Tissue characterization using R1rho dispersion imaging at low locking fields

Adelnia, Fatemeh; Zu, Zhongliang; Spear, John T.; Wang, Feng; Harkins, Kevin D.; Gore, John C.

doi:10.1016/j.mri.2021.05.006

Cited by 8 publications

(16 citation statements)

References 53 publications

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“…20 Contrast to the intrinsic dipolar interactions on fast timescales, the effect of slow molecular motions on ܴ ଶ can be suppressed by ܴ ଵఘ dispersion. 46,69 The fitted ܴ ଶ was reduced in developing (Figure 7A) and pathological (Figure 8C) WM compared to that in the healthy brain, consistent with fewer macromolecular labile protons. It was also shown 41 that ܴ ଶ was considerably larger at 7T ex vivo when compared to those at 3T in vivo, possibly due to an increased ‫ܤ‬ inhomogeneity.…”

Section: Isotropic Relaxation Contributionsmentioning

confidence: 75%

“…Whereas the value of D a for restricted water seems not unreasonable in WM in vivo, the value of τ b is uncertain. 46, 67 More research is thus warranted.…”

Section: Discussionmentioning

confidence: 99%

“…4, the observed proton MR transverse relaxation rates were divided into isotropic and anisotropic components, essentially assuming fast spin exchange between two environments. 68 The former may arise from several relaxation pathways such as intrinsic dipolar interactions modulated by fast (e.g., pico- and nanoseconds) timescales of molecular motions, 2, 50 chemical exchange and diffusion due to slow (e.g., micro- and milliseconds) molecular motions, 46 and non-local magnetic susceptibility inhomogeneity if gradient echo rather than spin echo signal was used. 20 Contrast to the intrinsic dipolar interactions on fast timescales, the effect of slow molecular motions on can be suppressed by R 1 ρ dispersion.…”

Section: Discussionmentioning

confidence: 99%

“…20 Contrast to the intrinsic dipolar interactions on fast timescales, the effect of slow molecular motions on can be suppressed by R 1 ρ dispersion. 46, 69…”

Section: Discussionmentioning

confidence: 99%

“…To conceptually connect an anisotropic rotational motion with an anisotropic translational diffusion, a standard axially symmetric system (Figure 3A) could be transformed into a cylindrical helix model (Figure 3C). Although sharing the same geometric microstructure, the proposed model is radically different from the previously developed hollow cylinder fiber model (HCFM) 44-46 , with the former derived from intramolecular residual dipolar interactions but the latter based on the “susceptibility effect”. Further, the proposed model deals exclusively with anisotropic R 2 originating from both within (Fig.…”

Section: Theorymentioning

confidence: 93%

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

Pang

2021

Preprint

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Purpose: To overcome limitations of prior orientation-dependent R2 and R2* formalisms in white matter (WM) with a novel framework based on magic angle effect. Methods: A cylindrical helix model was developed embracing both anisotropic rotational and translational diffusions of ordered water in WM, with the former characterized by an axially symmetric system. Both R2 and R2* were divided into isotropic (R2i) and anisotropic parts, R2a*f(ε-ε0,α), with α denoting a funnel opening angle and ε0 an orientation (ε) offset relative to DTI-derived primary diffusivity direction. The proposed framework (Fit A) was compared with prior model without ε0 (Fit B) and applied to published R2 and R2* in WM of underdeveloped, healthy, and diseased conditions. Goodness of fit was characterized by root-mean-square error (RMSE). F-test and Pearson correlation coefficient (PCC) were used with statistical significance set to P ≤ .05. Results: Fit A significantly outperformed Fit B as demonstrated by reduced RMSEs in myelin water (i.e., 0.349 vs. 0.724). The fitted ε0 was in good agreement with the calculated ε0 from DTI directional diffusivities. Significant positive (R2i) and negative (α and R2a) correlations were found with aging (demyelination) in adults while ε0 showed a weak positive correction (PCC=0.11, P= .28). Compared to those from healthy adult WM, the fits of R2i, R2a, and α from neonates were considerably reduced but ε0 increased, consistent with limited myelination. Conclusion: The developed framework can better characterize anisotropic transverse relaxation in WM, shedding new light on myelin microstructural alterations at the molecular level.

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Section: Isotropic Relaxation Contributionsmentioning

confidence: 75%

“…Whereas the value of D a for restricted water seems not unreasonable in WM in vivo, the value of τ b is uncertain. 46, 67 More research is thus warranted.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…20 Contrast to the intrinsic dipolar interactions on fast timescales, the effect of slow molecular motions on can be suppressed by R 1 ρ dispersion. 46, 69…”

Section: Discussionmentioning

confidence: 99%

Section: Theorymentioning

confidence: 93%

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

Pang

2021

Preprint

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A robust adiabatic constant amplitude spin‐lock preparation module for myocardial T_1ρ quantification at 3 T

et al. 2022

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T 1ρ quantification has the potential to assess myocardial fibrosis without contrast agent. However, its preparation spin-lock pulse is sensitive to B 1 and B 0 inhomogeneities, resulting in severe banding artifacts in the heart region, especially at high magnetic field such as 3 T. We aimed to design a robust spin-lock (SL) preparation module that can be used in myocardial T 1ρ quantification at 3 T. We used the tan/tanh pulse to tip up and tip down the magnetization in the spin-lock preparation module (tan/tanh-SL). Bloch simulation was used to optimize pulse shape parameters of the tan/tanh with a pulse duration (T p ) of 8, 4, and 2 ms, respectively. The designed tan/tanh-SL modules were implemented on a 3-T MR scanner. They were evaluated in phantom studies under three different cases of B 0 and B 1 inhomogeneities, and tested in cardiac T 1ρ quantification of healthy volunteers. The performance of the tan/tanh-SL was compared with the composite SL preparation pulses and the commonly used hyperbolic secant pulse for spin-lock (HS-SL). Feasible pulse shape parameters were obtained using Bloch simulation. Compared with HS-SL, the quantification error of tan/tanh-SL was reduced by 27.7% for T p = 8 ms (mean ΔQ = 126.15 vs. 174.42) and 75.6% for T p = 4 ms (mean ΔQ = 136.65 vs. 559.53).In the phantom study, tan/tanh-SL was less sensitive to B 1 and B 0 inhomogeneity compared with composite SL pulses and HS-SL. In cardiac T 1ρ quantification, the T 1ρ maps using tan/tanh-SL showed fewer banding artifacts than using composite SL pulses and HS-SL. The proposed tan/tanh-SL preparation module greatly improves the robustness to B 0 and B 1 field inhomogeneities and can be used in cardiac T 1ρ quantification at 3 T.

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An adiabatic RF pulse in spin‐lock preparations: A double‐edged sword for quantitative R1ρ imaging in clinical applications

Pang

2023

NMR in Biomedicine

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Adiabatic RF pulses are often used in quantitative R1ρ imaging because of their exceptional immunities to nonuniform magnetic B0 and B1 fields. However, the previously reported R1ρ values in biological tissues were comparatively reduced because of an overlooked T1 relaxation effect within a lengthy pulse duration Tp. This Letter aimed to remind the readers that an adiabatically prepared spin‐locking scheme could introduce bias to R1ρ quantification and thus its nonadiabatic alternative is preferred, particularly for R1ρ dispersion studies.

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Tissue characterization using R1rho dispersion imaging at low locking fields

Cited by 8 publications

References 53 publications

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

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

A robust adiabatic constant amplitude spin‐lock preparation module for myocardial T_1ρ quantification at 3 T

An adiabatic RF pulse in spin‐lock preparations: A double‐edged sword for quantitative R1ρ imaging in clinical applications

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Tissue characterization using R1rho dispersion imaging at low locking fields

Cited by 8 publications

References 53 publications

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

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

A robust adiabatic constant amplitude spin‐lock preparation module for myocardial T1ρ quantification at 3 T

An adiabatic RF pulse in spin‐lock preparations: A double‐edged sword for quantitative R1ρ imaging in clinical applications

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A robust adiabatic constant amplitude spin‐lock preparation module for myocardial T_1ρ quantification at 3 T