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

Magn Reson Med. 2017 Dec;78(6):2352-2359. doi: 10.1002/mrm.26599. Epub 2017 Feb 12.

Abstract

Purpose: We propose an analytical method for calculating blood hematocrit (Hct) and oxygen saturation (sO2 ) from measurements of its T1 and T2 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 sO2 in terms of R1 and R2 . Resulting solutions for Hct and sO2 are the roots of cubic polynomials.

Methods: Feasibility of the method was established by comparison of Hct and sO2 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 T1 , T2 measurement uncertainty on precision of Hct and sO2 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 sO2 ). Considering the combined effects of biological variability and random measurement noise, we estimate a typical uncertainty of ±0.1 for Hct, sO2 estimates.

Conclusion: Results demonstrate accurate quantification of Hct and sO2 from T1 and T2 . 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.

Keywords: fetal blood; hematocrit; longitudinal relaxation; oxygen saturation; transverse relaxation.

MeSH terms

  • Female
  • Fetal Blood / diagnostic imaging*
  • Hematocrit*
  • Humans
  • Magnetic Resonance Imaging*
  • Models, Theoretical
  • Monte Carlo Method
  • Oximetry*
  • Oxygen / chemistry*
  • Placenta / diagnostic imaging
  • Pregnancy
  • Reproducibility of Results
  • Umbilical Cord / diagnostic imaging

Substances

  • Oxygen