MDCT artifact related to the intra-scan gravitational flow of opacified luminal fluid (the “Dense Waterfall” sign)

Abstract

To describe and characterize a distinctive MDCT artifact related to intra-scan transit of contrast-enhanced luminal fluid, which we term the "dense waterfall". 179 consecutive CT colonography studies were reviewed for the presence of this distinctive artifact within the prepared and distended colon. In addition, a phantom was constructed to reproduce this artifact. A luminal artifact consisting of a starburst-like cluster of bright arciform streaks was identified within the colon in 23.5% (42/179) of patients and 19.0% (68/358) of series. The artifact was not associated with patient motion, peristalsis, or spasm but was always associated with opacified fluid actively flowing from a higher to lower level relative to the table. The average luminal fluid attenuation was 764±205HU in cases where the artifact was present, which was unchanged from cases without the artifact (762±204HU) and was not sufficiently high enough to cause obvious beam-hardening artifact in static fluid. Scans of the phantom simulation reproduced this artifact, confirming its origin. Active gravitational flow of contrast-enhanced luminal fluid creates a distinctive arciform starburst artifact at MDCT that could be confused with patient motion, spasm, or beam hardening. To our knowledge, this artifact has not been previously described. Although commonly seen at CT colonography due to the specific colonic preparation and distention technique, this artifact can be seen on other abdominal MDCT studies. This artifact would generally not be confused for underlying pathology, but could potentially obscure relevant findings.