Possibilities of T2*-Relaxometry and Diffusion-Weighted MRI for Fetal Brain and Placental Assessment

Hypoxia is one of the leading causes of impaired intrauterine development and adverse perinatal outcomes. The T2*-relaxometry method, based on the BOLD effect, enables noninvasive quantitative assessment of tissue oxygenation. Apparent diffusion coefficient (ADC) mapping is employed in the diagnosis of cerebral ischemia and serves as a quantitative biomarker of prenatal brain maturation. Objective . To compare the utility of T2*-relaxometry and ADC mapping in assessing gestational characteristics, as well as hypoxic conditions of the fetal brain and placenta. Materials and Methods . A retrospective cross-sectional analysis was conducted on 200 prenatal MRI examinations performed between 18 and 38 weeks of gestation (WG) from 2024 to 2025, using 1.5 T and 3 T Philips scanners at the MTC SB RAS (Novosibirsk, Russia). T2*- relaxometry was performed using a multi-echo single-shot echo-planar imaging (SS-EPI) sequence with TE ranging from 25 to 225 ms. ADC mapping was conducted using single-shot diffusion-weighted imaging (SSh DWI) with b-values of 0 and 700 s/mm². T2*-relaxation times (RT) and ADC values were obtained through ROI analysis of manually segmented regions of the brain and placenta. Statistical analysis included the Shapiro — Wilk test, Pearson and Spearman correlations, paired t-test, ANOVA, and Kruskal — Wallis test, with significance set at p < 0.05. Results . T2*-mapping of the brain in 110 fetuses (66 scanned at 1.5 T; 44 at 3 T) and of the placenta in 50 cases (30 at 1.5 T; 20 at 3 T) demonstrated a decrease in T2*-RT with advancing gestational age (p = 0.0018 for the brain, p = 0.05 for the placenta). ADC values of the fetal brain (n = 126) were also inversely correlated with gestational age (p = 0.0135), whereas no significant gestational dependence was found for placental T2*-RT or ADC values (p > 0.209). Group analysis revealed a significant reduction in fetal brain T2*-RT after 29 WG compared to fetuses before 29 WG (p = 0.001). Conclusions . Both T2*-RT and ADC values of the fetal brain are significantly influenced by gestational age, with more pronounced changes observed in the third trimester. T2*-relaxometry and ADC mapping are applicable for quantitative evaluation of fetal brain and placental deve- lopment and hold potential for early, noninvasive detection of hypoxic conditions.