An efficient <i>R</i><sub>1ρ</sub> dispersion imaging method for human knee cartilage using constant magnetization prepared turbo‐FLASH

Pang, Yuxi; Palmieri-Smith, Riann M.; Maerz, Tristan

doi:10.1002/nbm.4500

Cited by 7 publications

(8 citation statements)

References 47 publications

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“…Utilizing fully adiabatic spin locking 22,24,29,37,38 can further mitigate the effects of field inhomogeneities and even provide slice selectivity 37 as well as reduced orientation/magic angle dependence 7 . A variation of the double‐refocused hard‐pulse preparation scheme investigated here 18 was presented recently with promising results, but without direct comparison with other preparation methods 48 . Besides presenting a method for faster T 1ρ acquisition by using tailored variable flip angle scheduling, Johnson et al 45 also utilized a partially adiabatic variation of the single‐refocus method by Witschey et al, 14 replacing the hard 90° pulses with adiabatic pulses.…”

Section: Discussionmentioning

confidence: 99%

New methods for robust continuous wave T_1ρ relaxation preparation

et al. 2022

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Measurement of the longitudinal relaxation time in the rotating frame of reference (T1ρ) is sensitive to the fidelity of the main imaging magnetic field (B0) and that of the RF pulse (B1). The purpose of this study was to introduce methods for producing continuous wave (CW) T1ρ contrast with improved robustness against field inhomogeneities and to compare the sensitivities of several existing and the novel T1ρ contrast generation methods with the B0 and B1 field inhomogeneities. Four hard‐pulse and four adiabatic CW‐T1ρ magnetization preparations were investigated. Bloch simulations and experimental measurements at different spin‐lock amplitudes under ideal and non‐ideal conditions, as well as theoretical analysis of the hard‐pulse preparations, were conducted to assess the sensitivity of the methods to field inhomogeneities, at low (ω1 << ΔB0) and high (ω1 >> ΔB0) spin‐locking field strengths. In simulations, previously reported single‐refocus and new triple‐refocus hard‐pulse and double‐refocus adiabatic preparation schemes were found to be the most robust. The mean normalized absolute deviation between the experimentally measured relaxation times under ideal and non‐ideal conditions was found to be smallest for the refocused preparation schemes and broadly in agreement with the sensitivities observed in simulations. Experimentally, all refocused preparations performed better than those that were non‐refocused. The findings promote the use of the previously reported hard‐pulse single‐refocus ΔB0 and B1 insensitive T1ρ as a robust method with minimal RF energy deposition. The double‐refocus adiabatic B1 insensitive rotation‐4 CW‐T1ρ preparation offers further improved insensitivity to field variations, but because of the extra RF deposition, may be preferred for ex vivo applications.

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Section: Discussionmentioning

confidence: 99%

New methods for robust continuous wave T_1ρ relaxation preparation

et al. 2022

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“…An intrinsic orientation-independent metric for each image voxel could be deduced from R l ρ dispersion imaging 30 as recently demonstrated on articular cartilage. 32, 69…”

Section: Discussionmentioning

confidence: 99%

On the origin ofR₂orientation dependence angle offsets in white matter

Pang

2022

Preprint

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Purpose: to identify the origin of confounding angle offset ε_0 in R2 orientation dependence and to propose a novel framework for better characterizing anisotropic R2 in brain white matter (WM). Methods: Anisotropic (ε) rather than principal diffusivity direction (Φ) was theorized along axon fiber, with ε determined by all eigenvalues and eigenvectors from diffusion tensor. An extra parameter ε_0 was introduced into generalized magic angle effect function to account for any offset in R2 orientation dependence derived from T2-weighted image (b=0). These dependences referenced by ε were compared to those referenced as usual by Φ at b-values of 1000 and 2000 (s/mm2) on both linear and planar tensor image voxels in WM, based on public domain ultrahigh-resolution (760 μm3) Connectome DTI datasets of a healthy young adult brain. A Student's t-test was used to assess the mean differences and the statistical significance was considered at P < 0.05. Results: Fitted ε_0 became zero if referenced by ε or nonzero if referenced by Φ, signifying the origin of ε_0. Nonzero ε_0 relied on b-values and tensor shapes so did other model parameters, e.g., the amplitude of anisotropic R2 (1/s) significantly increased when using a higher b-value for the linear tensor image voxels, i.e., 3.3 ± 0.1 vs. 1.8 ± 0.1, P < 0.01. Conclusion: The origin of R2 orientation dependence angle offsets has been identified and the combined anisotropic diffusion and transverse relaxation models have fully quantified R2 orientational anisotropies, thus providing novel insights otherwise unattainable on microstructural alterations in WM.

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“…55 This experimental result justifies the relaxation mechanism underlying the proposed model, in excellent agreement with the previous finding in knee articular cartilage. 36, 56…”

Section: Discussionmentioning

confidence: 99%

“…Even though the measured orientation-dependent dispersion imaging has been demonstrated for deriving an orientation-independent order parameter in articular cartilage; 48,49 thus, more research is warranted in neuroimaging along the same line as done in musculoskeletal imaging.…”

Section: 6| An Orientation-independent Mr Metric From An Anisotropic In Wmmentioning

confidence: 99%

“…R 1 ρ comprised a constant (ISO) and two dispersed components: (1) chemical exchange effect (CHEX) and (2) residual dipolar interactions (RDD) as demonstrated previously. 60 All orientation-independent and B 0 -dependent relaxation mechanisms (including susceptibility anisotropy) were lumped into CHEX that is proportional to . When a spin-lock amplitude ω 1 = 0, R 1 ρ became R 2 to which the relative CHEX contribution, i.e., 100*CHEX/(ISO+CHEX+RDD), was about 5% at 3T (red star, B).…”

Section: Supporting Informationmentioning

confidence: 99%

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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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An efficient R_1ρ dispersion imaging method for human knee cartilage using constant magnetization prepared turbo‐FLASH

Cited by 7 publications

References 47 publications

New methods for robust continuous wave T_1ρ relaxation preparation

New methods for robust continuous wave T_1ρ relaxation preparation

On the origin ofR₂orientation dependence angle offsets in white matter

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

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An efficient R1ρ dispersion imaging method for human knee cartilage using constant magnetization prepared turbo‐FLASH

Cited by 7 publications

References 47 publications

New methods for robust continuous wave T1ρ relaxation preparation

New methods for robust continuous wave T1ρ relaxation preparation

On the origin ofR2orientation dependence angle offsets in white matter

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

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Product

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An efficient R_1ρ dispersion imaging method for human knee cartilage using constant magnetization prepared turbo‐FLASH

New methods for robust continuous wave T_1ρ relaxation preparation

New methods for robust continuous wave T_1ρ relaxation preparation

On the origin ofR₂orientation dependence angle offsets in white matter