Early effects of an x-ray contrast medium on renal T2*/T2 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 T₂* and T₂ mapping. We studied CM effects on renal T₂*/T₂ 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. T₂*/T₂ 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 T₂*/T₂ mapping. For T₂*/T₂ 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 T₂* in C (by 17%) and all medullary layers (25-35%). Hypoxia decreased T₂* in C (40%) and all medullary layers (55-60%). AO decreased T₂* in C (18%) and all medullary layers (30-40%). Upon injection of CM, T₂* increased transiently, then decreased, reaching values 10-20% below baseline in C and OM and 30-40% below baseline in IM and P. Conclusion T₂* mapping corroborates data previously obtained with invasive methods and demonstrates that CM injection affects renal medullary oxygenation. CM-induced T₂* decrease in OM was small vs. hypoxia and aortic occlusion. T₂* decrease obtained for hypoxia was more pronounced than for AO. This indicates that T₂* may not accurately reflect blood oxygenation under certain conditions. [ABSTRACT FROM AUTHOR]