Non-invasive evaluation of blood oxygen saturation and hematocrit from T and T relaxation times: In-vitro validation in fetal blood.

Purpose: We propose an analytical method for calculating blood hematocrit (Hct) and oxygen saturation (sO ) from measurements of its T and T relaxation times.

Theory: Through algebraic substitution, established two-compartment relationships describing R1=T1-1 and R2=T2-1 as a function of hematocrit and oxygen saturation were rearranged to solve for Hct and sO in terms of R and R . Resulting solutions for Hct and sO are the roots of cubic polynomials.

Methods: Feasibility of the method was established by comparison of Hct and sO estimates obtained from relaxometry measurements (at 1.5 Tesla) in cord blood specimens to ground-truth values obtained by blood gas analysis. Monte Carlo simulations were also conducted to assess the effect of T , T measurement uncertainty on precision of Hct and sO estimates.

Results: Good agreement was observed between estimated and ground-truth blood properties (bias = 0.01; 95% limits of agreement = ±0.13 for Hct and sO ). Considering the combined effects of biological variability and random measurement noise, we estimate a typical uncertainty of ±0.1 for Hct, sO estimates.

Conclusion: Results demonstrate accurate quantification of Hct and sO from T and T . This method is applicable to noninvasive fetal vessel oximetry-an application where existing oximetry devices are unusable or require risky blood-sampling procedures. Magn Reson Med 78:2352-2359, 2017. © 2017 International Society for Magnetic Resonance in Medicine.