Introduction: Blood transfusion for primary stroke prevention is well established in children but not adults with sickle cell anemia (SCA). Secondary stroke prevention in young adults with SCA is generally accepted. However blood transfusion therapy does not prevent all infarcts and recurrent assessment of cerebral physiology is likely necessary to portend stroke risk.
Hypothesis: Oxygen extraction fraction (OEF), which reflects the balance of oxygen consumed to oxygen delivered, can be evaluated routinely noninvasively in vivo using MRI and reduces following blood transfusion; if confirmed, routine MRI-based OEF screening could be applied to evaluate impact of blood transfusion and other therapies on tissue-level impairment.
Methods: The noninvasive T2-relaxation-under-spin-tagging (TRUST)-MRI method (duration=1min12s) was applied in adults with SCA (n=5) and age and race-matched control (n=11) volunteers. SCA volunteers were scanned pre- and post-transfusion and controls at two time points to assess healthy OEF reproducibility and hypothesized changes after transfusion, respectively. OEF changes were contrasted with symptoms, vasculopathy, and perfusion. A Kruskal-Wallis test with two-sided p<0.05 was used to evaluate significant differences.
Results: In adults with SCA, mean age 33±3 years (y) OEF was significantly elevated (p<0.01, OEF=0.53±0.09) relative to controls (mean age 27±5y, OEF=0.32±0.06). OEF was not significantly different at follow-up for controls (OEF=0.33±0.05), but was reduced (OEF=0.44±0.05; p=0.021) following transfusion in SCA volunteers (Figure). Reduction in OEF is inversely correlated with increase in hematocrit post-transfusion.
Conclusion: Noninvasive MRI can quickly detect expected reductions in OEF after blood transfusion. Ongoing work is focused on understanding relationships between OEF, changes in symptomatology and stroke risk in SCA. OEF has been predictive of stroke risk in other patient groups.