Improved test-retest reliability of R₂* and susceptibility quantification using multi-shot multi-echo 3D EPI

This study aimed to evaluate the potential of 3D EPI for improving the reliability of $T_2^{*}$ -weighted data and quantification of $R_2^{*}$ decay rate and susceptibility (χ) compared with conventional gradient-echo (GRE)-based acquisition.

Eight healthy subjects in a wide age range were recruited. Each subject received repeated scans for both GRE and EPI acquisitions with an isotropic 1 mm resolution at 3 T. Maps of $R_2^{*}$ and χ were quantified, and their interscan differences were used to evaluate the test-retest reliability. Interprotocol differences of $R_2^{*}$ and χ between GRE and EPI were also measured voxel by voxel and in selected regions of interest to test the consistency between the two acquisition methods.

The quantifications of $R_2^{*}$ and χ using EPI protocols showed increased test-retest reliability with higher EPI factors up to 5 as performed in the experiment and were consistent with those based on GRE.

The result suggests that multishot multi-echo 3D EPI can be a useful alternative acquisition method for $T_2^{*}$ -weighted MRI and quantification of $R_2^{*}$ and χ with reduced scan time, improved test-retest reliability, and similar accuracy compared with commonly used 3D GRE.