Wesley C. Chan MD, Presenter: Nothing to Disclose

Benjamin M. Yeh MD, Abstract Co-Author: Nothing to Disclose

Bonnie N. Joe MD, PhD, Abstract Co-Author: Nothing to Disclose

Robert G Gould DSC, Abstract Co-Author: Nothing to Disclose

Kimberly S Kirkwood, Abstract Co-Author: Nothing to Disclose

Fergus Vincent Coakley MD, Abstract Co-Author: Nothing to Disclose

To determine the effect of varying kVp on gallstone detection in vitro by CT.

Eighty six gallstones were classified as "small" (mean diameter = 1 cm) using physical measurement calipers and were determined to be of cholesterol or pigment composition by infrared spectroscopy. The gallstones were scanned by CT one at a time in the saline-filled “gallbladder” compartment of an anthropomorphic phantom. For each gallstone, the phantom was scanned at 80, 100, 120, and 140 kVp with 5 mm slice thickness and CT tube current adjusted to maintain similar image noise levels (10.0 HU +/- 0.5 HU). In 85 additional instances, the “gallbladder” compartment was scanned at each kVp setting when containing only saline. The scans were then randomized and two independent readers evaluated the images on a PACS workstation to record the presence and CT attenuation of gallstones. McNemar’s Chi-squared test was used to compare the sensitivity and specificity for gallstone detection between the 4 kVp settings for each reader.

The sensitivity of readers 1 and 2 for gallstone detection was significantly higher at 140 kVp (86% and 81%; or 74 and 70 out of 86 gallstones, respectively) than at 80, 100, or 120 kVp (sensitivity 67% and lower for reader 1 and 63% and lower for reader 2, corresponding to 58 or fewer and 54 or fewer of 86 gallstones respectively, p < 0.05 for each). The specificity for gallstone detection was greater than 85% (72 or more of 85 saline-only scans) for both readers at 100, 120, and 140 kVp. For each reader, the sensitivity for gallstone detection at 140 kVp was significantly higher than at 80, 100, or 120 kVp for both cholesterol and pigment gallstones (p < 0.05 for each) and both small and large gallstones (p < 0.05 for both, each).

The in-vitro sensitivity of CT for detecting both pigment and cholesterol gallstones is significantly greater at 140 kVp than at lower kVp, likely due to greater absorption of higher energy X-rays by gallstones than by saline. In patients with upper abdominal pain undergoing first-line CT, scanning at 140 kVp may improve gallstone detection.

Chan, W, Yeh, B, Joe, B, Gould, R, Kirkwood, K, Coakley, F, Does kVp Influence the CT Detection of Gallstones in Vitro?.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4418301.html