Prospective motion correction for R2* and susceptibility mapping using spherical navigators

Purpose: To perform prospective motion correction (PMC) for improved R-2* and susceptibility mapping using a purely navigator-based approach. Methods: Spherical navigators (SNAVs) were combined with an additional FID readout for simultaneous measurement of motion and zeroth-order field shifts. The resulting FIDSNAVs were interleaved for PMC of a multi-echo gradient echo sequence with retrospective B-0 correction. Experiments were performed on a 3T scanner with a 32-channel head coil. Performance was assessed in five volunteers with motion prompts derived from real unintentional motion trajectories. Results: At short TEs, PMC alone was sufficient to achieve good image quality; at longer TEs, retrospective B-0 correction was often just as important for artifact reduction as motion correction. Both PMC and retrospective B-0 correction reduced error in R-2* and susceptibility maps for all participants. Residual artifacts were observed in the most severe motion case. Conclusion: Combining SNAVs with an additional FID readout enables simultaneous motion and field correction with no additional hardware requirements, improving the fidelity of quantitative mapping in the presence of motion.