Quantification of whole-brain oxygenation extraction fraction and cerebral metabolic rate of oxygen consumption in adults with sickle cell anemia using individual T 2 -based oxygenation calibrations.

Purpose: To evaluate different T ₂ -oxygenation calibrations for estimating venous oxygenation in people with sickle cell anemia (SCA).
Methods: Blood T ₂ values were measured at 3 T in the internal jugular veins of 12 healthy volunteers and 11 SCA participants with no history of stroke, recent transfusion, or renal impairment. T ₂ -oxygenation relationships of both sickled and normal blood samples were calibrated individually and compared with values generated from published models. After converting venous T ₂ values to venous oxygenation, whole-brain oxygen extraction fraction and cerebral metabolic rate of oxygen were calculated.
Results: Sickle blood samples' oxygenation values calculated from our individual calibrations agreed well with measurements using a blood analyzer, whereas previous T ₂ calibrations based on normal blood samples showed 13%-19% underestimation. Meanwhile, oxygenation values calculated from previous grouped T ₂ calibration for sickle blood agreed well with experimental measurement on averaged values, but showed up to 20% variation for several individual samples. Using individual T ₂ calibrations, the whole-brain oxygen extraction fraction and cerebral metabolic rate of oxygen of SCA participants were 0.38 ± 0.08 and 172 ± 42 µmol/min/100 g, respectively, which were comparable to those values measured on healthy volunteers.
Conclusion: Our results confirm that sickle blood T ₂ values not only depend on the hematocrit and oxygenation values, but also on other hematological factors. The individual T ₂ calibrations minimized the effect of heterogeneity of sickle blood between different SCA populations and improved the accuracy of T ₂ -based oximetry. The measured oxygen extraction fraction and cerebral metabolic rate of oxygen of this group of SCA participants were found to not differ significantly from those of healthy individuals.
(© 2019 International Society for Magnetic Resonance in Medicine.)