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

Abstract

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 leveldependent 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 DR2∗ and DpO2 was noted (r=0.93, P<0.001), and conversion of pO2 into sO2 resulted in a linear regression coefficient of (-0.1460.01)s-1/% (r2=0.91). Conclusion: Measured fetal brain BOLD-MRI was compared and converted to pO2, followed by calculation of cerebral sO2.