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.
[Show abstract][Hide abstract] ABSTRACT: Blood-oxygenation-level-dependent functional magnetic resonance imaging is a noninvasive technique that has become increasingly popular in the neurosciences. It measures the proportion of oxygenated haemoglobin in specific areas of the brain, mirroring blood flow and therefore function. Here we review how the findings from functional studies impact on areas of gynaecological practice as diverse as chronic pain, continence, and premenstrual dysphoric disorder. Finally we review some of the more novel applications of the technique, such as imaging of pelvic floor function and the effects of hypoxia on the fetus.
BJOG An International Journal of Obstetrics & Gynaecology 02/2009; 116(2):240-6. DOI:10.1111/j.1471-0528.2008.01993.x · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ultrasound (US) is the imaging method of choice before 20 weeks of gestation, as screening modality, where repeated examinations
are required and where magnetic resonance imaging (MRI) is contraindicated or has failed. In the right hands, US appears to
be the equal of MRI in most instances of fetal cerebral pathology. MRI is preferred where US would be expected to be difficult,
such as a very obese patient and in instances where acute asphyxia or cerebral tuberous sclerosis is suspected. A combination
of US and MRI is preferred for possible fetal central nervous system complications related to congenital cytomegaloviral infection,
trauma, bleeding, tumors, or cerebellar bleeding or telangiectasia. Whichever modality is used, the final diagnosis of complex
central nervous system pathology should be made in a multidisciplinary setting.
[Show abstract][Hide abstract] ABSTRACT: This work reports on the existence of deterministic nonlinear dynamics in a free-running multimode semiconductor laser. The main dynamical effects found in a set of experiments realized with several edge-emitting lasers are: (i) periodic fluctuations, in the MHz range, of each modal output, (ii) compensation in the total output which remains practically flat, (iii) the modal switching sequence follows the modal optical frequencies sequence from blue to red; when the reddest mode switches off, the sequence restarts from the bluest mode. These effects are robust against a change of the control parameters which mostly affects the number of oscillating modes. Experimentally, the pump current of the lasers was increased and it was verified that the property of regular modal switching with flat total output is independent of the mode number, up to seven oscillating modes. For large number of modes, the fluctuations persist but they can lose regularity in phase and amplitude. The authors have always noticed the almost complete extinction (more than -40 dB) of the modal switching frequency in the total intensity and the switching sequence that progresses from the blue side of the optical spectrum to the red side. The frequency of the modal switching tends to increase with pumping current and with the number of active modes but it remains in the range 5 to 15 MHz. No significant difference between the power spectra of the different modal amplitudes was observed.
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