Breathing hyperoxic gas results in dissolved oxygen in blood plasma, shortening T1 of arterial blood (T1a). Quantification of T1a is difficult due to blood flow between the inversion and acquisition. Here, this problem is overcome using an intermittent cuff occlusion protocol to suspend flow in the femoral artery and vein. An inversion recovery-prepared bSSFP sequence was used to measure T1a during normoxia (FiO2=21% O2) and graded hyperoxia (FiO2~33%, 48%, 55%, 100% O2) in ten healthy subjects at 3T. During normoxia, T1a was 1819±142ms, which was shortened to 1522±100ms during maximal hyperoxia, and the relationship between T1a and PETO2 was linear.