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Towards unconstrained compartment modeling in white matter using diffusion‐relaxation MRI with tensor‐valued diffusion encoding
Author(s) -
Lampinen Björn,
Szczepankiewicz Filip,
Mårtensson Johan,
Westen Danielle,
Hansson Oskar,
Westin CarlFredrik,
Nilsson Markus
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28216
Subject(s) - diffusion mri , white matter , compartment (ship) , isotropy , tensor (intrinsic definition) , diffusion , relaxation (psychology) , nuclear magnetic resonance , chemistry , nuclear medicine , physics , magnetic resonance imaging , mathematics , medicine , neuroscience , geometry , geology , optics , thermodynamics , biology , radiology , oceanography
Purpose To optimize diffusion‐relaxation MRI with tensor‐valued diffusion encoding for precise estimation of compartment‐specific fractions, diffusivities, and T 2 values within a two‐compartment model of white matter, and to explore the approach in vivo. Methods Sampling protocols featuring different b‐values ( b ), b‐tensor shapes ( b Δ ), and echo times (TE) were optimized using Cramér‐Rao lower bounds (CRLB). Whole‐brain data were acquired in children, adults, and elderly with white matter lesions. Compartment fractions, diffusivities, and T 2 values were estimated in a model featuring two microstructural compartments represented by a “stick” and a “zeppelin.” Results Precise parameter estimates were enabled by sampling protocols featuring seven or more “shells” with unique b / b Δ /TE‐combinations. Acquisition times were approximately 15 minutes. In white matter of adults, the “stick” compartment had a fraction of approximately 0.5 and, compared with the “zeppelin” compartment, featured lower isotropic diffusivities (0.6 vs. 1.3 μm 2 /ms) but higher T 2 values (85 vs. 65 ms). Children featured lower “stick” fractions (0.4). White matter lesions exhibited high “zeppelin” isotropic diffusivities (1.7 μm 2 /ms) and T 2 values (150 ms). Conclusions Diffusion‐relaxation MRI with tensor‐valued diffusion encoding expands the set of microstructure parameters that can be precisely estimated and therefore increases their specificity to biological quantities.