N-acetylcysteine is used to reduce the risk of injury to the kidney after the administration of contrast dye. The mechanism and effectiveness of this intervention is not substantiated in the literature. The investigators hypothesize that serum creatinine will be lower in patients who receive NAC compared to those who receive the placebo but serum cystatin C will not change in patients who receive NAC compared to those who receive the placebo. Also urine creatinine will increase after the administration of NAC compared to before the administration of NAC.