Radiology: Triple-bolus CT effective for kidney, urinary tract visualization

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Triple-bolus multidetector CT urography is a dose-efficient protocol that can acquire corticomedullary-nephrographic-excretory and vascular enhancement phases in a single acquisition and can provide sufficient opacification and distention of the upper urinary tract (UUT), based on the results of a study published in the May edition of Radiology. At the same time, adequate image quality of renal parenchyma and vascular anatomy is achieved by way of this method.

Maka Kekelidze, MD, PhD, and colleagues from the departments of radiology, biostatistics and urology at Erasmus Medical Center in Rotterdam, Netherlands, sought to retrospectively evaluate renal, vascular and urinary tract visualization following a single postcontrast multidetector CT urographic sequence performed with three limited-volume bolus injections.

“Many CT urographic methods use relatively high radiation doses that have been measured to be 1.5–2 times the dose of standard intravenous urography,” noted the authors. “In addition, an increased numbers of images are acquired and must be reviewed by radiologists.”

Between February 2005 and March 2006, 110 patients--consisting of 69 men with an average age of 56 and 41 women with an average age of 55--underwent triple-bolus multidetector CT urography. Triple-bolus protocol consisted of 30 mL of contrast material at 2 mL/sec at 0 seconds, 50 mL at 1.5 mL/sec at 435 seconds, 65 mL at 3 mL/sec at 488 seconds, with total abdominal scanning time of 510 seconds, the researchers explained. After the exam, UUT distention was measured by one independent reader and two independent readers rated urinary tract opacification and qualitatively- and quantitatively-assessed renal parenchymal and vascular contrast enhancement.

The authors found that complete opacification of the intrarenal collecting system and proximal ureter was achieved in 91 percent and 82 percent of analyzed segments, respectively. The distal ureter and bladder was not opacified in 21 percent, or in 20 percent of the cases, respectively.

In addition, Kekelidze and colleagues said that image quality of renal parenchymal enhancement was excellent in 76 percent of cases and arteries showed better contrast enhancement than did veins (89 vs. 59 percent of the cases). Also, radiation dose calculated for triple-bolus acquisition was 9.8 mSv.

Noting that their goal was to limit the radiation dose of unenhanced scanning as much as possible, “Our entire examination,” wrote the authors, “including unenhanced and triple-bolus scanning, exposed the patient to 13.2 mSv. This is 44 percent less than the radiation dose from our previous three-phase protocol (23.4 mSv) and is about half the effective radiation dose recently reported for three-phase multidetector CT urographic protocols.”