Hepatic arteries and the parallel-channel sign.
The sonographic parallel-channel sign is not pathognomonic of dilatation of the biliary tree. Often, the so-called parallel channel is a hepatic artery. The differentiation between a bile duct and a hepatic artery is usually possible with good sonographic technique.
D001652:Bile Ducts / Q000033:anatomy & histology*; D001660:Biliary Tract Diseases / Q000175:diagnosis; D004108:Dilatation, Pathologic / Q000175:diagnosis; D006499:Hepatic Artery / Q000033:anatomy & histology*; D006801:Humans; D011169:Portal Vein / Q000033:anatomy & histology; D014463:Ultrasonography