Split-bolus CT urography technique cuts radiation dose

Vendors have employed a multitude of approaches to cut patient radiation dose by making data acquisition and analysis more efficient. Software has been developed to adjust dose to fit different body types and segments. Methods to factor in body weight, particularly when scanning children, have been considered. Step-and-shoot protocols have been devised to eliminate the overlap that comes from spiral scanning.

A new technique to decrease radiation dose can be added to the list.

Radiologists from Stanford University School of Medicine and the VA Palo Alto Health Care System have come up with a way to split the bolus when doing multislice CT urography, an approach that reduces both the radiation dose and number of images produced.

The technique runs counter to the trend that has surfaced since CT urography was introduced more than a decade ago. During this time, protocols have proliferated. The vast majority have involved scanning patients before contrast and at multiple phases after the administration of IV contrast.

"We wanted to show that a similar examination could be achieved with fewer scan acquisitions by administering a split bolus of IV contrast, without sacrificing sensitivity," said Dr. Lawrence C. Chow, lead author of the study, which appeared in the August issue of the American Journal of Roentgenology.

Chow, now at the Oregon Health and Science University in Portland, conducted the study while at Stanford. He and his colleagues examined 500 patients with suspected urinary tract abnormalities. In addition to unenhanced CT scanning of the abdomen and pelvis, they conducted concurrent nephrographic and excretory phase enhancement through the administration of a split contrast bolus. Split-bolus CT urography detected all proven cases of tumors of the upper urinary tract, yielding high sensitivity and specificity.

"We believe that the use of CT urography results in a simplified diagnostic evaluation for patients with painless hematuria and can potentially replace what previously required two studies: traditional excretory urography plus CT, MR, or sonography," Dr. Chow said.

The split-bolus technique also uncovered evidence of numerous congenital and other abnormalities of the urinary tract. The researchers found 14 of 19 confirmed cases of uroepithelial neoplasms involving the bladder.

"We were impressed with the wide spectrum of abnormalities we were able to see with CT urography and with the ability of CT urography to detect even very small abnormalities such as papillary necrosis, renal tubular ectasia, and very small urothelial tumors," Chow said.