title: Non-invasive evaluation of blood oxygen saturation and hematocrit from T1and T2relaxation times: In-vitro validation in fetal blood.
abstract: OBJECTIVE
  We propose an analytical method for calculating blood hematocrit (Hct) and oxygen saturation (sO2) from measurements of its T1and T2relaxation times.
  
  
  BACKGROUND
  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 sO2in terms of R1and R2. Resulting solutions for Hct and sO2are the roots of cubic polynomials.
  
  
  METHODS
  Feasibility of the method was established by comparison of Hct and sO2estimates 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, T2measurement uncertainty on precision of Hct and sO2estimates.
  
  
  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, sO2estimates.
  
  
  CONCLUSIONS
  Results demonstrate accurate quantification of Hct and sO2from T1and 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.
authors.affiliation: University of Toronto, Department of Medical Biophysics, Toronto, Canada.|Mouse Imaging Centre, Hospital for Sick Children, Toronto, Canada.
authors.forename: Sharon
authors.initials: S
authors.lastname: Portnoy
authors.affiliation: Hospital for Sick Children, Division of Cardiology, Toronto, Canada.|University of Toronto, Department of Pediatrics and Diagnostic Imaging, Toronto, Canada.
authors.forename: Mike
authors.initials: M
authors.lastname: Seed
authors.affiliation: University of Toronto, Department of Medical Biophysics, Toronto, Canada.|Mouse Imaging Centre, Hospital for Sick Children, Toronto, Canada.|University of Toronto, Department of Obstetrics and Gynecology, Toronto, Canada.
authors.forename: John G
authors.initials: JG
authors.lastname: Sled
authors.affiliation: University of Toronto, Department of Medical Biophysics, Toronto, Canada.|Hospital for Sick Children, Department of Physiology and Experimental Medicine, Toronto, Canada.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Macgowan
mesh_terms: D005260:Female; D005312:Fetal Blood / Q000000981:diagnostic imaging*; D006400:Hematocrit; D006801:Humans; D008279:Magnetic Resonance Imaging; D008962:Models, Theoretical; D009010:Monte Carlo Method; D010092:Oximetry; D010100:Oxygen / Q000737:chemistry*; D010920:Placenta / Q000000981:diagnostic imaging; D011247:Pregnancy; D015203:Reproducibility of Results; D014470:Umbilical Cord / Q000000981:diagnostic imaging
chemical_list: D010100:Oxygen
keywords: fetal blood; hematocrit; longitudinal relaxation; oxygen saturation; transverse relaxation