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: The motivation of the project was to investigate the use of oxygen-challenge magnetic resonance imaging (OC-MRI) as a method of diagnosing foetal growth restriction. Foetal growth restriction is associated with restricted foetal oxygen supply and is also associated with increased risks of perinatal mortality and morbidity, and a number of serious and chronic health problems. Measurements of T2* relaxation time, an MRI parameter which increases with blood oxygenation, were made in the right lobe of the foetal liver in 80 singleton pregnancies, before and after the mother breathed oxygen. The groups consisted of 41 foetuses with normal growth and 39 with apparent growth restriction. The mean +/- SD gestational age at scanning was 35 +/- 3 weeks. Changes in foetal liver T2* on maternal oxygen breathing showed no significant difference between the groups therefore the OC-MRI protocol used in this study has no value in the diagnosis of foetal growth restriction. A secondary finding was that a significant positive correlation of T2* change with gestational age was observed. Future studies on the use of oxygen-challenge MRI to investigate foetal growth restriction may therefore need to control for gestational age at the time of MR scanning in order to observe any underlying foetal growth-related effects.Physiological Measurement 09/2010; 31(9):1137-46. · 1.50 Impact Factor
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ABSTRACT: OBJECTIVES: To evaluate whether changes in BOLD signal intensities following hyperoxygenation are related to intrauterine growth restriction (IUGR) in a rat model. METHODS: IUGR was induced in pregnant rats by ligating the left vascular uterine pedicle at day 16 of gestation. BOLD MR imaging using a balanced steady-state free-precession (balanced-SSFP) sequence on a 1.5-T system was performed on day 19. Signal intensities (SI) before and after maternal hyperoxygenation were compared in the maternal liver and in control and growth-restricted foetoplacental units (FPUs). RESULTS: Maternal hyperoxygenation resulted in a significant increase in SI in all regions of interest (P < 0.05) in the 18 rats. In the control group, the SI (mean ± SD) increased by 21 % ± 15 in placentas (n = 74) and 13 % ± 8.5 in foetuses (n = 53). In the IUGR group, the increase was significantly lower: 6.5 % ± 4 in placentas (n = 36) and 7 % ± 5.5 in foetuses (n = 34) (P < 0.05). CONCLUSION: BOLD MRI allows non-invasive assessment of the foetoplacental response to maternal hyperoxygenation in the rat and demonstrates its alteration in an IUGR model. This imaging method may provide a useful adjunct for the early diagnosis, evaluation, and management of human IUGR. KEY POINTS: • Intra-uterine growth restriction is an important cause of perinatal morbidity and mortality. • Blood oxygen level-dependent MRI non-invasively assesses foetoplacental response to maternal hyperoxygenation. • In the rat, foetoplacental response to maternal hyperoxygenation is altered in IUGR. • Functional MRI may help to assess human IUGR.European Radiology 02/2013; · 4.34 Impact Factor