2018/06/07 by Björn Lampinen, Lampinen, Björn, Filip Szczepankiewicz +15 · 2 citations
Medicine · #Advanced Neuroimaging Techniques and Applications #Bone and Joint Diseases #FOS: Physical sciences #MRI in cancer diagnosis #Medical Physics (physics.med-ph)
paper · pdf · doi:10.48550/arxiv.1806.02731
openalex publication_date 2018/06/07 · openalex created_date 2023/02/16 · openalex updated_date 2026/07/28
In vivo mapping of the neurite density with diffusion MRI (dMRI) is a high\nbut challenging aim. First, it is unknown whether all neurites exhibit\ncompletely anisotropic ('stick-like') diffusion. Second, the 'density' of\ntissue components may be confounded by non-diffusion properties such as T2\nrelaxation. Third, the domain of validity for the estimated parameters to serve\nas indices of neurite density is incompletely explored. We investigated these\nchallenges by acquiring data with 'b-tensor encoding' and multiple echo times\nin both healthy brain and white matter lesions. Results showed that microscopic\nanisotropy from b-tensor data is associated with myelinated axons but not with\ndendrites. Furthermore, b-tensor and multi-echo data showed that unbiased\ndensity estimates in white matter lesions require data-driven estimates of\ncompartment-specific T2 times. Finally, the 'stick' fractions of different\nbiophysical models could generally not serve as neurite density indices across\nthe healthy brain and white matter lesions, where outcomes of comparisons\ndepended on the choice of constraints. In particular, constraining\ncompartment-specific T2 times was ambiguous in the healthy brain and had a\nlarge impact on estimated values. In summary, estimating neurite density may\nrequire accounting for different diffusion and/or T2 properties between axons\nand dendrites. Constrained 'index' parameters could be valid within limited\ndomains that should be delineated by future studies.\n