Novel diffusion anisotropy indices: An evaluation

Wang, Jiun‐Jie; Chao, Tsi-Chian; Wai, Yau‐Yau; Hsu, Yuan-Yu

doi:10.1002/jmri.20616

Cited by 16 publications

(12 citation statements)

References 22 publications

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“…The ferromagnetic contribution on magnetoresistance GMR FM is enhanced with increasing m Fe , while the superparamagnetic contribution on magnetoresistance GMR SPM is decreased. With increasing m Fe , the number of multidomain granules is increased and the number of superparamagnetic granules is reduced, and the ratio of GMR FM /GMR SPM is enhanced with increasing m Fe , which is consistent with the theoretic prediction of magnetoresistance in granular films [29,30] where multidomain granules or superparamagnetic granules play a primary role, respectively.…”

Section: Methodssupporting

confidence: 84%

Magnetic Properties and Magnetoresistance in Fe-ITO Granular Films

Tian

Chen²,

et al. 2010

Metall Mater Trans A

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Fe-ITO granular films with various volume fractions of Fe were prepared using the radio frequency (RF) co-sputtering technique. The magnetic and magnetoresistance properties were investigated. A transition from superparamagnetic granular films to ferromagnetic multidomain granular films with increasing the volume fraction of Fe is observed. The magnetoresistance of sample with low volume fraction of Fe follows (M/M S ) 2 , while the magnetoresistance of samples with high volume fraction of Fe is composed of a ferromagnetic and a superparamagnetic contribution that is likely caused by the presence of small isolated superparamagnetic granules and interconnected or larger granules of ferromagnetic Fe. Further morphological and crystallographic analysis is required to fully establish the explanation.

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Section: Methodssupporting

confidence: 84%

Magnetic Properties and Magnetoresistance in Fe-ITO Granular Films

Tian

Chen²,

et al. 2010

Metall Mater Trans A

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“…Because DTI methodologies were developed particularly for the mapping of fiber tracts within the brain, and because nerve fibers are cylindrically symmetrical in their morphology, assessing tensors of cylindrical symmetry is of particular interest [6, 10, 15]. Cylindrical symmetry refers to instances in which a tensor has two identical eigenvalues (e.g.…”

Section: Theorymentioning

confidence: 99%

“…λ 1 ≠λ 2 ). Whereas some investigators use the so-called eigenvalue ratio, λ 1 /λ 2 , as a simplified index of cylindrical symmetry[6, 18], DAIs are most commonly examined and compared as indices of anisotropy for tensors with cylindrical symmetry “ A ” [7, 9, 14, 15], in which…”

Section: Theorymentioning

confidence: 99%

“…Fractional Anisotropy (FA) and Relative Anisotropy (RA) are two of the better-known DAIs. FA is the most commonly used of the DAIs because it is relatively more immune to noise [4–6] and has a higher contrast-to-noise ratio (CNR) than RA and the other DAIs [6–8]. Despite these useful features, FA is known to suffer considerably from sensitivity to noise [9–11], which can introduce bias into the quantification of diffusion anisotropy when using this index.…”

Section: Introductionmentioning

confidence: 99%

“…For example, three newer indices [6] that nominally measure a tensor’s amplitude, area, and volume are essentially functions of FA, RA, UA, or VR.…”

Section: Introductionmentioning

confidence: 99%

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The ellipsoidal area ratio: an alternative anisotropy index for diffusion tensor imaging

Cui

Bansal

et al. 2009

Magnetic Resonance Imaging

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In the processing and analysis of Diffusion Tensor Imaging (DTI) data, certain predefined morphological features of diffusion tensors are often represented as simplified scalar indices, termed Diffusion Anisotropy Indices (DAIs). When comparing tensor morphologies across differing voxels of an image, or across corresponding voxels in different images, DAIs are mathematically and statistically more tractable than are the full tensors, which are probabilistic ellipsoids consisting of 3 orthogonal vectors that each has a direction and an associated scalar magnitude. We have developed a new DAI, the “Ellipsoidal Area Ratio” (EAR), to represent the degree of anisotropy in the morphological features of a diffusion tensor. The EAR is a normalized geometrical measure of surface curvature in the 3D diffusion ellipsoid. Monte Carlo simulations and applications to the study of in vivo human data demonstrate that, at low noise levels, EAR provides a similar contrast-to-noise ratio (CNR) but a higher signal-to-noise ratio (SNR) than does fractional anisotropy (FA), which is currently the most popular anisotropy index in active use. Moreover, at the high noise levels encountered most commonly in real-world DTI datasets, EAR compared with FA is consistently much more robust to perturbations from noise and it provides a higher CNR, features useful for the analysis of DTI data that are inherently noise-sensitive.

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Spatial mapping of translational diffusion coefficients using diffusion tensor imaging: A mathematical description

Shetty

Chiang

Maletić-Savatić

et al. 2014

Concepts Magnetic Resonance

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In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal–Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain.

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Novel diffusion anisotropy indices: An evaluation

Cited by 16 publications

References 22 publications

Magnetic Properties and Magnetoresistance in Fe-ITO Granular Films

Magnetic Properties and Magnetoresistance in Fe-ITO Granular Films

The ellipsoidal area ratio: an alternative anisotropy index for diffusion tensor imaging

Spatial mapping of translational diffusion coefficients using diffusion tensor imaging: A mathematical description

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