Free water elimination diffusion tractography: A comparison with conventional and fluid-attenuated inversion recovery, diffusion tensor imaging acquisitions.

Abstract

White matter tractography reconstructions using conventional diffusion tensor imaging (DTI) near cerebrospinal fluid (CSF) spaces are often adversely affected by CSF partial volume effects (PVEs). This study evaluates the ability of free water elimination (FWE) DTI methods to minimize the PVE of CSF for deterministic tractography applications. Ten healthy individuals were scanned with "traditional," FLAIR (fluid-attenuated inversion recovery), and FWE DTI scans. The fornix, corpus callosum, and cingulum bundles were reconstructed using deterministic tractography. The FWE DTI scan was performed twice to separately match total acquisition time (long FWE) and number of measurements (encoding directions, short FWE) to the FLAIR and "traditional" DTI scans. PVE resolution was determined based on reconstructed tract volume. All reconstructions underwent blinded review for anatomical correctness, symmetry, and completeness. Reconstructions of the fornix demonstrated that the FWE and FLAIR scans produce more complete, anatomically plausible reconstructions than "traditional" DTI. Additionally, the tract reconstructions using FWE-DTI were significantly larger than when FLAIR was used with DTI (P < 0.0005). FLAIR and the FWE methods led to signal-to-noise ratio (SNR) reductions of 33% and 11%, respectively, compared with conventional DTI. The long and short FWE acquisitions did not significantly (P ≥ 0.31) differ from one another for any of the reconstructed tracts. The FWE diffusion model overcomes CSF PVE without the time, SNR, and volumetric coverage penalties inherent to FLAIR DTI.