CT for the evaluation of flank pain.

Unenhanced helical CT allows rapid and accurate determination of whether a stone is present anywhere in the urinary tract. There is a learning curve for both radiologist and urologist, but a number of signs are highly predictive of stone. Helical CT scans should always be accompanied by a "scoutogram" to convey an idea of what the stone might look like. The scan requires no contrast medium and takes only 5 to 10 minutes of imaging time, making it cost effective. It behooves both urologists and radiologists to familiarize themselves with the techniques for reading these scans.