 It is well known that X-ray contrast media can affect kidney function in some patients, especially when administered intra-arterially, and patients who already suffer from reduced kidney function and diabetes mellitus may be at increased risk. It is widely accepted to use low-osmolar or iso-osmolar contrast media, especially in patients at risk for contrast media-induced nephropathy. However, little is known about the intravenous use of X-ray contrast media in risk patients, such as contrast-enhanced CT examinations. 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. Due to the iso-osmolar feature, it is expected less influence on renal function following administration of iodixanol. 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. 