Self‐Correction of B 0 Drift and Trajectory Error in Alternating Unbalanced SSFP ‐ FID and SSFP ‐ ECHO ( AUSFIDE )‐Based 3D Transverse Relaxometry of the Human Brain

Purpose The alternating unbalanced SSFP (AUSFIDE) pulse sequence, which consists of multi‐echo trains of SSFP‐FID and SSFP‐ECHO modules, enables rapid estimation of R 2 and R 2 ′, but is prone to errors from temporal drift of the main magnetic field ( B 0 ) and k ‐space trajectory mismatch. Here, we propose a self‐correcting AUSFIDE method for joint correction of these two sources of error without requiring additional scans. Methods AUSFIDE signals were modeled in the presence of B 0 drift and k ‐space shifts. To estimate and correct for B 0 drift over the entire scan, phase navigators without spatial encoding were inserted before and after each multi‐echo train. In addition, the intrinsic phase symmetry between SSFP‐FID and SSFP‐ECHO signals was exploited, enabling self‐calibration of the k ‐space sampling trajectory. Numerical simulations and phantom experiments were performed for proof‐of‐concept validation, followed by in vivo brain imaging of 10 healthy subjects on two 3 T scanners. Measured parameters were analyzed in six brain regions, and test–retest reproducibility was evaluated on the two MRI platforms. Results Simulations and phantom imaging consistently demonstrated that B 0 drift and trajectory errors resulted in image distortions and heavily overestimated R 2 ′. Experiments further revealed that these artifacts and quantification errors were substantially reduced by the proposed self‐correction method. Inter‐scan agreement of the quantified parameters was also improved after correction on both scanners. Conclusion The self‐corrected AUSFIDE method is able to compensate for errors from B 0 drift and k ‐space trajectory mismatch, and thus is a potentially practical and reliable means for 3D transverse relaxometry.