<qa>  What is the main purpose of this study?The main purpose of this study is to evaluate and compare the effects on kidney function of two contrast media, the iso-osmolar iodixanol and the low-osmolar iopamidol in patients at risk of kidney damage associated with the injection of contrast media. A standard hydration procedure, based on available guidelines will be given to all patients to prevent negative effects on the kidneys. Serum creatinine SCr concentrations will be measured before and up to 7 days after contrast media administration to evaluate the effects on renal function. 