Searching for the neurite density with diffusion MRI: Challenges for biophysical modeling
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Searching for the neurite density with diffusion MRI: Challenges for biophysical modeling. / Lampinen, Björn; Szczepankiewicz, Filip; Novén, Mikael; van Westen, Danielle; Hansson, Oskar; Englund, Elisabet; Mårtensson, Johan; Westin, Carl-Fredrik; Nilsson, Markus.
In: Human Brain Mapping, Vol. 40, No. 8, 2019, p. 2529-2545.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Searching for the neurite density with diffusion MRI: Challenges for biophysical modeling
AU - Lampinen, Björn
AU - Szczepankiewicz, Filip
AU - Novén, Mikael
AU - van Westen, Danielle
AU - Hansson, Oskar
AU - Englund, Elisabet
AU - Mårtensson, Johan
AU - Westin, Carl-Fredrik
AU - Nilsson, Markus
N1 - Publisher Copyright: © 2019 The Authors. Human Brain Mapping published by Wiley Periodicals, Inc.
PY - 2019
Y1 - 2019
N2 - In vivo mapping of the neurite density with diffusion MRI (dMRI) is a high but challenging aim. First, it is unknown whether all neurites exhibit completely anisotropic (“stick-like”) diffusion. Second, the “density” of tissue components may be confounded by non-diffusion properties such as T2 relaxation. Third, the domain of validity for the estimated parameters to serve as indices of neurite density is incompletely explored. We investigated these challenges by acquiring data with “b-tensor encoding” and multiple echo times in brain regions with low orientation coherence and in white matter lesions. Results showed that microscopic anisotropy from b-tensor data is associated with myelinated axons but not with dendrites. Furthermore, b-tensor data together with data acquired for multiple echo times showed that unbiased density estimates in white matter lesions require data-driven estimates of compartment-specific T2 values. Finally, the “stick” fractions of different biophysical models could generally not serve as neurite density indices across the healthy brain and white matter lesions, where outcomes of comparisons depended on the choice of constraints. In particular, constraining compartment-specific T2 values was ambiguous in the healthy brain and had a large impact on estimated values. In summary, estimating neurite density generally requires accounting for different diffusion and/or T2 properties between axons and dendrites. Constrained “index” parameters could be valid within limited domains that should be delineated by future studies.
AB - In vivo mapping of the neurite density with diffusion MRI (dMRI) is a high but challenging aim. First, it is unknown whether all neurites exhibit completely anisotropic (“stick-like”) diffusion. Second, the “density” of tissue components may be confounded by non-diffusion properties such as T2 relaxation. Third, the domain of validity for the estimated parameters to serve as indices of neurite density is incompletely explored. We investigated these challenges by acquiring data with “b-tensor encoding” and multiple echo times in brain regions with low orientation coherence and in white matter lesions. Results showed that microscopic anisotropy from b-tensor data is associated with myelinated axons but not with dendrites. Furthermore, b-tensor data together with data acquired for multiple echo times showed that unbiased density estimates in white matter lesions require data-driven estimates of compartment-specific T2 values. Finally, the “stick” fractions of different biophysical models could generally not serve as neurite density indices across the healthy brain and white matter lesions, where outcomes of comparisons depended on the choice of constraints. In particular, constraining compartment-specific T2 values was ambiguous in the healthy brain and had a large impact on estimated values. In summary, estimating neurite density generally requires accounting for different diffusion and/or T2 properties between axons and dendrites. Constrained “index” parameters could be valid within limited domains that should be delineated by future studies.
KW - Anisotropy
KW - Axons
KW - Dendrites
KW - Diffusion MRI
KW - Myelin
KW - Neurites
U2 - 10.1002/hbm.24542
DO - 10.1002/hbm.24542
M3 - Journal article
C2 - 30802367
AN - SCOPUS:85062351656
VL - 40
SP - 2529
EP - 2545
JO - Human Brain Mapping
JF - Human Brain Mapping
SN - 1065-9471
IS - 8
ER -
ID: 305547946