Noninvasive measurement of renal oxygen extraction fraction under the influence of respiratory challenge.

Abstract

To demonstrate the feasibility of using a susceptibility-based magnetic resonance imaging (MRI) technique for measuring renal oxygen extraction fraction (OEF) changes under the influence of carbogen (97% O2 , 3% CO2 ) breathing. Eight New Zealand White rabbits were included in this study with local animal care committee approval. For OEF measurement, an asymmetric spin echo (ASE) sequence was used to acquire source images and a susceptibility model was utilized for OEF estimation at 3.0T. Within-session and between-day tests were conducted to evaluate the reproducibility of this OEF measurement. OEF changes were measured under respiratory challenge with alternated air and carbogen (97% O2 , 3% CO2 ) breathing. For comparison, blood samples were collected for the measurement of pO2 . The within-session coefficients of variation (CVs) of renal OEF measurements were 6.62% in cortex and 5.92% in medulla, while between-day CVs were 7.52% in cortex and 8.03% in medulla. Under carbogen breathing, renal OEFs decreased significantly from 0.32 ± 0.03 to 0.28 ± 0.02 (P < 0.01) in cortex, and from 0.34 ± 0.04 to 0.31 ± 0.03 (P < 0.01) in medulla. No statistical difference of relative OEF change was seen between cortex and medulla (P = 0.93). In addition, negative correlation between renal OEF and blood pO2 was found (r = 0.68 (P < 0.05) in cortex, and r = 0.64 (P < 0.05) in medulla). This study demonstrates the feasibility of using a susceptibility-based OEF measurement method for the evaluation of renal oxygenation changes induced by carbogen breathing. J. Magn. Reson. Imaging 2016;44:230-237.