An R2* model of white matter for fiber orientation and myelin concentration

Lee, Jingu; Shin, Hyeong-Geol; Jung, Woojin; Nam, Yoonho; Oh, Se Hong; Lee, Jong-Ho

doi:10.1016/j.neuroimage.2017.08.050

Cited by 25 publications

(63 citation statements)

References 51 publications

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“…We simulated R 2 * (θ) for different iron and myelin concentrations using our numerical model, and fitted Equation to the resulting simulated data. Coefficients c 0 and c 2 were chosen as varying parameters, while c 1 and c 3 were kept fixed at 0.17 and 0.025, respectively, as previously determined . We investigated the behaviour of the myelin‐independent and orientation‐independent coefficient c 0 as a function of the simulated iron concentrations.…”

Section: Theorymentioning

confidence: 62%

“…Lee and colleagues have proposed an empirical model for R 2 * in WM

R_{2}^{*} ((),, θ, MWF) = c_{0} + c_{1} italicMWF + c_{2} italicMWF cos ((), 2 θ) + c_{3} italicMWF cos ((), 4 θ)

where MWF denotes the myelin water fraction, c 0 is a myelin‐independent and orientation‐independent contribution to R 2 * (θ), c 1 is the orientation‐independent contribution of myelin, and c 2 and c 3 are orientation‐dependent contributions of myelin. We simulated R 2 * (θ) for different iron and myelin concentrations using our numerical model, and fitted Equation to the resulting simulated data.…”

Section: Theorymentioning

confidence: 99%

“…Measured R 2 * relaxation in WM depends not only on the tissue composition but also on the angle θ between WM fibre tracts and the main magnetic field B 0 . This orientation dependency has been attributed to the magnetic field inhomogeneities generated by the structural anisotropy of WM tracts and the anisotropic magnetic susceptibility of myelin itself . While DGM structures have the highest iron concentrations of up to 240 mg iron per kg tissue, WM contains about 30 to 45 mg iron per kg of tissue …”

Section: Introductionmentioning

confidence: 99%

“…Consequently, myelin induces a modification on the local magnetic field that depends on the angle between the myelinated axon and the main magnetic field, B 0 . Since iron is predominantly stored in ferritin, a protein shell with an approximately spherical biomineral core, its modifications on the local magnetic field are orientation‐independent . This key difference between myelin sheaths and iron cores opens another avenue for the interrogation of tissue myelin and iron with MRI via the orientation dependency of R 2 * .…”

Section: Introductionmentioning

confidence: 99%

“…By fitting the modelled R 2 * (θ) curves to experimental data, we obtain global averages for iron and myelin contents in non‐lesional WM of patients with MS, healthy siblings of patients, and unrelated healthy controls. The findings obtained from the numerical tissue model are then put into context with a previous R 2 * model . Finally, by acquiring data in an orientation‐independent phantom at varying combinations of diamagnetic bovine serum albumin (BSA) and paramagnetic ferritin concentrations, we explore how these two substances influence R 2 * , albeit in an orientation‐independent manner.…”

Section: Introductionmentioning

confidence: 99%

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The role of iron and myelin in orientation dependent R₂^* of white matter

et al. 2019

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Brain myelin and iron content are important parameters in neurodegenerative diseases such as multiple sclerosis (MS). Both myelin and iron content influence the brain's R2* relaxation rate. However, their quantification based on R2* maps requires a realistic tissue model that can be fitted to the measured data. In structures with low myelin content, such as deep gray matter, R2* shows a linear increase with increasing iron content. In white matter, R2* is not only affected by iron and myelin but also by the orientation of the myelinated axons with respect to the external magnetic field. Here, we propose a numerical model which incorporates iron and myelin, as well as fibre orientation, to simulate R2* decay in white matter. Applying our model to fibre orientation‐dependent in vivo R2* data, we are able to determine a unique solution of myelin and iron content in global white matter. We determine an averaged myelin volume fraction of 16.02 ± 2.07% in non‐lesional white matter of patients with MS, 17.32 ± 2.20% in matched healthy controls, and 18.19 ± 2.98% in healthy siblings of patients with MS. Averaged iron content was 35.6 ± 8.9 mg/kg tissue in patients, 43.1 ± 8.3 mg/kg in controls, and 47.8 ± 8.2 mg/kg in siblings. All differences in iron content between groups were significant, while the difference in myelin content between MS patients and the siblings of MS patients was significant. In conclusion, we demonstrate that a model that combines myelin‐induced orientation‐dependent and iron‐induced orientation‐independent components is able to fit in vivo R2* data.

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Section: Theorymentioning

confidence: 62%

“…Lee and colleagues have proposed an empirical model for R 2 * in WM

R_{2}^{*} ((),, θ, MWF) = c_{0} + c_{1} italicMWF + c_{2} italicMWF cos ((), 2 θ) + c_{3} italicMWF cos ((), 4 θ)

Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The role of iron and myelin in orientation dependent R₂^* of white matter

et al. 2019

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Assessing brain integrity in patients with long‐term and well‐functioning metal‐based hip implants

Taleb,

Varela‐Mattatall,

Allen

et al. 2024

Journal Orthopaedic Research

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Production of metal debris from implant wear and corrosion processes is now a well understood occurrence following hip arthroplasty. Evidence has shown that metal ions can enter the bloodstream and travel to distant organs including the brain, and in extreme cases, can induce sensorial and neurological diseases. Our objective was tosimultaneously analyze brain anatomy and physiology in patients with long‐term and well‐functioning implants. Included were subjects who had received total hip or hip resurfacing arthroplastywith an implantation time of a minimum of 7 years (n = 28) and age‐ and sex‐matched controls (n = 32). Blood samples were obtained to measure ion concentrations of cobalt and chromium, and the Montreal Cognitive Assessment was performed. 3T MRI brain scans were completed with an MPRAGE sequence for ROI segmentation and multiecho gradient echo sequences to generate QSM and R2* maps. Mean QSM and R2* values were recorded for five deep brain and four middle and cortical brain structures on both hemispheres: pallidum, putamen, caudate, amygdala, hippocampus, anterior cingulate, inferior temporal, and cerebellum. No differences in QSM or R2* or cognition scores were found between both groups (p > 0.6654). No correlation was found between susceptibility and blood ion levels for cobalt or chromium in any region of the brain. No correlation was found between blood ion levels and cognition scores. Clinical significance: Results suggest that metal ions released by long‐term and well‐functioning implants do not affect brain integrity.

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