title: Dependence of blood T(2) on oxygenation at 7 T: in vitro calibration and in vivo application.
abstract: OBJECTIVE
  The calibratable relationship between blood oxygenation (Y) and T(2) allows quantification of cerebral venous oxygenation. We aim to establish a calibration plot between blood T(2) , Y, and hematocrit at 7 T, and using T(2) -relaxation-under-spin-tagging MRI, determine human venous blood oxygenation in vivo.
  
  
  METHODS
  In vitro experiments were performed at 7 T on bovine blood samples using a Carr-Purcell-Meiboom-Gill-T2 sequence, from which we characterized the relationship among T(2) , Y, and hematocrit. T(2) -relaxation-under-spin-tagging MRI was implemented at 7 T to measure venous blood T2 in vivo, from which oxygenation was estimated using the in vitro calibration plot. Hyperoxia was performed to test the sensitivity of the method to oxygenation changes, and the 7 T results were compared with those at 3 T.
  
  
  RESULTS
  In vitro data showed that arterial and venous T(2) at 7 T are 68 and 20 ms, respectively, at a typical hematocrit of 0.42. In vivo measurement showed a cerebral venous oxygenation of 64.7 ± 5.0% and a test-retest coefficient-of-variation of 3.6 ± 2.4%. Hyperoxia increased Yv by 9.0 ± 1.4% (P = 0.001) and the 3 and 7 T results showed a strong correlation (R = 0.95) across individuals.
  
  
  CONCLUSIONS
  We provided an in vitro calibration plot for conversion of blood T(2) to oxygenation at 7 T and demonstrated its utility in vivo.
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Department of Biomedical Engineering, University of Texas at Arlington, Arlington, Texas, USA.
authors.forename: Lisa C
authors.initials: LC
authors.lastname: Krishnamurthy
authors.forename: Peiying
authors.initials: P
authors.lastname: Liu
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
authors.forename: Jinsoo
authors.initials: J
authors.lastname: Uh
authors.forename: Ivan
authors.initials: I
authors.lastname: Dimitrov
authors.forename: Hanzhang
authors.initials: H
authors.lastname: Lu
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000502:physiology; D002138:Calibration; D002417:Cattle; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D010100:Oxygen
keywords: 7 T; TRUST; blood T2; blood oxygen saturation; brain