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

Pang, Yuxi

doi:10.1016/j.mri.2023.03.010

Cited by 3 publications

(1 citation statement)

References 77 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…6,8,10,11,13 Relaxation anisotropy has been detected in various tissues, including cartilage, tendons, and white matter. 11,14,15 Various models have been used to characterize magnetic relaxation mechanisms and relaxation anisotropy. 8,11,[15][16][17][18][19][20] As OA develops, the internal structure of the collagen network within AC degrades, reducing the structural organization of the tissue.…”

Section: Introductionmentioning

confidence: 99%

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

Kantola,

Karjalainen,

Jaakola

et al. 2024

Magnetic Resonance in Med

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 99%

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

Kantola,

Karjalainen,

Jaakola

et al. 2024

Magnetic Resonance in Med

View full text Add to dashboard Cite

show abstract

Deciphering adiabatic rotating frame relaxometry in biological tissues

Pang

2024

Magnetic Resonance in Med

View full text Add to dashboard Cite

PurposeThis work aims to unravel the intricacies of adiabatic rotating frame relaxometry in biological tissues.Theory and MethodsThe classical formalisms of dipolar relaxation and were systematically analyzed for water molecules reorienting on “fast” and “slow” timescales. These two timescales are, respectively, responsible for the absence and presence of dispersion. A time‐averaged or over an adiabatic pulse duration was recast into a sum of and , but with different weightings. These weightings depend on the specific modulations of adiabatic pulse waveforms. In this context, stretched hyperbolic secant () pulses were characterized. Previously published , continuous‐wave (CW) , and measures from 12 agarose phantoms were used to validate the theoretical predictions. A similar validation was also performed on previously published (=1, 4, 8) and from bovine cartilage specimens.ResultsLongitudinal relaxation weighting decreases for pulses as increases. Predicted CW values from agarose phantoms align well with the measured CW values, as indicated by a linear regression function: . The predicted adiabatic and from cartilage specimens are consistent with those previously measured, as quantified by: .ConclusionThis work has theoretically and experimentally demonstrated that adiabatic and can be recast into a sum of and , with varying weightings. Therefore, any suggestions that adiabatic rotating frame relaxometry in biological tissues could provide more information than the standard and warrant closer scrutiny.

show abstract

The impact of head orientation with respect to B0 on diffusion tensor MRI measures

Kleban,

Jones,

Tax

2023

Imaging Neuroscience

View full text Add to dashboard Cite

Diffusion tensor MRI (DT-MRI) remains the most commonly used approach to characterise white matter (WM) anisotropy. However, DT estimates may be affected by tissue orientation w.r.t. B→0 due to local gradients and intrinsic T2 orientation dependence induced by the microstructure. This work aimed to investigate whether and how diffusion tensor MRI-derived measures depend on the orientation of the head with respect to the static magnetic field, B→0. By simulating WM as two compartments, we demonstrated that compartmental T2 anisotropy can induce the dependence of diffusion tensor measures on the angle between WM fibres and the magnetic field. In in vivo experiments, reduced radial diffusivity and increased axial diffusivity were observed in white matter fibres perpendicular to B→0 compared to those parallel to B→0. Fractional anisotropy varied by up to 20% as a function of the angle between WM fibres and the orientation of the main magnetic field. To conclude, fibre orientation w.r.t. B→0 is responsible for up to 7% variance in diffusion tensor measures across the whole brain white matter from all subjects and head orientations. Fibre orientation w.r.t. B→0 may introduce additional variance in clinical research studies using diffusion tensor imaging, particularly when it is difficult to control for (e.g. fetal or neonatal imaging, or when the trajectories of fibres change due to e.g. space occupying lesions).

show abstract

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

Cited by 3 publications

References 77 publications

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

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

Deciphering adiabatic rotating frame relaxometry in biological tissues

The impact of head orientation with respect to B0 on diffusion tensor MRI measures

Contact Info

Product

Resources

About

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

Cited by 3 publications

References 77 publications

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

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

Deciphering adiabatic rotating frame relaxometry in biological tissues

The impact of head orientation with respect to B0 on diffusion tensor MRI measures

Contact Info

Product

Resources

About

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

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