Real-time fetal brain and placental T2* mapping at 0.55T MRI.

Purpose: To provide real-time, organ-specific quantitative information - specifically placental and fetal brain T2 * - to optimize and personalize fetal MRI examinations.

Methods: A low-latency setup enables real-time processing, including segmentation, T2* fitting, and centile calculation. Two nnU-Nets were trained on 2 989 fetal brains, and 540 placental datasets for automatic segmentation. Normative T2* curves over gestation were derived from 88 healthy cases. Prospective testing included 50 fetal MRI scans: A validation cohort (10 exams with three intra-scan repetitions) and an evaluation cohort (40 participants). Validation was performed with Bland-Altman assessments and Dice coefficients between repetitions, manual/automatic segmentations, and online/offline quantification.

Results: T2* maps and centiles for the fetal brain and placenta were available in under one minute for all cases. The validation cohort showed robust reproducibility, with intra-scan mean T2* differences of 1.04, -3.17, and 5.07 ms for the fetal brain and -3.15, 4.74, and 2.45 ms for the placenta. Mean T2* differences between online and offline processing were 1.63 ms and 0.16 ms for the fetal brain and placenta, respectively. Dice coefficients were for the placenta and for the fetal brain.

Conclusions: Real-time quantitative imaging supports personalized MR exams, optimizing sequence selection and working towards reducing recall rates. The ability to assess T2*, a potential biomarker for pregnancy complications, in real-time opens new clinical possibilities. Future research will apply this pipeline to pregnancies affected by preeclampsia and growth restriction and explore MR-guided fetal interventions.