To Compare Intravenous and Oral Hydration of the Prevention for CIN in Elderly Patients Undergoing Intravenous CECT

Inclusion Criteria: * Age\>21 * informed consent * Undergoing Intravenous Contrast-enhanced Computed Tomography Exclusion Criteria: * CT enhancement was not performed; * Dialysis treatment of patients with end-stage renal failure or heart, kidney transplantation; * Exposure to radioactive contrast medium within 48 hours prior to or within 72 hours of examination; * Acute decompensated heart failure; * Allergic to radioactive contrast agent; * Be subjected to life - threatening trauma; * Severe infection; * Surgery was performed within 2 days of CT examination. * Combined with multiple myeloma, urinary obstruction, aortic dissection * Can cause acute kidney injury disease; * Use of aminoglycosides and other nephrotoxic drugs 2 weeks before.