Evaluation of renal oxygenation change under the influence of carbogen breathing using a dynamic R2, R2 and R2* quantification approach

The purpose of this study is to demonstrate the feasibility of dynamic renal R-2/R-2/R-2* measurements based on a method, denoted psMASE-ME, in which a periodic 180 degrees pulse-shifting multi-echo asymmetric spin echo (psMASE) sequence, combined with a moving estimation (ME) strategy, is adopted. Following approval by the institutional animal care and use committee, a block design of respiratory challenge with interleaved air and carbogen (97% O-2, 3% CO2) breathing was employed in nine rabbits. Parametrical R-2/R-2/R-2* maps were computed and average R-2/R-2/R-2* values were measured in regions of interest in the renal medulla and cortex. Bland-Altman plots showed good agreement between the proposed method and reference standards of multi-echo spin echo and multi-echo gradient echo sequences. Renal R-2, R-2 and R-2* decreased significantly from 16.2 +/- 4.4s(-1), 9.8 +/- 5.2s(-1) and 25.9 +/- 5.0s(-1) to 14.9 +/- 4.4s(-1) (p<0.05), 8.5 +/- 4.1s(-1) (p<0.05) and 23.4 +/- 4.8s(-1) (p<0.05) in the cortex when switching the gas mixture from room air to carbogen. In the renal medulla, R-2, R-2 and R-2* also decreased significantly from 12.9 +/- 4.7s(-1), 15.1 +/- 5.8s(-1) and 27.9 +/- 5.3s(-1) to 11.8 +/- 4.5s(-1) (p<0.05), 14.2 +/- 4.2s(-1) (p<0.05) and 25.8 +/- 5.1s(-1) (p<0.05). No statistically significant differences in relative R-2, R-2 and R-2* changes were observed between the cortex and medulla (p=0.72 for R-2, p=0.39 for R-2 and p=0.61 for R-2*). The psMASE-ME method for dynamic renal R-2/R-2/R-2* measurements, together with the respiratory challenge, has potential use in the evaluation of renal oxygenation in many renal diseases