Excretory urography — a technique for evaluating the kidneys that involves injecting a contrast agent intravenously and taking x-rays — is the conventional method used to image the upper urinary tract, including the kidneys and ureters. Recently, cross-sectional imaging techniques, such as multidetector CT urography, have become more popular because they provide better images. However, the multidetector scanners used in CT urography often require three or four imaging passes per examination. This means a significant amount of radiation exposure for patients as well as a high number of images that must be interpreted for each examination.As reported in the August issue of the American Journal of Roentgenology, Dr. Lawrence C. Chow and his colleagues from Stanford University School of Medicine in California evaluated the use of a time-delayed contrast-material-enhanced CT urography technique to see whether it could effectively detect urinary tract abnormalities with fewer imaging passes.The researchers tested 500 patients with possible urinary tract abnormalities using their split-bolus CT urography method, which involved administering two time-delayed doses of IV contrast material about 4 min apart. They obtained images in synchronous nephrographic and excretory phases of enhancement 120 s after the second contrast bolus with multidetector scanners from GE Healthcare.The technique identified 100 percent of pathologically confirmed renal cell carcinomas and uroepithelial malignancies. It also confirmed 14 out of 19 cases of uro-epithelial growths involving the bladder. In addition, it allowed the researchers to eliminate one or more of the traditionally required imaging sessions by enabling imaging of the nephrographic and excretory phases in a single pass.The investigators believe that their results indicate that the split-bolus multidetector CT urography technique may be able to reduce both radiation dose and the number of images that are generated.