• Substantial cost saving on film and processing chemicals

• Reduced physical space needed for storage

• Reduced staff costs—no need to file or retrieve films

• Better availability of images—no need to obtain physical films; several viewers can see the same images simultaneously in their place of work

• Substantially reduced numbers of missing examinations

• Easy transmission of images from one institution to another—by portable storage media (CD-ROM) or electronic links

Chest X-ray: Interpreting plain chest X-rays requires a methodical approach. Several learned documents have been written on the subject (see e.g. http://student.bmj.com/student/view-article.html?id=sbmj04018), and no attempt will be made to produce an incomplete version here.

Plain abdominal radiology: Most abdominal films are taken with the patient supine. Bowel is visible when it contains gas (Figs 5.3 and 5.4); normal small bowel is less than 3 cm wide and tends to occupy the centre of the abdomen. When dilated, it shows transverse folds (plicae circulares) which completely cross the lumen. The colon usually lies peripherally and has haustrations; these folds only partly traverse the lumen (Fig. 5.3). Normal colon is less than 6 cm wide and often contains faecal lumps with a mottled appearance. Further reading about this topic is available from: http://www.studentbmj.com/topics/clinical/imaging_techniques.php.

The kidneys may be outlined by a border of perinephric fat but outlines are often obscured by bowel gas and faeces. After nephrectomy, the ‘renal outline’ may persist and the kidney appears to be present. Small urinary tract stones are easily obscured and the liver may be visible but its size cannot be estimated.

When examining an abdominal X-ray, important features to look for are:

The limitations of plain abdominal radiography are summarised in Box 5.1.

Bone X-rays: Conventional radiographs of bones continue to play an important role in diagnosis of bone disease, particularly fractures, but also infection, neoplasia and degenerative conditions. Other investigations including bone scintigraphy, CT, MRI and ultrasound are often used, particularly if conventional X-rays are normal. If in doubt it is best to discuss with a radiologist.

Contrast materials: Barium sulphate is the best agent for directly outlining the GI tract. It is insoluble in water and is not absorbed. An aqueous suspension is non-irritant and very radiodense. Barium investigations of the upper and lower gastrointestinal tracts have been largely superseded by endoscopy or cross-sectional imaging but are still occasionally employed.

Water-soluble iodinated benzoic acid derivatives can be injected into arteries or veins to opacify them (arteriography or venography). Injectable contrast media have improved over the years to make them safer but they remain potentially nephrotoxic in patients with renal impairment.

Direct venography has largely been replaced by colour duplex ultrasound, and CT or MR angiography is used more than direct studies for diagnosis.

Examples of contrast radiology:

Complications of barium contrast studies: The limitations of barium contrast studies are summarised in Box 5.2. There is a risk that contrast material may be aspirated into the bronchial tree, causing aspiration pneumonitis, so care must be taken when giving oral barium to patients with swallowing difficulties. CT scanning is safer and more likely to provide useful information such as the level and cause of obstruction, and associated pathology such as lung or liver metastases.

Magnetic resonance cholangio-pancreatography (MRCP) (Fig. 5.6 e and f): MRCP now produces images that rival the quality of ERCP. MRI differentiates tissues and organs by their varying water content. Bile and pancreatic juice are mostly water, hence MRCP gives clear images of bile in the gall bladder and ducts and outlines the pancreatic duct. It reveals filling defects caused by stones or tumours. MRCP can identify bile leaks, gallstones in the bile ducts, and duct obstruction from any cause. There are no known hazards. MRCP is increasingly used prior to ERCP for pancreatico-biliary investigation to reduce the number of patients requiring the more invasive investigation.

Indications for MRCP include:

Percutaneous transhepatic cholangiography (PTC): Percutaneous cholangiography is rarely used for diagnosis but has occasional therapeutic indications. A long fine (22 G) ‘Chiba’ needle is passed percutaneously, directly into dilated intrahepatic ducts, and contrast injected to display the duct system (see Fig. 5.6c). This shows the configuration of extrahepatic duct obstruction from the proximal direction. Occasionally, PTC is employed to drain obstructed ducts after failed endoscopic placement of a drain or stent. In jaundiced patients, disordered blood clotting is likely so a clotting screen and platelet count should be performed before PTC, and any clotting disorder corrected.

Endoscopic retrograde cholangio-pancreatography (ERCP): This is described below (see Diagnostic and therapeutic duodenoscopy); its use in obstructive jaundice is described in detail in Chapter 18. The basic technique is illustrated in Figure 5.6 a and b.

Operative cholangiography and choledochoscopy: It is standard practice to perform operative cholangiography during open cholecystectomy. For laparoscopic cholecystectomy, some surgeons routinely perform operative cholangiography whilst others prefer no imaging at all for selected cases or else preoperative assessment using MRCP for cases deemed likely to have duct stones.

Operative cholangiography allows the (highly variable) biliary anatomy to be displayed, it demonstrates stones in the bile ducts and it shows whether contrast flows freely into the duodenum. A fine plastic cannula is introduced into a small cystic duct incision and passed into the common bile duct. Water-soluble contrast material is injected to outline the duct system and fluoroscopic images or X-ray films are taken. If duct stones are demonstrated, they are often retrieved surgically at the same operation. At open cholecystectomy, this is via a longitudinal incision in the common bile duct (exploration of the common bile duct). At laparoscopic surgery, the same technique is used with a small transverse or longitudinal choledochotomy, depending on the duct size and the stone size to be retrieved. A flexible 5 mm or 3 mm endoscope called a choledochoscope is passed into the bile duct and stones may be retrieved using a range of techniques including snares, baskets, balloons, or they can even be shattered with lithotripsy probes. The choledochoscope enables the bile and intrahepatic ducts to be inspected afterwards to see that all stones have been removed. A further cholangiogram is often done afterwards to ensure the duct is clear. Stone removal may be deferred and performed later at ERCP although it carries risk of complications, including biliary leakage and acute pancreatitis.

T-tube cholangiography: Following exploration of bile ducts for stones, a T-tube is often left in situ to drain the duct. The transverse limb of the T lies in the duct and the long limb drains out through an opening in the duct to the skin where it is connected to a drainage bag. About 1 week after operation, contrast can be injected along the T-tube to outline the biliary tree and show abnormalities such as residual stones, bile leakage and duct stenoses as well as confirming free drainage into the duodenum. If residual stones are still present they can be retrieved either at ERCP or sometimes by the radiologists via the T-tube itself.

Percutaneous transluminal angioplasty (PTA) or balloon angioplasty: