Contrast-enhanced MR imaging of experimental acute tubular necrosis

Assessment with unenhanced MRI techniques of renal morphology and hemodynamic changes during acute kidney injury and chronic kidney disease in mice

BACKGROUND/AIMS

Changes in renal oxygenation and perfusion have been identified as common pathways to the development and progression of renal disease. Recently, the sensitivity of hemodynamic response imaging (HRI) was demonstrated; this is a functional magnetic resonance imaging (MRI) method combined with transient hypercapnia and hyperoxia for the evaluation of renal perfusion and vascular reactivity. The aim of this study was to utilize HRI for the noninvasive evaluation of changes in renal hemodynamics and morphology during acute, chronic and acute-on-chronic renal failures.

METHODS

Renal-HRI maps and true fast imaging with steady-state precession (True-FISP) images were used to evaluate renal perfusion, morphology and corticomedullary differentiation (CMD). MR images were acquired on two mouse models of kidney injury: adenine-induced chronic kidney disease (CKD) and rhabdomyolysis-induced acute kidney injury (AKI). Serum urea was measured from these mice in order to determine renal function.

RESULTS

Renal-HRI maps revealed a blunted response to hypercapnia and hyperoxia with evolving kidney dysfunction in both models, reflecting hampered renal vascular reactivity and perfusion. True-FISP images showed a high sensitivity to renal morphological changes, with different patterns characterizing each model. Calculated data obtained from HRI and True-FISP during the evolution of renal failure and upon recovery, with and without protective intervention, closely correlated with the degree of renal impairment.

CONCLUSIONS

This study suggests the potential combined usage of two noninvasive MRI methods, HRI and True-FISP, for the assessment of renal dysfunction without the potential risk associated with contrast-agents administration. HRI may also serve as a research tool in experimental settings, revealing the hemodynamic changes associated with kidney dysfunction.

Magnetic resonance imaging in acute and chronic kidney diseases: present status

Magnetic resonance imaging (MRI) of normal and diseased kidneys shows great promise because of the combined value of anatomical and functional information provided, as well as of specific contrast patterns that can be observed non-invasively. Multicontrast MRI is able to show infiltrative kidney disorders. Diffusion-weighted imaging can assess alterations in renal function and can suggest obstruction or inflammation when present. Due to the low nephrotoxicity, contrast-enhanced MR studies using serial dynamic enhancement with non-specific gadolinium chelates are able to provide information on glomerular filtration. Furthermore, contrast agents such as ultrasmall particles of iron oxide, specific of inflammation, should be used in the near future to detect active from quiescent involvement, both in native kidneys and renal allografts. Early results should indicate that these compounds might differentiate acute tubular necrosis from other acute nephropathies, as well as active proliferative nephropathies from chronic ones. Ongoing studies will obviously demonstrate the value of the combination of these various MRI sequences in the diagnosis of acute renal failure and chronic kidney disease.

Newly developed techniques to study and diagnose acute renal failure

Progress in treating human acute renal failure (ARF) is dependent on developing techniques that allow for the rapid diagnosis, quantification of injury, further understanding of the pathophysiology, and the effects of therapy. Therefore, four techniques that will facilitate this progress are described and illustrated by four different investigative teams. Techniques to measure rapid changes in GFR are available for rapid diagnosis and quantification of ARF in humans. State-of-the-art magnetic resonance imaging (MRI) presently allows for enhanced resolution of regional renal blood flow and functional evaluations in patients. Furthermore, new probes and techniques for MRI that allow for identification and quantitation of inflammation, applicable to human ARF, are being developed and tested in animal models. Finally, two-photon microscopy will allow for four-dimensional cellular and subcellular studies in animal models of ARF providing rapid insights into pathophysiology and the therapeutic effects of a variety of promising agents. Further development and utilization of these techniques, especially in concert with genetic, proteomic, and molecular approaches, will allow for needed insights into the pathophysiology and therapy in human ARF.