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

Abstract

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 (pO2) ranging from 110 to 600 mmHg. R1, R2, and R2* 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 r1,O2 =1.97 ± 0.09 ×10-4 s-1mmHg-1, r2,O2 =2.3 ± 0.7 ×10-4 s-1mmHg-1, and r2,O2* = 2.3 ± 0.7 ×10-4 s-1mmHg-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 R2 and R2* of blood from dissolved oxygen in plasma are considerably less than the decreases in R2 and R2* from venous deoxyhemoglobin. R1 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.