Functional MR imaging:: Comparison of BOLD signal intensity changes in fetal organs with fetal and maternal oxyhemoglobin saturation during hypoxia in sheep

Purpose: To compare relative changes in blood oxygen, level-dependent (BOLD) signal intensity in the fetal brain, liver, heart, lungs, and cotyledon with maternal and fetal blood oxygenation during maternal hypoxia in sheep. Materials and Methods: All experimental protocols were reviewed and approved by local, authorities on animal protection. Six anesthetized ewes carrying singleton fetuses underwent magnetic resonance (MR) imaging with rapid single-shot echo-planar imaging BOLD sequence. BOLD imaging of the fetal brain, lungs, liver, heart, and cotyledon was performed during a control phase (ie, normoxia) and a hypoxia phase. Maternal oxyhemoglobin saturation was recorded continuously with pulse oximetry. Fetal blood samples were obtained with a carotid catheter at each phase. Regions of interest were placed in fetal organs. Normalized BOLD signal intensity was calculated plateaus. with mean values of control and hypoxic signal intensity was correlated with maternal oxyhemoglobin saturation and fetal oxyhemoglobin saturation; linear regression analysis was performed. Results: Control maternal and fetal oxyhemoglobin saturation values were 97% (95% confidence interval [CI]: 95%, 100%) and 62% (95% CI: 51%, 73%), respectively. During hypoxia, maternal and fetal oxyhemoglobin saturation values decreased to 75% (95% CI:: 65%. 85%) and 23% (95% Cl: 17%, 29%), respectively. Fetal BOLD signal intensity decreased to 81% (95% CI: 73%. 88%) in the cerebrum, 78% (95% CI: 67%, 89%) in the cerebellum, 83% (95% CI: 80%, 86%) in the lungs, 58% (95% CI: 33%, 84%) in the liver, 53% (95% CI: 43%, 64%) in the heart, and 71% (95% CI: 48%, 94%) in the cotyledon. Correlation of fetal BOLD signal intensity was stronger with fetal (r = 0.91) than with maternal (r = 0.68) oxyhemoglobin saturation; however, the difference was not significant. The highest slope values were obtained for the heart: 1.68% BOLD signal intensity increase per 1% maternal oxyhemoglobin saturation (95% Cl: 1.58, 1.77) and 1.04% BOLD signal intensity increase per 1% fetal oxyhemoglobin saturation (95% Cl: 0.94, 1.13). Conclusion: BOLD MR imaging can be used to measure changes of hypoxia. oxyhemoglobin saturation in fetal organs during by The liver and heart demonstrated the greatest signal intensity decreases during hypoxia.