R₁ and R₂* changes in the human placenta in response to maternal oxygen challenge

PURPOSE: Pregnancy complications such as preeclampsia and fetal growth restriction are sometimes thought to be caused by placental abnormalities associated with reduced oxygenation. Oxygen-enhanced MRI (R1 contrast) and BOLD MRI (R2 * contrast) have the potential to noninvasively investigate this oxygen environment at a range of gestational ages. METHODS: Scanning was carried out at 1.5 T under maternal air and oxygen breathing in a single placental slice in 14 healthy pregnant subjects of gestational ages 21-37 weeks. We report R1 changes using a respiratory-triggered inversion recovery-turbo spin-echo sequence, which is sensitive to changes in PO2 , and R2 * changes using a breathhold multiple gradient-recalled echo sequence sensitive to changes in oxygen saturation. RESULTS: Significant R1 increases (P < 0.005, paired t-test) and R2 * decreases (P < 0.0001, paired t-test) between air and oxygen breathing were demonstrated. ΔR1 decreased with gestational age (P < 0.0005, r = -0.835, Pearson correlation test). No significant effect of gestational age on R2 * change was observed. CONCLUSION: The results demonstrate the feasibility of non-invasive investigation of placental oxygenation using MRI and the sensitivity of R1 oxygen-enhanced MRI to gestational age. The techniques have the potential to provide unique noninvasive biomarkers in compromised pregnancies.