Pseudolesion of the bile duct caused by flow effect: A diagnostic pitfall of MR cholangiopancreatography

OBJECTIVE. Our objective was to examine the influence of the shape of imaged structures and the velocity of flow on the appearance of flow artifacts seen on MR cholangiopancreatography (MRCP) in a phantom model. MATERIALS AND METHODS. Three types of phantoms representing the biliary system were constructed. The first phantom type was a straight tube; the second, a single tube in which the inlet and outlet diameters varied by a ratio of as much as 1:6; and the third, a tube that simulated a stricture in the biliary system and a gallstone. All experiments were repeated three times. RESULTS. We did not observe any flow artifacts in the experiments we performed with the straight tubes. A higher rate of flow resulted in decreased signal intensity in tubes simulating bile ducts; the decreased signal was most likely to be observed on images in which the speed of flow exceeded 5 mm/sec. Flow artifacts were seen only if the ratio between the inlet and outlet diameters was 1:4 or greater. Simulations of bile duct abnormalities - such as a 50% stricture or the presence of a gallstone - did not produce any flow artifacts. CONCLUSION. In our experiments, a flow artifact could be seen on images in which the ratio between the inlet and the outlet diameters in the phantom was equal to or greater than 1:4. This finding indicates that a flow artifact could be observed in dilated bile ducts on MRCP under clinical conditions. Knowing that a pseudo-filling defect can be caused by a flow artifact should help to prevent misinterpretation of MRCP images.