Non-invasive evaluation of blood oxygen saturation and hematocrit from T1 and T2 relaxation times: In-vitro validation in fetal blood

PurposeWe propose an analytical method for calculating blood hematocrit (Hct) and oxygen saturation (sO(2)) from measurements of its T-1 and T-2 relaxation times. TheoryThrough 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(2) in terms of R-1 and R-2. Resulting solutions for Hct and sO(2) are the roots of cubic polynomials. MethodsFeasibility of the method was established by comparison of Hct and sO(2) 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-1, T-2 measurement uncertainty on precision of Hct and sO(2) estimates. ResultsGood agreement was observed between estimated and ground-truth blood properties (bias=0.01; 95% limits of agreement=0.13 for Hct and sO(2)). Considering the combined effects of biological variability and random measurement noise, we estimate a typical uncertainty of +/- 0.1 for Hct, sO(2) estimates. ConclusionResults demonstrate accurate quantification of Hct and sO(2) from T-1 and T-2. This method is applicable to noninvasive fetal vessel oximetryan application where existing oximetry devices are unusable or require risky blood-sampling procedures. Magn Reson Med 78:2352-2359, 2017. (c) 2017 International Society for Magnetic Resonance in Medicine.