Quantitative BOLD response of the renal medulla to hyperoxic challenge at 1.5 T and 3.0 T

The aim of this study was to gage the magnitude of changes of the apparent renal medullary transverse relaxation time (ΔT 2 *) induced by inhalation of pure oxygen (O 2 ) or carbogen (95% O 2 , 5% CO 2 ) versus baseline breathing of room air. Eight healthy volunteers underwent 2D multi‐gradient echo MR imaging at 1.5 T and 3.0 T. Parametrical T 2 * relaxation time maps were computed and average T 2 * was measured in regions of interest placed in the renal medulla and cortex. The largest T 2 * changes were measured in the renal medulla, with a relative ∆T 2 * of 33.8 ± 22.0% (right medulla) and 34.7 ± 17.6% (left medulla) as compared to room air for oxygen breathing ( p  > 0.01), and 53.8 ± 23.9% and 53.5 ± 33.9% ( p  < 0.01) for carbogen breathing, respectively at 3 T. At 1.5 T, the corresponding values were 13.7 ± 18.5% and 24.1 ± 17.1% ( p  < 0.01) for oxygen breathing and 23.9 ± 17.2% and 38.9 ± 37.6% ( p  < 0.01) for carbogen breathing. As a result, we showed that renal medullary T 2 * times responded strongly to inhalation of hyperoxic gases, which may be attributed to the hypoxic condition of the medulla and subsequent reduction in deoxyhemoglobin. Copyright © 2012 John Wiley & Sons, Ltd.