Orientation dependent proton transverse relaxation in the human brain white matter: The magic angle effect on a cylindrical helix

Pang, Yuxi

doi:10.1101/2021.09.13.460097

Cited by 3 publications

(11 citation statements)

References 92 publications

(261 reference statements)

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“…In the past,

R_{2}^{a}

has been substituted by the myelin water fraction (MWF) 16,21 or magnetization transfer saturation (MTS) 41 in the case of

R_{2}^{*}

studies, while it simply refers to the strength of RDC in the case of

R_{2}

29 f(),αε is a normalized orientation dependence function for an axially symmetric or cone‐shaped RDC distribution surrounding an axon fiber, as depicted in Figure 1A.…”

Section: Theorymentioning

confidence: 99%

“…An imaging voxel signal

italicSO

with b = 0 in DTI may be expressed by Equation (6a), with

S_{0}

italicTE

, and

R_{2}^{\exp}

, respectively, denoting signal intensity with

italicTE = 0

, spin‐echo time, and apparent transverse relaxation rate that could be decomposed into isotropic

R_{2}^{i}

and anisotropic

R_{2}^{a} f ((),, α, ε)

components, as defined in Equation (1). 29

italicSO goodbreak= S_{0} * \exp ((), goodbreak- italicTE * R_{2}^{\exp})

\frac{\ln italicSO}{TE} goodbreak= ((), \frac{\ln S_{0}}{TE} goodbreak- R_{2}^{i}) goodbreak- R_{2}^{a} * f ((),, α, ε)

…”

Section: Theorymentioning

confidence: 99%

“…In the literature, susceptibility anisotropy has been attributed to a concentric distribution of lipid molecules within bilayers around an axon fiber 39 . Similarly, the origin of the MAE has been associated with a concentric distribution of ordered water molecules near the surface of bilayers 29,40 . Accordingly, the observed

R_{2}

R_{2}^{*}

orientation dependence profile, if guided by the PDD, ought to be phase shifted 37 .…”

Section: Introductionmentioning

confidence: 99%

“…However, for the human nervous system, the MAE remains elusive, particularly in the brains of adults, even although it has been reported in the peripheral nervous system 27,28 and recently in the brains of newborns 17 . When the standard MAE function is appropriately evaluated in a cylindrical system, such as a concentric distribution of water proton RDC around an axon fiber, a generalized MAE function can be formulated 29,30 . This generalized function can be recast into one of the previous model functions that originated from the susceptibility effect 21,23 .…”

Section: Introductionmentioning

confidence: 99%

“…17 When the standard MAE function is appropriately evaluated in a cylindrical system, such as a concentric distribution of water proton RDC around an axon fiber, a generalized MAE function can be formulated. 29,30 This generalized function can be recast into one of the previous model functions that originated from the susceptibility effect. 21,23 This finding implies that the underlying relaxation mechanisms cannot be disentangled simply based on different function forms.…”

Section: Introductionmentioning

confidence: 99%

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Phase‐shifted transverse relaxation orientation dependences in human brain white matter

Pang

2023

NMR in Biomedicine

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This work aimed to demonstrate an essential phase shift ε 0 for better quantifying R 2 and R Ã 2 in human brain white matter (WM), and to further elucidate its origin related to the directional diffusivities from standard diffusion tensor imaging (DTI). ε 0 was integrated into a proposed generalized transverse relaxation model for characterizing previously published R 2 and R Ã 2 orientation dependence profiles in brain WM, and then comparisons were made with those without ε 0 . It was theorized that anisotropic diffusivity direction ε was collinear with an axon fiber subject to all eigenvalues and eigenvectors from an apparent diffusion tensor. To corroborate the origin of ε 0 , R 2 orientation dependences referenced by ε were compared with those referenced by the standard principal diffusivity direction Φ at b-values of 1000 and 2500 (s/mm 2 ). These R 2 orientation dependences were obtained from T 2 -weighted images (b = 0) of ultrahigh-resolution Connectome DTI datasets in the public domain. A normalized root-mean-square error (NRMSE%) and an F-test were used for evaluating curve-fittings, and statistical significance was considered to be a p of 0.05 or less. A phase-shifted model resulted in significantly reduced NRMSE% compared with that without ε 0 in quantifying various R 2 and R Ã 2 profiles, both in vivo and ex vivo at multiple B 0 fields. The R 2 profiles based on Φ manifested a right-shifted phase (ε 0 > 0) at two b-values, while those based on ε became free from ε 0 . For all phase-shifted R 2 and R Ã 2 profiles, ε 0 generally depended on the directional diffusivities by tan À1 D ⊥ =D k À Á , as predicted. In summary, a ubiquitous phase shift ε 0 has been demonstrated as a prerequisite for better quantifying transverse relaxation orientation dependences in human brain WM. Furthermore, the origin of ε 0 associated with the directional diffusivities from DTI has been elucidated. These findings could have a significant impact on interpretations of prior R 2 and R Ã 2 datasets and on future research.

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“…In the past,

R_{2}^{a}

has been substituted by the myelin water fraction (MWF) 16,21 or magnetization transfer saturation (MTS) 41 in the case of

R_{2}^{*}

studies, while it simply refers to the strength of RDC in the case of

R_{2}

29 f(),αε is a normalized orientation dependence function for an axially symmetric or cone‐shaped RDC distribution surrounding an axon fiber, as depicted in Figure 1A.…”

Section: Theorymentioning

confidence: 99%

“…An imaging voxel signal

italicSO

with b = 0 in DTI may be expressed by Equation (6a), with

S_{0}

italicTE

, and

R_{2}^{\exp}

, respectively, denoting signal intensity with

italicTE = 0

, spin‐echo time, and apparent transverse relaxation rate that could be decomposed into isotropic

R_{2}^{i}

and anisotropic

R_{2}^{a} f ((),, α, ε)

components, as defined in Equation (1). 29

italicSO goodbreak= S_{0} * \exp ((), goodbreak- italicTE * R_{2}^{\exp})

\frac{\ln italicSO}{TE} goodbreak= ((), \frac{\ln S_{0}}{TE} goodbreak- R_{2}^{i}) goodbreak- R_{2}^{a} * f ((),, α, ε)

…”

Section: Theorymentioning

confidence: 99%

R_{2}

R_{2}^{*}

orientation dependence profile, if guided by the PDD, ought to be phase shifted 37 .…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Phase‐shifted transverse relaxation orientation dependences in human brain white matter

Pang

2023

NMR in Biomedicine

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Anisotropy of T₂ and T_1ρ relaxation time in articular cartilage at 3 T

Kantola,

Karjalainen,

Jaakola

et al. 2024

Magnetic Resonance in Med

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PurposeThe anisotropy of R2 and R1ρ relaxation rates in articular cartilage contains information about the collagenous structure of the tissue. Here we determine and study the anisotropic and isotropic components of T2 and T1ρ relaxation parameters in articular cartilage with a clinical 3T MRI device. Furthermore, a visual representation of the topographical variation in anisotropy is given via anisotropy mapping.MethodsEight bovine stifle joints were imaged at 22 orientations with respect to the main magnetic field using T2, continuous‐wave (CW) T1ρ, and adiabatic T1ρ mapping sequences. Relaxation rates were separated into isotropic and anisotropic relaxation components using a previously established relaxation anisotropy model. Pixel‐wise anisotropy values were determined from the relaxation‐time maps using Michelson contrast.ResultsThe relaxation rates obtained from the samples displayed notable variation depending on the sample orientation, magnetization preparation, and cartilage layer. R2 demonstrated significant anisotropy, whereas CW‐R1ρ (300 Hz) and CW‐R1ρ (500 Hz) displayed a low degree of anisotropy. Adiabatic R1ρ was largely isotropic. In the deep cartilage regions, relaxation rates were generally faster and more anisotropic than in the cartilage closer to the tissue surface. The isotropic relaxation rate components were found to have similar values regardless of measurement sequence.ConclusionsThe fitted relaxation model for T2 and T1ρ demonstrated varying amounts anisotropy, depending on magnetization preparation, and studied the articular cartilage layer. Anisotropy mapping of full joints showed varying amounts of anisotropy depending on the quantitative MRI parameter and topographical location, and in the case of T2, showed systematic changes in anisotropy across cartilage depth.

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Orientation dependent proton transverse relaxation in human brain white matter: The magic angle effect on a cylindrical helix

Pang

2023

Magnetic Resonance Imaging

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Orientation dependent proton transverse relaxation in the human brain white matter: The magic angle effect on a cylindrical helix

Cited by 3 publications

References 92 publications

Phase‐shifted transverse relaxation orientation dependences in human brain white matter

Phase‐shifted transverse relaxation orientation dependences in human brain white matter

Anisotropy of T₂ and T_1ρ relaxation time in articular cartilage at 3 T

Orientation dependent proton transverse relaxation in human brain white matter: The magic angle effect on a cylindrical helix

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Orientation dependent proton transverse relaxation in the human brain white matter: The magic angle effect on a cylindrical helix

Cited by 3 publications

References 92 publications

Phase‐shifted transverse relaxation orientation dependences in human brain white matter

Phase‐shifted transverse relaxation orientation dependences in human brain white matter

Anisotropy of T2 and T1ρ relaxation time in articular cartilage at 3 T

Orientation dependent proton transverse relaxation in human brain white matter: The magic angle effect on a cylindrical helix

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Anisotropy of T₂ and T_1ρ relaxation time in articular cartilage at 3 T