Early effects of an x‐ray contrast medium on renal T 2 */T 2 MRI as compared to short‐term hyperoxia, hypoxia and aortic occlusion in rats

Aim X‐ray contrast media ( CM ) can cause acute kidney injury ( AKI ). Medullary hypoxia is pivotal in CM ‐induced AKI , as indicated by invasively and pin‐point measured tissue oxygenation. MRI provides spatially resolved blood oxygenation level–dependent data using T 2 * and T 2 mapping. We studied CM effects on renal T 2 */T 2 and benchmarked them against short periods of hyperoxia, hypoxia and aortic occlusion ( AO ). Methods Rats were equipped with carotid artery catheters (tip towards aorta) and supra‐renal aortic occluders. T 2 */T 2 mapping was performed using a 9.4‐T animal scanner. CM (1.5 mL iodixanol) was injected into the thoracic aorta with the animal in the scanner followed by 2 h of T 2 */T 2 mapping. For T 2 */T 2 assessment, regions of interest in the cortex ( C ), outer medulla ( OM ), inner medulla ( IM ) and papilla ( P ) were determined according to morphological features. Results Hyperoxia increased T 2 * in C (by 17%) and all medullary layers (25–35%). Hypoxia decreased T 2 * in C (40%) and all medullary layers (55–60%). AO decreased T 2 * in C (18%) and all medullary layers (30–40%). Upon injection of CM , T 2 * increased transiently, then decreased, reaching values 10–20% below baseline in C and OM and 30–40% below baseline in IM and P. Conclusion T 2 * mapping corroborates data previously obtained with invasive methods and demonstrates that CM injection affects renal medullary oxygenation. CM ‐induced T 2 * decrease in OM was small vs. hypoxia and aortic occlusion. T 2 * decrease obtained for hypoxia was more pronounced than for AO . This indicates that T 2 * may not accurately reflect blood oxygenation under certain conditions.