C-FLAIR: Fluid-attenuated Inversion Recovery with Controlled Artifact Suppression in Brain MRI

Background The T2-weighted fluid-attenuated inversion recovery (FLAIR) sequence is part of the routine brain MRI protocol. In regions with strong inhomogeneities in the static magnetic (B₀) field and/or the radiofrequency (RF) field, inadequate magnetization inversion results in artifacts that may mimic or obscure pathologic features. Purpose To reduce artifacts on FLAIR images by using an optimized inversion pulse that is robust to inhomogeneities in both the B₀ and RF fields. Materials and Methods In this prospective study, a FLAIR inversion pulse was designed using optimal control. FLAIR and FLAIR with controlled inversion (C-FLAIR) images were acquired at 3 T in a phantom designed to exhibit strong inhomogeneities in B₀ and in 14 participants (mean age, 36.1 years ± 11.5 [SD]; nine male participants) enrolled between October 2024 and August 2025 at a single academic medical center: nine healthy participants, two with relapsing-remitting multiple sclerosis, one with persistent concussion symptoms, and two with asymptomatic white matter hyperintensities. In the phantom, water signal suppression was assessed visually. In human participants, cerebrospinal fluid signal suppression, presence of artifacts, and visibility of multiple sclerosis lesions and white matter hyperintensities were assessed visually by a radiologist. In eight healthy volunteers, mean signal-to-noise ratio (SNR) and mean contrast-to-noise ratio (CNR) were computed for FLAIR and C-FLAIR, with differences between the sequences evaluated using the Student <i>t</i> test. Results C-FLAIR exhibited nearly perfect inversion in the presence of inhomogeneities in the B₀ field, resulting in the removal of artifactual signal. The image contrast of demyelinating multiple sclerosis lesions and white matter hyperintensities was identical for the optimized pulse and the conventional pulse. There was no evidence of a difference in mean SNR (26.5 ± 3.5 for FLAIR vs 26.4 ± 4.7 for C-FLAIR) or mean CNR (18.5 ± 2.1 for FLAIR vs 17.9 ± 2.4 for C-FLAIR) between sequences. C-FLAIR had 13.8% higher specific absorption rate (0.033 vs 0.029 W/kg) and 6.8% higher time-averaged RF (0.78 vs 0.73 µT). Conclusion C-FLAIR with robust RF inversion showed practical elimination of artifacts caused by incomplete inversion. © RSNA, 2025 See also the editorial by Casselman and Bowen in this issue.