Imaging putative foetal cerebral blood oxygenation using susceptibility weighted imaging (SWI)

ObjectiveTo evaluate the magnetic susceptibility, ∆χv, as a surrogate marker of venous blood oxygen saturation, SvO2, in second- and third-trimester normal human foetuses.MethodsThirty-six pregnant women, having a mean gestational age (GA) of 31 2/7 weeks, underwent magnetic resonance imaging (MRI). Susceptibility-weighted imaging (SWI) data from the foetal brain were acquired. ∆χv of the superior sagittal sinus (SSS) was quantified using MR susceptometry from the intra-vascular phase measurements. Assuming the magnetic property of foetal blood, ∆χdo, is the same as that of adult blood, SvO2 was derived from the measured Δχv. The variation of ∆χv and SvO2, as a function of GA, was statistically evaluated.ResultsThe mean ∆χv in the SSS in the second-trimester (n = 8) and third-trimester foetuses (n = 28) was found to be 0.34± 0.06 ppm and 0.49 ±0.05 ppm, respectively. Correspondingly, the derived SvO2 values were 69.4% ±3.27% and 62.6% ±3.25%. Although not statistically significant, an increasing trend (p = 0.08) in Δχv and a decreasing trend (p = 0.22) in SvO2 with respect to advancing gestation was observed.ConclusionWe report cerebral venous blood magnetic susceptibility and putative oxygen saturation in healthy human foetuses. Cerebral oxygen saturation in healthy human foetuses, despite a slight decreasing trend, does not change significantly with advancing gestation.Key points• Cerebral venous magnetic susceptibility and oxygenation in human foetuses can be quantified.• Cerebral venous oxygenation was not different between second- and third-trimester foetuses.• Foetal cerebral venous oxygenation does not change significantly with advancing gestation.