In vivo whole-blood $$$T_2$$$ versus $$$HbO_2$$$ calibration by modulating blood oxygenation level in the femoral vein through intermittent cuff occlusion

The relationship between whole-blood T₂ and blood hemoglobin oxygen saturation (HbO₂) can be modeled as $$${1\over T_{2b}}={1\over T_{2o}}+K(1-HbO_2)^2$$$, where K and T_2o are determined empirically in vitro. The feasibility of estimating K and T_2o in vivo is investigated with T₂-prepared bSSFP at 1.5T in the superficial femoral vein (SFV) with intermittent cuff occlusion. In this manner a range of HbO₂ were achieved allowing quantification of venous oxygen saturation via MR susceptometry, a method that had been validated rigorously against blood gas analysis. Initial result (K=19.6Hz, T_2o=185ms) is lower than the literature value (24.6Hz, 254ms) but not unexpected because transient bSSFP signal is acquired while disturbing the T₂-prepared magnetization.