Functional MR imaging: comparison of BOLD signal intensity changes in fetal organs with fetal and maternal oxyhemoglobin saturation during hypoxia in sheep.
ABSTRACT 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.
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 hypoxic 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 with mean values of control and hypoxic plateaus. BOLD signal intensity was correlated with maternal oxyhemoglobin saturation and fetal oxyhemoglobin saturation; linear regression analysis was performed.
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% CI: 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% CI: 1.58, 1.77) and 1.04% BOLD signal intensity increase per 1% fetal oxyhemoglobin saturation (95% CI: 0.94, 1.13).
BOLD MR imaging can be used to measure changes of oxyhemoglobin saturation in fetal organs during hypoxia. The liver and heart demonstrated the greatest signal intensity decreases during hypoxia.
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ABSTRACT: Mice reproduce many features of human pregnancy and have been widely used to model disorders of pregnancy. However, it has not been known whether fetal mice reproduce the physiologic response to hypoxia known as brain sparing, where blood flow is redistributed to preserve oxygenation of the brain at the expense of other fetal organs. In the present study, blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) and Doppler ultrasound were used to determine the effect of acute hypoxia on the fetal blood flow in healthy, pregnant mice. As the maternal inspired gas mixture was varied between 100% and 8% oxygen on the timescale of minutes, the BOLD signal intensity decreased by 44±18% in the fetal liver and by 12±7% in the fetal brain. Using Doppler ultrasound measurements, mean cerebral blood velocity was observed to rise by 15±8% under hypoxic conditions relative to hyperoxia. These findings are consistent with active regulation of cerebral oxygenation and clearly show brain sparing in fetal mice.Journal of Cerebral Blood Flow & Metabolism advance online publication, 9 April 2014; doi:10.1038/jcbfm.2014.62.Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 04/2014; · 5.46 Impact Factor
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ABSTRACT: Fetal MRI is now a well-established imaging modality for the diagnostic evaluation of fetuses with congenital anomalies. In this article, the authors provide a brief overview of the physical principles involved in fetal MRI imaging, the sequences that are used in clinical practice today, current indications, and limitations. A review of current evidence supports the following indications for fetal MRI: suspected central nervous system anomalies, neck and oropharyngeal masses, diaphragmatic hernia, abdominal masses or bowel pathology not fully characterized by ultrasonography, and suspected fetal infection. Other indications should be decided on a case-by-case basis with close collaboration between the departments of maternal-fetal medicine and radiology. More research is needed to determine the role of fetal MRI in functional neuroimaging at higher magnetic field strengths (3T).Seminars in perinatology 10/2013; 37(5):334-9. · 2.33 Impact Factor
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ABSTRACT: To calculate regional fetal brain oxygen saturation (sO2 ) during hypoxia in sheep. 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 ). 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) /% (r(2) = 0.91). Measured fetal brain BOLD-MRI was compared and converted to pO2 , followed by calculation of cerebral sO2 .J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.Journal of Magnetic Resonance Imaging 12/2013; · 2.57 Impact Factor