Efficient whole-brain tract-specific T mapping at 3T with slice-shuffled inversion-recovery diffusion-weighted imaging.

PURPOSE

Most voxels in white matter contain multiple fiber populations with different orientations and levels of myelination. Conventional T mapping measures 1 T value per voxel, representing a weighted average of the multiple tract T times. Inversion-recovery diffusion-weighted imaging (IR-DWI) allows the T times of multiple tracts in a voxel to be disentangled, but the scan time is prohibitively long. Recently, slice-shuffled IR-DWI implementations have been proposed to significantly reduce scan time. In this work, we demonstrate that we can measure tract-specific T values in the whole brain using simultaneous multi-slice slice-shuffled IR-DWI at 3T.

METHODS

We perform simulations to evaluate the accuracy and precision of our crossing fiber IR-DWI signal model for various fiber parameters. The proposed sequence and signal model are tested in a phantom consisting of crossing asparagus pieces doped with gadolinium to vary T , and in 2 human subjects.

RESULTS

Our simulations show that tract-specific T times can be estimated within 5% of the nominal fiber T values. Tract-specific T values were resolved in subvoxel 2 fiber crossings in the asparagus phantom. Tract-specific T times were resolved in 2 different tract crossings in the human brain where myelination differences have previously been reported; the crossing of the cingulum and genu of the corpus callosum and the crossing of the corticospinal tract and pontine fibers.

CONCLUSION

Whole-brain tract-specific T mapping is feasible using slice-shuffled IR-DWI at 3T. This technique has the potential to improve the microstructural characterization of specific tracts implicated in neurodevelopment, aging, and demyelinating disorders.