Premium
A continuum of T 2 * components: Flexible fast fraction mapping in sodium MRI
Author(s) -
Syeda Warda,
Blunck Yasmin,
Kolbe Scott,
Cleary Jon O.,
Johnston Leigh A.
Publication year - 2019
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.27659
Subject(s) - imaging phantom , biological system , weighting , exponential function , exponential decay , estimation theory , statistical physics , physics , nuclear magnetic resonance , mathematics , algorithm , mathematical analysis , optics , acoustics , nuclear physics , biology
Purpose Parameter mapping in sodium MRI data is challenging due to inherently low SNR and spatial resolution, prompting the need to employ robust models and estimation techniques. This work aims to develop a continuum model of sodium T 2 * ‐decay to overcome the limitations of the commonly employed bi‐exponential models. Estimates of mean T 2 * ‐decay and fast component fraction in tissue are emergent from the inferred continuum model. Methods A closed‐form continuum model was derived assuming a gamma distribution of T 2 * components. Sodium MRI was performed on four healthy human subjects and a phantom consisting of closely packed vials filled with an aqueous solution of varying sodium and agarose concentrations. The continuum model was applied to the phantom and in vivo human multi‐echo 7T data. Parameter maps by voxelwise model‐fitting were obtained. Results The continuum model demonstrated comparable estimation performance to the bi‐exponential model. The parameter maps provided improved contrast between tissue structures. The fast component fraction, an indicator of the heterogeneity of localised sodium motion regimes in tissue, was zero in CSF and high in WM structures. Conclusions The continuum distribution model provides high quality, high contrast parameter maps, and informative voxelwise estimates of the relative weighting between fast and slow decay components.