Study: Low-dose CT scan effective in detecting ureteral calculi

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The comparison of conventional CT protocols to ultra low-dose CT in the detection of distal ureteral calculi in cadaveric models yielded similar results, according to a study published in the January issue of the Journal of Urology, suggesting that low-dose CT can be utilized as a method of diagnosis for this condition.

The calculus in the ureter is usually the result of the passage of one originating in the kidney, and is more common in males than females.

In terms of imaging modalities, unenhanced multidetector CT is currently the typical choice of physicians for detecting urinary calculi, said lead author Chris Pak, MD, professor of internal medicine at the University of Texas Southwestern Medical Center in Dallas, and colleagues.

However, the researchers said that by using low-dose CT in place of unenhanced multidetector CT, radiation dose received by a patient can be decreased by 95 percent and the risk of secondary malignancies may be reduced as a result.

For the study, Pak and colleagues utilized 85 calcium oxalate stones, ranging in size from 3 to 7 mm long.  In 56 random configurations, the stones were prospectively placed in 14 human cadaveric distal ureters. The intact kidneys, ureters and bladders were then placed in a human cadaveric vehicle and CT scanning was performed at 140, 100, 60, 30, 15 and 7.5 mA seconds while keeping other imaging parameters consistent.

Two blinded radiologists independently reviewed the images in random order to determine the sensitivity and specificity of both the conventional and the low-dose setting, and found that ureteral calculi were detected in a very similar fashion, said the researchers.

Low-dose imaging was found to have an overall sensitivity rate of 98 percent, and an 83 percent rate of specificity. The authors also reported 98, 97, 97, 96, 98 and 97 percent sensitivity ratings for images that used 140, 100, 60, 30, 15 and 7.5 mA second settings, and specificity rates of 83, 83, 83, 86, 80 and 84 percent for each setting, respectively.

The authors wrote that any false-negative results were noted for 3 mm calculi at a similar frequency at each mA second setting.  “There was no significant difference in sensitivity or specificity at any mA second settings,” concluded Pak and colleagues.