Human umbilical cord blood relaxation times and susceptibility at 3 T

Purpose: To characterize the magnetic susceptibility and relaxation times (T₁ and T₂ ) of fetal blood at 3 T as a function of the hematocrit (Hct) and oxygen saturation (sO₂ ).

Methods: Susceptibility and relaxometry measurements were performed on cord blood specimens (N = 90, derived from six caesarean deliveries) with a range of hematocrits and oxygen saturations (0.09 < Hct < 0.82, 7 < sO₂ < 100%). To obtain simple, analytic relationships between MRI properties and blood properties, data were fit to established two-compartment (plasma and erythrocytes) models.

Results: Two-compartment models effectively described the cord blood data. The root-mean-squared deviation between the model and the data was 6.3, 10.3, and 1.3% for fits to T₁ , T₂ , and susceptibility measurements. Relaxometry data and estimated T₁ and T₂ model parameters were generally consistent with those reported in cord blood at 1.5 T and comparable to published values for adult blood. Notably, the measured value of Δχ_deo , the susceptibility difference between fully oxygenated (sO₂ = 100%) and deoxygenated (sO₂ = 0) cord blood was approximately 20% lower than the established adult blood value (Δχ_deo,cord = 2.64 ppm, Δχ_deo,adult = 3.4 ppm).

Conclusions: The described models and associated parameter values can be used to inform acquisition parameters, and interpret fetal/neonatal blood susceptibility measurements and relaxometry data acquired at 3 T with respect to hematocrit and sO₂ . Magn Reson Med 79:3194-3206, 2018. © 2017 International Society for Magnetic Resonance in Medicine.