The effect of dissolved oxygen on the relaxation rates of blood plasma: Implications for hyperoxia calibrated BOLD

Purpose To determine the contribution of paramagnetic dissolved oxygen in blood plasma to blood‐oxygenation‐level‐dependent (BOLD) signal changes in hyperoxic calibrated BOLD studies. Methods Bovine blood plasma samples were prepared with partial pressures of oxygen (pO 2 ) ranging from 110 to 600 mmHg. R 1 , R 2 , and R 2 * of the plasma with dissolved oxygen were measured using quantitative MRI sequences at 3 Tesla. Simulations were performed to predict the relative effects of dissolved oxygen and deoxyhemoglobin changes in hyperoxia calibrated BOLD. Results The relaxivities of dissolved oxygen in plasma were found to be r 1, O2 =1.97 ± 0.09 ×10 ‐4 s ‐1 mmHg ‐1 , r 2, O2 =2.3 ± 0.7 ×10 ‐4 s ‐1 mmHg ‐1 , and r 2, O2 * = 2.3 ± 0.7 ×10 ‐4 s ‐1 mmHg ‐1 . Simulations predict that neither the transverse nor longitudinal relaxation rates of dissolved oxygen contribute significantly to the BOLD signal during hyperoxia. Conclusion During hyperoxia, the increases in R 2 and R 2 * of blood from dissolved oxygen in plasma are considerably less than the decreases in R 2 and R 2 * from venous deoxyhemoglobin. R 1 effects due to dissolved oxygen are also predicted to be negligible. As a result, dissolved oxygen in arteries should not contribute significantly to the hyperoxic calibrated BOLD signal. Magn Reson Med 76:1905–1911, 2016. © 2015 International Society for Magnetic Resonance in Medicine