Resolving partial-volume effects in the brain with multidimensional T1xT2 MRI

Motivation: Despite much work, quantifying relaxation of multiple tissue types within-voxel still evades MRI relaxometry. Goal(s): To compare 2D-T1xT2 spectra against 1D-T1 and 1D-T2 in separating tissue type within-voxel. Approach: The relaxometry spectral fitting methods were compared following in-vivo measurements covering a TExTI grid. Results: The 2D-T1xT2 distributions could better disentangle tissue-types in ground-truth ROIs compared to 1D (T1 or T2) spectra. Voxel-wise fits produced anatomically-meaningful components and volume-fractions. Voxels with multiple spectral peaks (e.g. maximum peaks at typical T1/T2 of gray matter and cerebrospinal fluid) were identified at the appropriate anatomical borderline, suggesting that within-voxel partial-voluming is truly reflected by these peaks. Impact: Resolution limits mean that multiple tissue types are frequently captured within a single MRI voxel. We demonstrate the ability to separate these compartments with 2D-T1xT2 approaches. Measuring multi-dimensional spectra may enable better modelling of the biological sources of MRI contrasts.