Brain Sparing in Fetal Mice: BOLD MRI and Doppler Ultrasound Show Blood Redistribution During Hypoxia

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.

Functional imaging of the human placenta with magnetic resonance

“…80 OE-MRI is a technique that is very similar to BOLD-MRI, which measures decreases in T1 under oxygen challenge, usually assumed to be due to increases in the partial pressure of dissolved oxygen. 81 Animal studies There are several animal studies on OEand BOLD-MRI in pregnancy, 24,25,30,[82][83][84][85][86] and these techniques may allow detection of abnormal oxygenation or perfusion. Maternal hypoxia in sheep leads …”

Accelerated MRI of the fetal heart using compressed sensing and metric optimized gating

“…The optimum reconstruction from Eq. [2] is one that produces the sparsest images in the transform domain, among all solutions which are consistent with the acquired data. Combining Eqs.…”

Ultrasound-guided spectral photoacoustic imaging of hemoglobin oxygenation during development

“…Though our sample size was too small to demonstrate statistical significance, our calculated sO 2, segmented to the conceptus as shown in the example images, was comparable to expected physiological values-0.44 at E8.5, 0.55 at E14.5, and 0.52 at E16.5. For comparison, placental oxygenation was measured as 0.48 + 0.19 at E14.5 and 0.39 + 0.17 at E17.5 using BOLD MRI [4]. Our spectral analysis algorithms do not correct for wavelength-dependent differences in the optical scattering and absorption in tissues, which change the spectral fluence at depth-future work will implement light scattering and absorption modeling to improve quantification of sO 2 .…”

“…Optical imaging methods that are dependent upon coherent light have limited depth of imaging due to light scattering, while embryonic and fetal tissues provide minimal x-ray contrast [2]; due to these limitations, most optical and x-ray based imaging methods are limited to ex vivo tissue analysis. µMRI provides high resolution images of anatomical structure [3]-in vivo brain sparing has been assessed using blood oxygenation level dependent (BOLD) µMRI [4]. However, real-time measurements are critical for characterization of in vivo function, while clinical applications of MRI during pregnancy are limited due to instrumentation cost and the inability to use the system at bench-side.…”