Influence of oxygen and carbogen breathing on renal oxygenation measured by T2*-weighted imaging at 3.0 T.

The aim of the study was to assess the influence of carbogen (95% O(2), 5% CO(2)) or pure oxygen breathing on renal oxygenation measured by blood oxygenation level dependent (BOLD) magnetic resonance imaging at 3.0 T. Seven healthy young volunteers (median age 25, range 23-35 years) participated in the study. A T2*-weighted fat-saturated spoiled gradient-echo sequence was implemented on a 3.0 T whole-body imager (TE/TR = 27.9 ms/49 ms, excitation angle 20 degrees ) with an acquisition time of approximately 5.3 s. A total of 100 images were acquired during 22 min. A block design was applied for gas administration: 4 min room air, 4 min carbogen/oxygen, 4 min room air, 4 min carbogen/oxygen and 6 min room air. A compartment model was fitted to the data sets accounting for time-dependent increase/decrease of renal oxygenation as well as baseline changes of the scanner. T2*-weighted images showed good image quality without notable artefacts or distortions. Mean relative signal increase due to carbogen breathing was 2.73% (95% confidence interval: 1.34-5.54) in the right kidney and 3.76% (1.53-9.20) in the left kidney, while oxygen breathing led to a signal enhancement of 3.20% (2.57-3.98) in the right kidney and 3.16% (1.83-5.45) in the left kidney. No statistical difference was found between carbogen and oxygen breathing or between the oxygenation of the right and the left kidney. A significant difference was found in the characteristic time constant for the signal increase with a faster saturation taking place for oxygen breathing. Renal tissue oxygenation is clearly influenced by carbogen or oxygen breathing. The changes can be assessed by T2*-weighted MRI at high field strengths. The effects are in the expected range for the BOLD effect of 3-4% at 3.0 T. The proposed technique might be interesting for the assessment of renal tissue oxygenation and its regulation in patients with kidney diseases.