Comparison of normal tissue R1 and R*2 modulation by oxygen and carbogen

Magnetic resonance imaging has shown promise for evaluating tissue oxygenation. In this study differences in the tissue longitudinal relaxation rate (R1) and effective transverse relaxation rate (R*2), induced by inhalation of pure oxygen and carbogen, were evaluated in 10 healthy subjects. Significant reductions in R1 were demonstrated following both oxygen and carbogen inhalation in the spleen (both P <0.001), liver (P = 0.002 air vs. oxygen; P = 0.001 air vs. carbogen), skeletal muscle (both P <0.001), and renal cortex (P = 0.005 air vs. oxygen; P = 0.008 air vs. carbogen). No significant change in R* 2occurred following pure oxygen in any organ. However, a significant increase in R*2was observed in the spleen (P <0.001), liver (P = 0.001), skeletal muscle (P = 0.026), and renal cortex (P = 0.001) following carbogen inhalation, an opposite effect to that observed in many studies of tumor pathophysiology. Changes in R1 and R*2were independent of the gas administration order in the spleen and skeletal muscle. These findings suggest that the R1 and R*2 responses to hyperoxic gases are independent biomarkers of oxygen physiology. © 2008 Wiley-Liss, Inc.