BOLD MRI in the brain of fetal sheep at 3T during experimental hypoxia.

Purpose To calculate regional fetal brain oxygen saturation (sO2) during hypoxia in sheep. Materials and Methods Eight pregnant ewes were examined at a 3T MR-scanner using blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) to measure signal intensity changes of the fetal brain during a control period and a period of induced hypoxia. Regions of interest were placed in the fetal cerebrum to assess ΔR2* from GRE signal intensity plateaus (Scontrol, Shypoxia) and the relation between ΔR2* and ΔpO2 was analyzed. A probe was placed surgically in the fetal brain to directly measure local pO2 as a reference standard. Baseline and hypoxic pO2 values were recorded and compared (ΔpO2). Results Mean fetal brain pO2 decreased from 14.3 mmHg (95% confidence interval [CI]: 10–19) to 3.4 mmHg (95% CI: 2–5) during hypoxia (mean ΔpO2 = 10.9 mmHg and ΔR2* = −5s−1). A significant correlation between ΔR2* and ΔpO2 was noted (r = 0.93, P < 0.001), and conversion of pO2 into sO2 resulted in a linear regression coefficient of (−0.14 ± 0.01)s−1/% (r2 = 0.91). Conclusion Measured fetal brain BOLD-MRI was compared and converted to pO2, followed by calculation of cerebral sO2. J. Magn. Reson. Imaging 2015;41:110–116. © 2013 Wiley Periodicals, Inc.