Evaluation of renal oxygenation change under the influence of carbogen breathing using a dynamic<i>R</i>₂,<i>R</i>₂′ and<i>R</i>₂* quantification approach

The purpose of this study is to demonstrate the feasibility of dynamic renal R2 /R2 '/R2 * measurements based on a method, denoted psMASE-ME, in which a periodic 180° 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% O2 , 3% CO2 ) breathing was employed in nine rabbits. Parametrical R2 /R2 '/R2 * maps were computed and average R2 /R2 '/R2 * 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 R2 , R2 ' and R2 * decreased significantly from 16.2 ± 4.4 s-1 , 9.8 ± 5.2 s-1 and 25.9 ± 5.0 s-1 to 14.9 ± 4.4 s-1 (p < 0.05), 8.5 ± 4.1 s-1 (p < 0.05) and 23.4 ± 4.8 s-1 (p < 0.05) in the cortex when switching the gas mixture from room air to carbogen. In the renal medulla, R2 , R2 ' and R2 * also decreased significantly from 12.9 ± 4.7 s-1 , 15.1 ± 5.8 s-1 and 27.9 ± 5.3 s-1 to 11.8 ± 4.5 s-1 (p < 0.05), 14.2 ± 4.2 s-1 (p < 0.05) and 25.8 ± 5.1 s-1 (p < 0.05). No statistically significant differences in relative R2 , R2 ' and R2 * changes were observed between the cortex and medulla (p = 0.72 for R2 , p = 0.39 for R2 ' and p = 0.61 for R2 *). The psMASE-ME method for dynamic renal R2 /R2 '/R2 * measurements, together with the respiratory challenge, has potential use in the evaluation of renal oxygenation in many renal diseases.