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Direction-averaged diffusion-weighted MRI signal using different axisymmetric B-tensor encoding schemes.

Abstract：

PURPOSE:It has been shown, theoretically and in vivo, that using the Stejskal-Tanner pulsed-gradient, or linear tensor encoding (LTE), and in tissue exhibiting a "stick-like" diffusion geometry, the direction-averaged diffusion-weighted MRI signal at high b-values ( 7000 < b < 10000 s / mm 2 ) follows a power-law, decaying as 1 / b . It has also been shown, theoretically, that for planar tensor encoding (PTE), the direction-averaged diffusion-weighted MRI signal decays as 1/b. We aimed to confirm this theoretical prediction in vivo. We then considered the direction-averaged signal for arbitrary b-tensor shapes and different tissue substrates to look for other conditions under which a power-law exists. METHODS:We considered the signal decay for high b-values for encoding geometries ranging from 2-dimensional PTE, through isotropic or spherical tensor encoding to LTE. When a power-law behavior was suggested, this was tested using in silico simulations and, when appropriate, in vivo using ultra-strong (300 mT/m) gradients. RESULTS:Our in vivo results confirmed the predicted 1/b power law for PTE. Moreover, our analysis showed that using an axisymmetric b-tensor a power-law only exists under very specific conditions: (a) "stick-like" tissue geometry and purely LTE or purely PTE waveforms; and (b) "pancake-like" tissue geometry and a purely LTE waveform. CONCLUSIONS:A complete analysis of the power-law dependencies of the diffusion-weighted signal at high b-values has been performed. Only three specific forms of encoding result in a power-law dependency, pure linear and pure PTE when the tissue geometry is "stick-like" and pure LTE when the tissue geometry is "pancake-like". The different exponents of these encodings could be used to provide independent validation of the presence of different tissue geometries in vivo.

journal_name

Magn Reson Med

journal_title

Magnetic resonance in medicine

authors

Afzali M,Aja-Fernández S,Jones DK

doi

10.1002/mrm.28191

subject

Has Abstract

pub_date

2020-09-01 00:00:00

pages

1579-1591

issue

eissn

0740-3194

issn

1522-2594

journal_volume

pub_type

杂志文章

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Direction-averaged diffusion-weighted MRI signal using different axisymmetric B-tensor encoding schemes.