Iv contrast +/- oral. After taking the contrast, taking the images does not take long. The IV contrast has potential 2 problems. You may be allergic to it like any medicine and it may slow down the kidneys if they are not working near full capacity. Your doc can tell the risk based on blood tests of kidney function.
IV dye, CT scan. A ct scan will be performed after injection of iodinated contrast via a vein, generally in the arm. The contrast makes blood vessels more opaque to xrays, and is cleared from the blood by the kidneys. Sometimes 2 scans are done, one early (seconds to 1 minute after the injection) to look at blood flow, and a second (approx 5 min) to look at urine production and the urinary collecting system.