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Ultrasound uses sound waves to provide images of the liver, gallbladder, and bile ducts. Transabdominal ultrasound is better for detecting structural abnormalities, such as tumors, than for diffuse abnormalities, such as cirrhosis (severe scarring of the liver) or fatty liver (excess fat in the liver). It is the least expensive and safest technique for creating images of the gallbladder and bile ducts.
Using ultrasound, a doctor can readily detect gallstones in the gallbladder. Ultrasound of the abdomen can distinguish whether jaundice (a yellowish discoloration of the skin and the whites of the eyes) is caused by bile duct obstruction or by liver cell malfunction. If ultrasound shows ducts that are dilated (widened), the cause is obstruction. Ultrasound also provides guidance when inserting a needle to obtain a tissue sample for biopsy. A type of ultrasound, called Doppler ultrasound, can show blood flow in the blood vessels of the liver. Doppler ultrasound can detect blockages in the liver's arteries and veins, particularly the portal vein, which brings blood from the intestine to the liver. Doppler ultrasound can also detect the effects of high blood pressure in the portal vein (portal hypertension). Endoscopic ultrasound uses a tiny probe on the top of an endoscope that is passed through the mouth into the stomach and the first segment of the small intestine (duodenum), bringing the probe closer to the liver and its surrounding organs.
Radionuclide
(radioisotope) imaging uses a substance containing a radioactive tracer that, when injected intravenously into the body, collects in a particular organ. The radioactivity is detected by a gamma-ray camera, which is positioned over the upper abdomen and is attached to a computer that generates an image. A liver scan uses a radioactive substance that collects in liver cells. Cholescintigraphy (hepatobiliary scintigraphy or scan), another type of radionuclide imaging, follows the movement of a radioactive substance as it is secreted from the liver and passes into the gallbladder and through the bile ducts into the duodenum. This technique can detect a blocked cystic duct (which joins the gallbladder to the major bile duct). Such a blockage indicates acute inflammation of the gallbladder (cholecystitis) (see Tumors of the Liver: Hepatic Granulomas).
Computed
tomography (CT) provides excellent images of the liver. It is particularly useful for detecting tumors. It can also detect collections of pus (abscesses) and some diffuse disorders, such as a fatty liver (excess fat in the liver).
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Understanding Endoscopic Retrograde Cholangiopancreatography
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In endoscopic retrograde cholangiopancreatography (ERCP), a radiopaque dye is introduced through an endoscope (a flexible viewing tube), which is inserted into the mouth and through the stomach into the duodenum (the first segment of the small intestine). The radiopaque dye is injected into the biliary tract just past the sphincter of Oddi. The dye then flows back up the biliary tract and often shows the pancreatic ducts. Surgical instruments can also be used with the endoscope, allowing a doctor to remove a stone in a bile duct or insert a tube (stent) to bypass a bile duct blocked by scarring or cancer.
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Magnetic
resonance imaging (MRI) can detect diffuse liver disorders, such as hepatitis, hemochromatosis, and Wilson's disease, which affect all areas of the liver about equally. MRI shows blood flow, providing information about blood vessel disorders. MRI technology can also provide images of the bile ducts and nearby structures, using a technique called magnetic
resonance cholangiopancreatography (MRCP). The images produced are as good as those produced by more invasive tests, in which dye is directly injected into the biliary and pancreatic ducts. Unlike CT, MRI tests do not involve exposure to x-rays, though they are more expensive than CT and take longer to perform.
Endoscopic
retrograde cholangiopancreatography (ERCP) involves passing an endoscope (a flexible viewing tube) through the mouth, esophagus, and stomach into the duodenum. A thin tube is then inserted through the endoscope into the biliary tract. A radiopaque dye is injected through the tube into the biliary tract, and x-rays are taken of the biliary tract and pancreatic duct. ERCP is occasionally used simply to see the biliary tract structures, although MRCP is usually preferred when available because it is just as good and is safer. However, unlike other diagnostic tests, biopsies and certain treatments can be done during ERCP. For example, a stone in a bile duct can be removed, or a tube (stent) can be inserted to bypass a bile duct blockage caused by cancer. With ERCP, complications (such as inflammation of the pancreas [pancreatitis] or bleeding) occur about 1% of the time. If a treatment is performed during ERCP, such complications can occur more often.
Percutaneous
transhepatic cholangiography involves inserting a long needle through the skin into the liver and then injecting a radiopaque dye into a bile duct in the liver, using ultrasound for guidance. The x-rays clearly reveal the biliary tract, particularly any blockage within the bile ducts. Like ERCP, percutaneous transhepatic cholangiography is used more often for treatment or biopsy than to obtain images of the biliary tract. Complications of percutaneous transhepatic cholangiography, such as bleeding and internal damage, make it a less desirable method than ERCP, except in special circumstances.
Operative cholangiography involves the injection of a radiopaque dye directly into the ducts of the biliary tract during gallbladder surgery. X-rays then reveal clear images of the biliary tract. This test is used only occasionally, when other, less invasive tests do not provide enough information. Operative cholangiography is more difficult when the gallbladder surgery is being performed via laparoscopy (using a flexible viewing tube and surgical instruments inserted through tiny abdominal incisions).
Simple x-rays of the abdomen usually cannot detect disorders of the liver, gallbladder, or biliary tract.
Last full review/revision October 2006 by Eldon A. Shaffer, MD
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