at several rotation angles in B 0 ., Results: Angular T 1 plots from global WM provided reference for estimated fiber orientation-linked T 1 changes within CC. In anterior midbody of CC in vivo, where small axons are dominantly present, a shift in axon orientation is accompanied by a change in T 1 , matching that estimated from WM T 1 data. In CC, where large and giant axons are numerous, the measured T 1 change is about 2-fold greater than the estimated one. Ex vivo rotation of the same midsagittal CC region of interest produced angular T 1 plots at 9.4 T, matching those observed at 7 T in vivo., Conclusion: These data causally link axon fiber orientation in B 0 to the T 1 relaxation anisotropy in WM., (© 2023 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Modeling the anisotropic behavior of the nuclear magnetic resonance (NMR) transverse relaxation time (T 2) allows to investigate the fibril nanostructure of biological samples (fresh celery sample in the attached Figure). Sample's nanoarchitecture was modeled as a set of water filled nanocavities (Panel 'a'). θ s is the angle between the external magnetic field and the sample's main axis Z s. θ n denotes the angle between the external magnetic field H 0 and the axis of a n -th nanocavity (Z n). Z 0 axis represents the averaged orientation of the ensemble of all nanocavities. To account for deviations of the nanocavities' orientations from Z 0 we defined the polar ζ and azimuthal ξ angles, reflecting the deviation of the main axis of each specific nanocavity (Z n) from the main Z s axis. Lastly, ζ 0 and ξ 0 are the polar and azimuthal angles which determine the deviation of the Z 0 -axis from the Z s -axis. The presented framework can be utilized explain the anisotropy the T 2 relaxation time, and specifically to determine the degree of orientational ordering of the nanocavities, their characteristic volume, and their average direction with respect to the macroscopic sample. Results show good agreement between theory and experimental data (Panel 'b'), which are, moreover, supported by optical microscopy. The quantitative NMR approach presented herein can be potentially used to determine the internal ordering of biological tissues noninvasively. [Display omitted] • We investigate of the angular dependence of NMR's transverse (T 2) relaxation time. • Used model is a fresh celery stem having ordered nanoscale architecture. • A new theoretical model can extract nanocavities orientational ordering and volume. • Model can be applied for probing nanostructure of biological tissues and materials. This study investigates the fibril nanostructure of fresh celery samples by modeling the anisotropic behavior of the transverse relaxation time (T 2) in nuclear magnetic resonance (NMR). Experimental results are interpreted within the framework of a previously developed theory, which was successfully used to model the nanostructures of several biological tissues as a set of water filled nanocavities, hence explaining the anisotropy the T 2 relaxation time in vivo. An important feature of this theory is to determine the degree of orientational ordering of the nanocavities, their characteristic volume, and their average direction with respect to the macroscopic sample. Results exhibit good agreement between theory and experimental data, which are, moreover, supported by optical microscopic resolution. The quantitative NMR approach presented herein can be potentially used to determine the internal ordering of biological tissues noninvasively. [ABSTRACT FROM AUTHOR]

The liquid crystalline (LC) polymers are considered as anisotropic viscoelastic liquids with nonsymmetric stresses. A simple constitutive equation for nematic polymers describing the coupled relaxation of symmetric and antisymmetric parts of the stress tensor is formulated. For illustration of non-symmetric anisotropic viscoelasticity, the simplest viscometric flows of polymeric nematics in the magnetic field are considered. The frequency and shear rate dependencies of extended set of Miesowicz viscosities are predicted. [ABSTRACT FROM AUTHOR]