The main aim of these investigations is to delineate the anatomy and to look for any abnormality in the liver or biliary tree.
Plain X-rays of the abdomen
These are rarely requested but may show:
GALLSTONES -10% contain enough calcium to be seen
AIR IN THE BILIARY TREE owing to its recent instrumentation, surgery or to a fistula between the intestine and the gallbladder
CALCIFICATION OF THE GALLBLADDER (porcelain gallbladder) – rare
This is a non-invasive, safe and relatively cheap technique. It involves the analysis of the reflected ultrasound beam detected by a probe moved across the abdomen. The normal liver appears as a relatively homogeneous structure. The gallbladder, common bile duct, pancreas, portal vein and other structures in the abdomen can be visualized.
It is useful in:
• A jaundiced patient
• The detection of gallstones
• Focal liver disease -lesions >1 cm
• General parenchymal liver disease
• Assessing portal and hepatic vein patency
• Lymph node enlargement
Other abdominal masses can be delineated and biopsies can be obtained under ultrasonic control. Doppler ultrasound can show the direction of blood flow in the portal and hepatic veins.
Computed tomography (CT) examination
This is useful in all hepatobiliary problems and is complementary to ultrasound. Pancreatic disease, enlargement of regional lymph nodes, and lesions in the porta hepatis can be visualized. Abnormalities of size, shape and density as well as focal lesions of the liver can be detected. CT can detect calcification not seen on plain X-rays. It is not as useful as ultrasound for biliary tract disease but has advantages in obese subjects. As with ultrasound, biopsies
can be taken under CT control.
Magnetic resonance imaging (MRI)
In this technique, the amplitude of an MR signal depends on proton density, Tl, T2 and flow. The higher the proton density of the tissue being imaged, the greater the signal obtained and thus the tissue will appear brighter on the image. Tl and T2 are relaxation time constants for the magnetism to return to equilibrium and these properties are intrinsic to different tissues, e.g. fat or muscle. The normal Tl and T2 can be altered by disease, for example, a focal hepatic mass such as a cyst will have aprolonged Tl and T2 relaxation.
MRI is useful in the detection and characterization of focal hepatic lesions (Fig. 5.6), diffuse parenchymal disease and hepatic and venous blood flow alteration. Its usefulness compared to CT scanning is still being evaluated.