Liver, biliary tract and pancreas

Methods of imaging the hepatobiliary system

1.
Plain film
2.
Ultrasound (US):
- (a)
  Transabdominal
- (b)
  Endoscopic
- (c)
  Intraoperative
3.
CT including:
- (a)
  Routine ‘staging’ (portal venous phase) CT
- (b)
  Triple phase ‘characterization’ CT
- (c)
  CT cholangiography
4.
MRI
5.
Endoscopic retrograde cholangiopancreatography (ERCP)
6.
Percutaneous transhepatic cholangiography (PTC)
7.
Operative cholangiography
8.
Postoperative (T-tube) cholangiography
9.
Angiography – diagnostic and interventional
10.
Radionuclide imaging:
- (a)
  Static, with colloid
- (b)
  Dynamic, with iminodiacetic acid derivatives.

Methods of imaging the pancreas

1.
Plain abdominal films
2.
US:
- (a)
  Transabdominal
- (b)
  Intraoperative
- (c)
  Endoscopic.
3.
CT
4.
MRI
5.
ERCP
6.
Arteriography:
- (a)
  Coeliac axis
- (b)
  Superior mesenteric artery.

Plain films

May be useful to demonstrate air within the biliary tree or portal venous system, opaque calculi or pancreatic calcification.

Ultrasound of the liver

Indications

1.
Suspected focal or diffuse liver lesion
2.
Jaundice
3.
Abnormal liver function tests
4.
Right upper-quadrant pain or mass
5.
Hepatomegaly
6.
Suspected portal hypertension
7.
Staging known extrahepatic malignancy
8.
Pyrexia of unknown origin
9.
To facilitate the placement of needles for biopsy, etc.
10.
Assessment of portal vein, hepatic artery or hepatic veins
11.
Assessment of patients with surgical shunts or transjugular intrahepatic portosystemic shunt (TIPS) procedures
12.
Follow-up after surgical resection or liver transplant.

Contraindications

None.

Patient preparation

Not imperative, but fasting or restriction to clear fluids only required if the gallbladder is also to be studied.

Equipment

3–5-MHz transducer and contact gel. Selection of the appropriate pre-set protocol and positioning of focal zone will depend upon the type of machine, manufacturer and patient habitus.

Technique

1.
Patient supine
2.
Time-gain compensation set to give uniform reflectivity throughout the right lobe of the liver
3.
Suspended inspiration
4.
Longitudinal scans from epigastrium or left subcostal region across to right subcostal region. The transducer should be angled up to include the whole of the left and right lobes
5.
Transverse scans, subcostally, to visualize the whole liver
6.
If visualization is incomplete, due to a small or high liver, then right intercostal, longitudinal, transverse and oblique scans may be useful. Suspended respiration without deep inspiration may allow useful intercostal scanning. In patients who are unable to hold their breath, real-time scanning during quiet respiration is often adequate. Upright or left lateral decubitus positions are alternatives if visualization is still incomplete
7.
Contrast-enhanced ultrasound of the liver uses microbubble agents to enable the contrast enhancement pattern of focal liver lesions, analogous to contrast-enhanced CT or MRI, to be assessed and thus to characterize them. It requires specific software on the ultrasound machine. The lesion to be interrogated is identified on conventional B mode scanning and then the scanner is switched to low mechanical index (to avoid bursting the bubbles too quickly) contrast-specific scanning mode with a split screen to allow the contrast-enhanced image to be simultaneously viewed with the B mode image. The images are recorded after bolus injection of the contrast agent flushed with saline.

Additional views

Hepatic veins

These are best seen using a transverse intercostal or epigastric approach. During inspiration, in real time, these can be seen traversing the liver to enter the inferior vena cava (IVC). Hepatic vein walls do not have increased reflectivity in comparison to normal liver parenchyma. The normal hepatic vein waveform on Doppler is tri-phasic reflecting right atrial pressures. Power Doppler may be useful to examine flow within the hepatic segment of the IVC since it is angle-independent.

Portal vein

The longitudinal view of the portal vein is shown by an oblique subcostal or intercostal approach. Portal vein walls are of increased reflectivity in comparison to parenchyma. The normal portal vein blood flow is towards the liver. There is usually continuous flow but the velocity may vary with respiration.

Hepatic artery

This may be traced from the coeliac axis, which is recognized by the ‘seagull’ appearance of the origins of the common hepatic artery and splenic artery. There is normally forward flow throughout systole and diastole with a sharp systolic peak.

Common bile duct

See below in ‘ Ultrasound of the gallbladder and biliary system ’.

Spleen

The spleen size should be measured in all cases of suspected liver disease or portal hypertension. Ninety-five percent of normal adult spleens measure 12 cm or less in length, and less than 7 × 5 cm in thickness. The spleen size is commonly assessed by ‘eyeballing’ and measurement of the longest diameter. In children, splenomegaly should be suspected if the spleen is more than 1.25 times the length of the adjacent kidney, normal ranges have also been tabulated according to age and sex.

References

1. Loftus WK, Metreweli C: Ultrasound assessment of mild splenomegaly: spleen/kidney ratio. Pediatr Radiol 1998; 28: pp. 98-100.
2. Megremis SD, Vlachonikolis IG, Tsilimigaki AM: Spleen length in childhood with US: normal values based on age, sex, and somatometric parameters. Radiology 2004; 231: pp. 129-134.

Ultrasound of the gallbladder and biliary system

Indications

1.
Suspected gallstones
2.
Right upper quadrant pain
3.
Jaundice
4.
Fever of unknown origin
5.
Acute pancreatitis
6.
To assess gallbladder function
7.
Guided percutaneous procedures.

Contraindications

None.

Patient preparation

Fasting for at least 6 h, preferably overnight. Water may be permitted.

Equipment

3–5-MHz transducer and contact gel. Selection of the appropriate pre-set protocol and positioning of focal zone will depend upon the type of machine, manufacturer and patient habitus. A stand-off may be used for a very anterior gallbladder.

Technique

1.
The patient is supine.
2.
The gallbladder can be located by following the reflective main lobar fissure from the right portal vein to the gallbladder fossa
3.
Developmental anomalies are rare but the gallbladder may be intrahepatic or on a long mesentery. In the absence of a previous cholecystectomy the commonest cause for a non-visualized gallbladder is when a gallbladder packed with stones is mistaken for a gas-filled bowel (usually duodenal) loop.
4.
The gallbladder is scanned slowly along its long axis and transversely from the fundus to the neck leading to the cystic duct.
5.
The gallbladder should then be re-scanned in the left lateral decubitus or erect positions because stones may be missed if only supine scanning is performed.
6.
Visualization of the neck and cystic ducts may be improved by head-down tilt.

The normal gallbladder wall is never more than 3-mm thick.

Additional views

Assessment of gallbladder function

1.
Fasting gallbladder volume may be assessed by measuring longitudinal, transverse and antero-posterior (AP) diameters.
2.
Normal gallbladder contraction reduces the volume by more than 25%, 30 min after a standard fatty meal. Somatostatin, calcitonin, indometacin and nifedipine antagonize this contraction.

Intrahepatic bile ducts

1.
Left lobe: transverse epigastric scan
2.
Right lobe: subcostal or intercostal longitudinal oblique.

Normal intrahepatic ducts are visualized with modern scanners. Intrahepatic ducts are dilated if their diameter is more than 40% of the accompanying portal vein branch. There is normally acoustic enhancement posterior to dilated ducts but not portal veins. Dilated ducts have a beaded branching appearance.

Extrahepatic bile ducts

1.
The patient is supine or in a lateral position.
2.
The upper common duct is demonstrated on a longitudinal oblique, subcostal or intercostal scan running anterior to the portal vein. The right hepatic artery is often seen crossing transversely between the two.
3.
The common duct may be followed downwards along its length through the head of the pancreas to the ampulla and, when visualized, transverse scans should also be performed to improve detection of intraduct stones. However, gas in the duodenum often impedes the view of the lower duct.

The segment of bile duct proximal to the junction with the cystic duct (the common hepatic duct) is 4 mm or less in a normal adult; 5 mm is borderline and 6 mm is considered dilated. The lower bile duct (common bile duct) is normally 6 mm or less. Distinction of the common hepatic duct from the common bile duct depends on identification of the junction with the cystic duct. This is usually not possible with US. Colour-flow Doppler enables quick distinction of bile duct from ectatic hepatic artery. In less than one-fifth of patients the artery lies anterior to the bile duct.

Post-cholecystectomy

There is disagreement as to whether the normal common duct dilates after cholecystectomy. Symptomatic patients and those with abnormal liver function tests should have further investigations if the common duct measures more than 6 mm.

Ultrasound of the pancreas

Indications

1.
Suspected pancreatic tumour
2.
Pancreatitis or its complications
3.
Epigastric mass
4.
Epigastric pain
5.
Jaundice
6.
To facilitate guided biopsy and/or drainage.

Contraindications

None.

Patient preparation

Nil by mouth, preferably overnight.

Equipment

Technique

1.
The patient is supine.
2.
The body of the pancreas is located anterior to the splenic vein in a transverse epigastric scan.
3.
The transducer is angled transversely and obliquely to visualize the head and tail.
4.
The tail may be demonstrated from a left intercostal view using the spleen as an acoustic window.
5.
Longitudinal epigastric scans may be useful.
6.
The pancreatic parenchyma increases in reflectivity with age, being equal to liver reflectivity in young adults.
7.
Gastric or colonic gas may prevent complete visualization. This may be overcome by left and right oblique decubitus scans or by scanning with the patient erect. Water may be drunk to improve the window through the stomach and the scans repeated in all positions. One cup is usually sufficient. Degassed water is preferable.

The pancreatic duct should not measure more than 3 mm in the head or 2 mm in the body.

Endoscopic US (see p. 78 ) and intraoperative US are useful adjuncts to transabdominal US. EUS may be used to further characterize and biopsy pancreatic solid and cystic lesions. Intraoperative US is used to localize small lesions (e.g. islet cell tumours prior to resection).

Computed tomography of the liver and biliary tree

Indications

1.
Suspected focal or diffuse liver lesion
2.
Staging known primary or secondary malignancy
3.
Abnormal liver-function tests
4.
Right upper-quadrant pain or mass
5.
Hepatomegaly
6.
Suspected portal hypertension
7.
Characterization of liver lesion
8.
Pyrexia of unknown origin
9.
To facilitate the placement of needles for biopsy, etc.
10.
Assessment of portal vein, hepatic artery or hepatic veins
11.
Assessment of patients with surgical shunts or transjugular intrahepatic portosystemic shunt (TIPS) procedures
12.
Follow-up after surgical resection or liver transplant.

Contraindications

1.
Pregnancy
2.
Contraindication to iodinated intravenous (i.v.) contrast medium (contrast-enhanced computed tomography (CECT)) – see Chapter 2 .

Technique

Single-phase (portal phase) contrast-enhanced CT

This is the technique for the majority of routine liver CT imaging. The liver is imaged during the peak of parenchymal enhancement, i.e. when contrast-medium-laden portal venous blood is perfusing the liver. This begins about 60–70 s after the start of a bolus injection. Oral contrast may be given but is not necessary if only the liver is being investigated. Slice thickness will depend upon the CT scanner specification but should be 5 mm or less.

Multiphasic contrast-enhanced CT

The fast imaging times of helical/multislice CT enable the liver to be scanned multiple times after a single bolus injection of contrast medium. Most primary liver tumours receive their blood supply from the hepatic artery, unlike normal hepatic parenchyma, which receives 80% of its blood supply from the portal vein. Liver tumours (particularly hypervascular tumours) will therefore enhance strongly during the arterial phase (beginning 20–25 s after the start of a bolus injection) but are of similar or lower density to enhanced normal parenchyma during the portal venous phase (washout). Some tumours are most conspicuous during early-phase arterial scanning (25 s after the start of a bolus injection), others later, during the late arterial phase 35 s after the start of a bolus injection. Thus a patient who is likely to have hypervascular primary or secondary liver tumours should have an arterial phase scan as well as a portal venous phase CT scan (see above). Early and late arterial phase with portal venous phase is appropriate for patients with suspected hepatocellular cancer (triple phase). In general, late arterial and portal venous scans are appropriate to investigate suspected hypervascular metastases. Some centres, however, also use a ‘delayed’ or ‘equilibrium’ phase scan at 180 seconds to help identify and characterize primary liver tumours (quadruple phase). Terminology may be potentially confusing as some centres may consider a triple phase scan to include arterial, portal and delayed scans. Non-contrast examinations have limited usefulness.

Haemangiomas often show a characteristic peripheral nodular enhancement and progressive centripetal ‘fill-in’. After the initial dual- or triple-phase protocol, delayed images at 5 and 10 min are obtained through the lesion.

Computed tomographic cholangiography

Magnetic resonance (MR) cholangiography is non-invasive but sometimes fails to display the normal intrahepatic ducts. Multidetector CT cholangiography can be useful in this instance. With this technique the biliary tree is opacified using an i.v. cholangiographic agent. Isotropic data from 0.625 mm section thickness slices can be reconstructed to provide high-resolution three-dimensional images. Insufficient opacification may be seen with excessively dilated ducts.

Contraindications

Allergy to iodinated contrast agents.

Indications

1.
Screening for cholelithiasis
2.
Pre-operative screening of anatomy
3.
Suspected traumatic bile-duct injury
4.
Other biliary abnormalities, e.g. cholesterol polyps, adenomyomatosis and congenital abnormalities.

Technique

1.
Patient fasted for at least 6 h.
2.
100 ml i.v. cholangiographic agent, e.g. meglumine iotroxate (biliscopin R) infused for 50 min as a biliary contrast or iodipamide meglumine 52% – 20 ml diluted with 80 ml of normal saline infused over 30 min.
3.
CT scan should be obtained at least 35 min after infusion of contrast agent.

References

1. Hyodo T, Kumano S, Kushihata F, et. al.: CT and MR cholangiography: advantages and pitfalls in perioperative evaluation of biliary tree. Br J Radiol 2012; 85: pp. 887-896.
2. Schindera ST, Nelson RC, Paulson EK, et. al.: Assessment of the optimal temporal window for intravenous CT cholangiography. Eur Radiol 2007; 17: pp. 2531-2537.

Computed tomography of the pancreas

Indications

1.
Epigastric pain
2.
Obstructive jaundice
3.
Suspected pancreatic malignancy
4.
Acute pancreatitis and its complications
5.
Chronic pancreatitis and its complications.

Contraindications

1.
Pregnancy
2.
Contraindication to iodinated intravenous contrast medium – see Chapter 2 .

Technique

1.
Negative (e.g. water) oral contrast is generally preferred but positive (e.g. iodinated) may be given if necessary to opacify distal bowel loops. Positive oral contrast agent is contraindicated if CT angiography is to be performed. Volume and timing of oral contrast agent will depend upon whether opacification of distal bowel loops is required.
2.
Venous access is obtained.
3.
The patient is scanned supine and a scout view is obtained.
4.
A non-contrast-enhanced examination can be performed initially if detection of subtle calcification is required.
5.
The volume of i.v. contrast used will depend upon the type of scanner. Faster acquisition will allow a smaller volume of contrast, generally 100 ml or less. The timing of the scan in relation to i.v. contrast will depend upon the clinical question. Pancreatic phase enhancement (40 s after commencement of bolus injection) is necessary for optimum contrast differences between pancreatic adenocarcinoma and normal pancreatic tissue, with portal venous phase scans included in the protocol to investigate hepatic metastatic disease. Islet cell tumours and their metastases may show avid enhancement on arterial phase scans and become isodense with normal pancreatic tissue on portal phase scans. A portal phase scan is generally necessary to investigate flow and the relationship of the tumour to the portal vein.
6.
The volume and strength of the i.v. contrast will depend upon the speed of the scanner.
7.
Slice thickness should be 3 mm or less.

Magnetic resonance imaging of the liver

Indications

1.
Lesion characterization following detection by CT or US
2.
Lesion detection, particularly prior to hepatic resection for hepatic metastatic disease.

Magnetic resonance imaging (MRI) is rapidly emerging as the imaging modality of choice for detection and characterization of liver lesions. There is high specificity with optimal lesion-to-liver contrast and characteristic appearances on differing sequences and after contrast agents. Focal lesions may be identified on most pulse sequences. Most metastases are hypo- to isointense on T1 and iso- to hyperintense on T2-weighted images. However, multiple sequences are usually necessary for confident tissue characterization. The timing, degree and nature of tumour vascularity form the basis for liver lesion characterization based on enhancement properties. Liver metastases may be hypo- or hyper-vascular.

Magnetic resonance imaging pulse sequences

Common pulse sequences are:

1.
T1-weighted spoiled gradient echo (GRE). This has replaced the conventional spin-echo sequence. In and out of phase scans are used to investigate patients with suspected fatty liver.
2.
Magnetization-prepared T1-weighted GRE. A further breath-hold technique with very short sequential image acquisition.
3.
T1-W GRE fat-suppressed volume acquisition. This sequence can be obtained rapidly following i.v. gadolinium.
4.
T2-weighted spin echo (SE). T2-weighted fast spin-echo (FSE; General Electric) or turbo spin-echo (TSE; Siemens).

Compared with conventional T2-weighted SE images, FSE/TSE images show:

1.
Fat with higher signal intensity
2.
Reduced magnetic susceptibility effects which are of advantage in patients with embolization coils, IVC filters, etc., but disadvantageous after injection of superparamagnetic oxide contrast agent
3.
Increased magnetization transfer which may lower signal intensity for solid liver tumours. These sequences may be obtained with fat suppression.

Fat suppression:

1.
Decreases the motion artifact from subcutaneous and intra-abdominal fat
2.
Increases the dynamic range of the image
3.
Improves signal-to-noise and contrast-to-noise ratios of focal liver lesions.

Very heavily T2-weighted sequences can be used to show water content in bile ducts, cysts and some focal lesions. These may be obtained as:

1.
Gradient echo breath-hold sequences (e.g. fast imaging with steady state precession (FISP), fast imaging employing steady state acquisition (FIESTA)) or
2.
breath-hold very fast spin echo, e.g. half Fourier acquisition single-shot turbo spin echo (HASTE) or
3.
non-breath-hold respiratory gated sequences used for magnetic resonance cholangiopancreatography (MRCP).

Fat suppression is also used to allow better delineation of fluid-containing structures.

Short tau inversion recovery (STIR) also suppresses fat, which has a short T1 relaxation time. Other tissues with short T1 relaxation (haemorrhage, metastases and melanoma) are also suppressed.

Diffusion weighted imaging

This very rapidly acquired sequence forms an image based on the microscopic motion of water molecules and may potentially help to detect extra liver lesions and help better characterize them in conjunction with other sequences.

Contrast-enhanced magnetic resonance liver imaging

Gadolinium-enhanced T1-weighted MRI

These probably do not increase sensitivity for focal abnormalities but may help in tissue characterization. When used in conjunction with spoiled GRE sequences it is possible to obtain images during the arterial phase (ideal for metastatic disease and hepatocellular carcinoma), portal phase (hypovascular malignancies) and equilibrium phase (cholangiocarcinoma, slow-flow haemangiomas and fibrosis). Hepatic arterial phase and fast spin-echo T2-weighted sequences are the most sensitive sequences for the detection of hepatic metastases of neuroendocrine tumours.

Liver-specific contrast agents

Standard gadolinium extracellular agents are commonly used for liver MRI as described above, but other contrast agents have been developed to enhance the distinction between normal liver and lesions, especially malignant lesions. These are mostly used in patients who are potentially suitable for major liver surgery, e.g. resection or transplantation:

1.
Hepato-biliary agents (e.g. Gadoxetic acid (Primovist®); gadobenate dimeglumine (Multihance®)) are taken up by normal hepatocytes and excreted by normal liver into the bile. The normal liver shows increased signal on T1-weighted sequences for a prolonged period which varies according to the particular agent. Metastases, and other lesions not containing normal-functioning hepatocytes, show as a lower signal than the background liver. Lesions containing hepatocytes will enhance to varying extents. High signal contrast can be seen in the bile ducts which has clinical usefulness. These agents are also excreted by the kidneys. Further details cany be found in Chapter 2 .
2.
Reticuloendothelial (RE) cell agents (also called super paramagnetic iron oxides, SPIO) are not currently available as they have been withdrawn from the market for commercial reasons. They are taken up by the RE or Kuppfer cells in normal liver giving a decrease in signal on T2- and especially T2*-weighted sequences. They can also be used with T1-weighted sequences for characterization. On T2*-weighted images, malignant lesions without RE cells show as higher signal than the background normal liver. Examination with a SPIO agent may be combined with dynamic gadolinium enhancement in order to maximize the detection and characterization of metastases (and benign lesions) in a patient being considered for surgical resection of metastases. The same combination can be used in a patient with cirrhosis to maximize diagnosis and characterization of HCC vs dysplastic or regenerative nodules.

Magnetic resonance angiography

Contrast-enhanced spoiled GRE images may be obtained to give information with respect to the hepatic artery, portal vein and hepatic venous system.

Magnetic resonance cholangiopancreatography (MRCP)

Indications

1.
Investigation of obstructive jaundice
2.
Suspected biliary colic/bile duct stones
3.
Suspected chronic pancreatitis
4.
Suspected sclerosing cholangitis
5.
Investigation of jaundice or cholangitis in patients who have undergone biliary enteric anastomosis
6.
Prior to ERCP/PTC.

Contraindications

Those that apply to MRI – see Chapter 1 .

Technique

MRCP is a non-invasive technique which uses heavily T2-weighted images to demonstrate the intra- and extrahepatic biliary tree and pancreatic duct. Most commonly used to demonstrate the presence of stones and the level and cause of obstruction, especially combined with cross-sectional MRI, in cases of tumour or suspected tumour.

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Methods of imaging the hepatobiliary system

Methods of imaging the pancreas

Plain films

Ultrasound of the liver

Indications

Contraindications

Patient preparation

Equipment

Technique

Additional views

Hepatic veins

Portal vein

Hepatic artery

Common bile duct

Spleen

References

Further Reading

Ultrasound of the gallbladder and biliary system

Indications

Contraindications

Patient preparation

Equipment

Technique

Additional views

Assessment of gallbladder function

Intrahepatic bile ducts

Extrahepatic bile ducts

Post-cholecystectomy

Further Reading

Ultrasound of the pancreas

Indications

Contraindications

Patient preparation

Equipment

Technique

Further Reading

Computed tomography of the liver and biliary tree

Indications

Contraindications

Technique

Single-phase (portal phase) contrast-enhanced CT

Multiphasic contrast-enhanced CT

Computed tomographic cholangiography

Contraindications

Indications

Technique

References

Further Reading

Computed tomography of the pancreas

Indications

Contraindications

Technique

Further Reading

Magnetic resonance imaging of the liver

Indications

Magnetic resonance imaging pulse sequences

Diffusion weighted imaging

Contrast-enhanced magnetic resonance liver imaging

Gadolinium-enhanced T1-weighted MRI

Liver-specific contrast agents

Magnetic resonance angiography

Magnetic resonance cholangiopancreatography (MRCP)

Indications

Contraindications

Technique

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