Liver 3

Gastrointestinal System Nuclear Medicine Par t 3 Hepatobiliary Imaging

Physiology ◆

Hepatic cells secrete about 1 liter of bile per day. Bilirubin is the final degradation product of porphyrin metabolism, and its principal source is the catabolism of hemoglobin. Bilirubin is extracted from the plasma by the hepatocyte, conjugated with glucuronic acid, and excreted into the bile canuliculi.

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Conjugated hyperbilirubinemia usually indicates the presence of biliary obstruction. Common bile duct flow is solely passive, but the cystic duct may function as a variable resistor that actively regulates flow into and out of the gallbladder.

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The biliary canals permit the passage of bile from the liver to the duodenum.The right and left hepatic ducts join at the porta hepatis to form the common hepatic duct,which in turn combines with the cystic duct to form the common bile duct .This is 10-15cm long, and is joined at its distal end by the main pancreatic duct;

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They enter the wall of the duodenum at the ampulla of Vater.. The gall- bladder is attached to the inferior surface of the liver. It is usually about 10cm in length and 3-5cm in diameter .It serves as a reservoir of bile and renders it more concentrated .It connects with bile biliary tree through the cystic duct.

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Principle The hepatic parenchymal (polygonal) cells constitute 85% of the hepatic mass. Their function can be studied by radiotracers such as Tc-99m labelled iminodiacetic acid (IDA) or its derivatives which are selectively extracted by the liver polygonal cells and excreted into the bile.

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Biliary imaging has become the procedure of choice in evaluating patients with suspected acute cholecystitis because in virtually all cases of acute cholecystitis there is obstruction of the cystic duct with no passage of radionuclide into the gallbladder.

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The test can also be used to detect enterogastric reflux of bile and neonatal biliary atresia as well as to assess biliary kinetics (gallbladder ejection fraction) in suspected chronic cholecystitis.

Indications: 1. Diagnosis of acute cholecystitis and differentiate between acute cholecytitis and pancreatitis ◆ 2. Diagnosis of biliary atresia, ◆ 3.Demonstration of patency of cystic and common bile duct whenever oral or intravenous cholecystograms are not applicable. ◆

4. Demonstration of improvement of bile flow after relieve of obstruction, ◆ 5. Demonstration of complete obstructive jaundice. ◆ 6.Work-up of patients with biliary dyskinesis. ◆ 7. Study of bile reflux, postoperative gastroduodenal reflux. ◆

Radiopharmaceuticals ◆ A variety of radiopharmaceuticals have been synthetized with the specific aim of imaging the biliary system.An important advance was achieved in the early 1970s with the introduction of compounds which reach high concentration in bile and are produced by standard 99mTc-lablling techniques of the 99mTe -lablled compounds,

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iminodiacetic acid derivatives are the most promising and also the most widely used. They fulfil basic requirements for hepatobiiary radiopharmaceuticals, their molecular weight varies from 300 to 1000.

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and all compounds are organic anions,bind to serum albumin,and usually contain two ring structures in opposite planes in the molecule.They are responsible for chelation with 99mTe on the one end and biliary excretion properties on the other end of the molecule.

The commonly 99mTe-iminodiacetic(IDA) derivatives used for hepatohiliary imaging are: ◆ 99mTe -HIDA, 99mTe -EHIDA, 99mTe -DISIDA . They are transported to the liver bound to albumin and are actively taken up by the hepatocytes following the same anionic pathway as bilirubin. ◆

HIDA: 85% excreted by the liver, 15% by the kidneys ◆ Good visualization at bilirubin levels of 5-7 mg/dl ◆

Patient Preparation The patient should fast for 4 hours before the study commences but not more than 12 hours ◆ The patient should fast and not eat within 4 hours of the study as the ingestion of food may result in gallbladder contraction and consequently a false positive diagnosis ; ◆

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the patient has fasted for more than 12 hours or has not eaten in many days then HIDA may have delayed filling of gallbladder because it is filled with bile.

Acquisition Parameters. ◆

Imaging can be performed in either of 2 ways:

◆ 1.Sequential statics: After injection the patient then take 3 minute anterior images at 5 min,l5min,20 min,30 min,40 min,50 min. and 60 min intervals. If the gallbladder has delayed filling then arrange for the patient to have a meal and reimage 3 hours later and see if the gallbladder has filled.

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Continuous acquisition:

If you use the continuous acquisition method then the patient is positioned under the gamma camera and the computer acquisition is set up to erect for a dynamic phase (frames/min for 60mins).The patient is asked to lay down in the supine position.

Normal Imaging ◆

After intravenous administration of 99mTe -HIDA: There is rapid uptake of the tracer by the liver. Then 99mTc-HIDA passes from the liver towards the porta hepatis and hepatic ducts. The common bile duct and cystic duct become visible and the gallbladder normally fills ( or seen) within 30 minutes after injection.

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At this time the loops of the duodenum are seen. Clearance of the activity from the liver starts within 10-15 minutes and is only just visible at the end of the study.

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that means that the tracer pass out of the liver. ◆ The gallbladder is still visible at 60 minutes post injection and it should be cleared from the liver.

Clinical Usage

1.Acute cholecystitis ◆

Cholelithiasis is the formation of stones in the biliary tree and is a relatively common disease . If the stone become s wedged in the cystic duct , this can cause acute cholecystitis.

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A confident diagnosis of acute cholecystitis can be made with a clinical picture of acute upper abdominal pain associated with fever, an acutely tender and usually palpable gall bladder, and transient jaundice.

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In more difficult cases investigation is required, and 99mTc-labelled hepatobiliary pharmaceuticals have been shown to have a place in the diagnosis, and the test is a very easy , harmless , high sensitivity and high specificity method.

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silent gallbladder, especially persistent non visualization at 4 hours post injection is virtually diagnosis of acute cholecystitis.

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The reason is that the gallbladder is unable to concentrate activity when the cystic duct is inflamed and obstructed . the sensitivity of 99mTc- IDE cholescintigraphy in making this determination exceeds 95%, and the specificity approaches 99 %, leading to an overall accuracy of > 97% in the acute situation..

2. Chronic cholecystitis ◆

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Delayed visualization between 1-4 hours in a patient with normal liver function is a reliable sign of chronic cholecystitis Although delayed visualization of the gallbladder beyond 1 hour postinjection occurs most commonly in patients with chronic cholecystitis, the role of 99mTc-IDA imaging in diagnosing chronic cholecystistis is limited for many reasons.

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The majority of patients with chronic cholecystitis exhibit normal visualization of the gallbladder (85-90%). Delayed visualization of the gallbladder ( Between 1 to 4 hours of the exam) is considered fairly characteristic for chronic cholecystitis when seen, but delayed visualization can also be seen in a very small number of patients with acute cholecystitis (3.5%).

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The longer the delay in visualization , the higher the correlation with chronic cholecystitis. Visualization of bowel activity prior to visualization of the gallbladder is a nonsensitive, but rather specific finding in patients with chronic cholecystitis (In most normals, the gallbladder is seen before bowel activity). This sign indicates chronic cholecystitis about 75% of the time.

3. Jaundice ◆

In jaundiced patients it is important to distinguish between intrahepatic (nonobstructive) and extrahepatic(obstructive) cholestasis which are treated medically and surgically respectively. In specific instances, biliary scintigraphy may be useful in cases of acute common bile duct obstruction when functional stasis is detectable before dilation, and occasionally even before liver function tests become abnormal.

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Extrahepatic bile duct obstruction causes an increase in the ductal hydrostatic pressure until the point where further hepatocyte excretion is no longer possible. In acute common bile duct obstruction (0 to 24 hours) there is generally prompt hepatic uptake of the tracer without visualization of the biliary tree and no gastrointestinal activity (unless obstruction is partial).

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Hepatic function remains normal during this early period. Between 24 and 96 hours, there is a mild to moderate decrease in hepatic function. Beyond 96 hours, there is very poor hepatic uptake and the scintigraphic findings are difficult to distinguish from hepatitis.

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If the bile ducts are visualized, tracer activity within a normal common duct should be less on a 2 hour image, than on a 1.5 hour image. If ductal activity is unchanged or more intense on later images, some degree of obstruction is likely present. Intrahepatic cholestasis can produce a pattern identical to complete CBD obstruction.

4. Biliary Atresia: In biliary atresia there is usually normal prompt clearence of tracer from the blood and normal hepatic concentration with a high liver to heart ratio at 5 minutes. Subsequently, there is NO EXCRETION from the liver (nonvisualization of the biliary tree and bowel).

5. Neonatal hepatitis ◆

Depending on the severity of cholestasis and hepatocellular dysfunction, different scan patterns may be noted. Typically, patients with neonatal hepatitis will demonstrate poor hepatic uptake (due to hepatocellular dysfunction) of the tracer with poor biliary excretion, delayed transit into the bowel, and renal excretion..

6. Biliary leakage ◆

99mTc- IDA provides a sensitive means of identifying, localizing, and permitting serial evaluation of biliary leaks. After surgery, the preferential route of bile flow can be traced ,

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whether through a surgical anastomosis or into a abnorma1 collection,without introduction of nonphysiologic artifacts from pressure injection through catheters or risk of infection and other complications.

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The scintigraphic finding diagnostic for a bile leak is extravasation of tracer activity into the peritoneal cavity. Up to 50% of bile leaks can be missed, however, if delayed images (at 4 hours) are not performed. Delayed images are helpful because the bile leak activity will frequently intensify over time. Most bile leaks will be detected in 4 to 6 hours, but rarely a leak may not be identified until 24 hours after injection. Therefore, 24 hour delayed images should be obtained

7. Choledochal cysts ◆

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The typical cholescintigraphic appearance is a photon-deficient mass in the region of the porta hepatis and it can fills on delayed images (2- 4 hours post injection).

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Cho1edocha1 cysts are caused by irregular development of the sphincter of oddi and the junction of the pancreatic and common bile ducts, which permit the reflux of pancreatic juice into the common bile duct to result in inflammation, fibrosis, obstruction and consequent dilation.

Normal Imaging

Acute cholecystitis

Acute cholecystitis

Chronic cholecystitis

Intrahepatic Obstuction

Extrahepatic Obstuction

Cholestasis

Neonatal Hepatitis Syndrome

Cystic Duct Obstruction

Cystic Duct Cyst

Sketch Map

Bile Leak

Class is over , let’s go home!!!