Imaging and Interventional Techniques in Radiology and Surgery

Radiation Safety

Ionising radiation is both mutagenic and carcinogenic and irradiation of patients and observers must be minimised. This is achieved by:

• Giving training in radiation protection to all staff using and working near x-ray equipment.

• Ensuring every investigation potentially helps with management and none is performed merely as ‘routine’.

• Improving design of x-ray equipment to minimise radiation dose and scatter whilst preserving diagnostic detail.

• Low energy radiation which would be absorbed by the body is removed by thin copper or aluminium filters. This radiation would cause harm and not contribute to formation of the image.

• Physical barriers are built into radiology suites or provided to protect staff. These include barium plaster in walls, lead-glass windows and lead-rubber aprons.

• Workers involved with x-rays should keep away from the direct beam line and maintain a good distance from the x-ray source during exposure. Note that the inverse square law determines the fall-off of radiation with distance.

• All involved in radiography should be monitored and wear x-ray-sensitive film badges which need to be regularly assessed for excess radiation exposure.

Contrast Media Safety

• 1.

  Iodinated contrast —intravenous iodinated contrast can occasionally cause hypersensitivity reactions and rarely anaphylaxis. It is also potentially nephrotoxic in patients with impaired renal function. Risk factors should be specified in requests to help the radiologist plan the safest investigation. Alternatives, such as ultrasound, unenhanced CT or magnetic resonance (MR) may be considered.

  • Important risk factors for hypersensitivity are:

  • known previous reaction to iodinated contrast

  • history of asthma

  • previous significant allergic reactions or eczema

  • Risk factors for nephrotoxicity:

  • diabetes mellitus

  • renal insufficiency (include results of renal function tests in requests for CT). Patients with estimated glomerular filtration rates (EGFR) greater than 45 mL/min/1.73 m ² —do not require any precautions. EGFR 30 to 45 mL/min/1.73 m ² —consider precontrast hydration with intravenous normal saline. EGFR less than 30 mL/min/1.73 m ² —give precontrast hydration. Contrast can be given if the patient is on dialysis or is planned to have dialysis.

  • multiple myeloma

  • heart failure

Further information can be obtained at:

https://www.ranzcr.com/college/document-library/ranzcr-iodinated-contrast-guidelines

• 2.

  Gadolinium chelates —gadolinium compounds used for intravenous contrast enhancement for magnetic resonance imaging (MRI) can cause allergic reactions, although the risk is lower than with iodinated contrast. The main risk is of inducing nephrogenic systemic sclerosis (a fibrotic skin disorder) in patients with impaired renal function. Particular compounds are less risky than others and should be used if enhancement is essential in a patient with renal impairment.

Magnetic Resonance Imaging Safety

MRI is safer than ionising radiation. It is generally thought to be safe in pregnancy, but should not be undertaken without careful consideration. The main MR safety problems relate to the effect of powerful magnets upon ferromagnetic objects, both extraneous and within the patient.

• Ferromagnetic objects are excluded from the scanning room because the powerful magnetic field can propel them with such great speed that they become missiles, liable to cause physical injury.

• The magnetic field acts upon implanted metal including embedded foreign bodies and surgical clips. Metallic foreign bodies in the eye can become displaced and result in blindness. Similarly, clips on cerebral aneurysms can become dislodged. Most modern aneurysm clips are nonferromagnetic and unaffected by MRI but should still be fully documented in the patient’s notes.

• The nature of any implanted medical devices must be known. Cardiac pacemakers and external defibrillators may malfunction when exposed to the magnetic field so alternative imaging should be used. Implanted metal may also become heated by induced electrical currents.

• Firmly implanted prosthesis, such as hip replacements made of ‘MRI friendly’ materials generally safe.

Image Storage and Transfer

Virtually all images are now stored electronically in digital format and are viewed and interpreted from screens attached to computers. Images no longer need to be kept in bulky packets and space has been saved. The time and effort for staff retrieving and filing packets is now no longer needed. Of course, the systems to store the data need to be maintained and kept free from viruses and malware intrusion and so IT input is required to maintain hardware and software to keep abreast of technological changes.

Images can be viewed from multiple sites in the same institution at the same time. They can also be transferred with ease over networks to other institutions, the clinician’s home or even to other parts of the world for interpretation. Adherence to strict data security principles is mandatory. In the European Union, this is defined by the General Data Protection Regulations (GDPR).

Plain Radiology

Plain radiographs of the chest and abdomen are now used much less in surgical practice. Their limitations are better recognised and there is increased availability of CT. Studies have shown that CT is far more accurate in diagnosing a wide range of acute abdominal conditions, so it is used more often and earlier in the diagnostic pathway than previously. In cases of suspected perforation or bowel obstruction, plain radiographs of chest and abdomen are often still used as the first imaging test. Plain abdominal radiographs are also useful to monitor colonic dilatation in patients with colitis. In the nonemergency state, they are also useful to follow up renal tract calculi for size, number and position.

Abdominal Radiograph

Interpretation of abdominal radiographs demands a systematic approach. It is helpful to consider the organs in and around the abdominal cavity methodically, both intraperitoneal and retroperitoneal, the lung bases, bones and the hernial orifices. The following site should be informative as a starter: https://geekymedics.com/abdominal-x-ray-interpretation/ .

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

• calcification in areas prone to stone formation (e.g., kidney, ureters, bladder or biliary tree);

• dilated bowel (stomach, small or large bowel);

• free intraperitoneal gas indicating bowel perforation;

• gas in abnormal places (e.g., biliary tree or urinary tract) suggesting a fistula with bowel);

• nonbiological objects (e.g., foreign bodies, surgical tubes or pieces of metal);

• pathological calcification (e.g., aortic aneurysm, pancreas, adrenals or uterine fibroids).

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 (see Fig. 5.3 ). Normal colon is less than 6 cm wide and often contains faecal lumps with a mottled appearance.

The limitations of plain abdominal radiography are summarised in Box 5.1

BOX 5.1

Limitations of Plain Abdominal Radiography

• Intraperitoneal structures are not visualised unless they contain gas themselves, displace gas-filled bowel or indent structural fat.

• Stones that are not calcified (90% of gallstones, 10% of urinary tract stones) are not visible.

• Bowel gas and faeces easily obscure stones.

• Phleboliths, calcified abdominal lymph nodes and costal cartilages readily mimic stones.

• Liver and spleen size cannot be estimated accurately.

• Free intraperitoneal gas is not usually visible on a supine film (a horizontal beam film is needed).

Free Intraperitoneal Gas

Free gas is diagnostic of bowel perforation except after recent laparotomy. Free air usually persists for 3 to 6 days after laparotomy, although can remain for longer. This can cause difficulty in diagnosing a possible anastomotic leak. Carbon dioxide gas used in laparoscopic surgery is usually absorbed more quickly than air.

An erect chest radiograph is the best technique for demonstrating free air from a perforation (see Fig. 19.8 , p. 302). Perforation can also be diagnosed when both the inside and outside of bowel wall are outlined by radiolucent shadows. This is known as Rigler’s sign , Fig. 32.7 , p. 437). CT should be requested where the clinical diagnosis is not obvious or the plain x-ray result is doubtful or the patient too ill to sit or stand, or if perforation is clinically suspected but plain radiography does not show free air (see Fig. 5.4 ).

Bone Radiographs

Conventional radiographs of bones still have an important role in diagnosis of bone disease: fractures, infection, neoplasia and degenerative conditions. Other investigations including bone scintigraphy, CT, MRI and ultrasound are used when either radiographs are normal, or for further evaluation of radiographically demonstrated abnormalities. If in doubt, discuss with a radiologist.

Contrast Materials

Barium sulphate is very dense and useful for outlining the gastrointestinal (GI) tract directly, unless a leak or perforation is suspected or there is a risk of aspirating into the lungs. In these cases, a water soluble iodinated compound should be used (see Box 5.2 ).

Iodinated benzoic acid derivatives are water soluble compounds that can be injected into arteries or veins to opacify them. Contrast enhancement of CT scans is a development

Case History

that can provide useful extra information. For example, imaging arterial stenoses or venous thromboses effectively using lower doses of contrast, and thus replacing direct studies. Enhanced CT can increase the visibility of liver metastases compared to unenhanced CT.

Gadolinium chelates —are ferromagnetic compounds injected to enhance tissues during MRI examinations. They are analogous to the iodinated contrast agents used with CT and can increase the visibility of lesions and provide information about arteries and veins.

Ultrasound contrast agents —consist of a micro air bubble within a shell. The air bubble reflects sound waves and so the contrast agent shows up brightly in the examination. Contrast enhanced ultrasound is mainly used in evaluating liver lesions, differentiating benign from malignant lesions by virtue of their differing vascular characteristics. Secondly, these agents are useful for increasing the clarity of a vessel or cardiac chambers and determining the presence or absence of clots or occlusions.

Examples of Contrast Radiology

Large Bowel

With improved technology, CT has almost completely replaced the barium enema. It can be performed without laxative preparation in cases where it would be acceptable to miss small polyps. CT can be particularly useful in the frail elderly when a right-sided colonic cancer is suspected because of anaemia or a palpable mass.

In cases where it is important to detect polyps as well as larger cancers, CT colonography (CTC) is requested. This test involves bowel cleansing to eliminate particulate matter. During the procedure, air or carbon dioxide is insufflated into the colon and the technique is sensitive enough to detect lesions of 1 cm or even smaller. With good technique, the accuracy of CTC is equivalent to optical colonoscopy in detecting polyps and cancers ( Fig. 5.5 ).

Small Bowel

The use of barium studies to examine small bowel is declining and being replaced by CT or MR enterography. These techniques also enable the attached mesentery to be examined for complications, such as abscesses or fistulae. Capsule endoscopy can be used to look for small lesions that remain undetected by other tests (see later).

Magnetic Resonance Cholangio-Pancreatography ( Fig. 5.6C and D )

Magnetic resonance cholangio-pancreatography (MRCP) now produces images that rival the quality of endoscopic retrograde cholangio-pancreatography (ERCP). MRI differentiates tissues and organs by their varying water content. Since 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 bile ducts, and duct obstruction from any cause. There are no known hazards. MRCP is increasingly used ahead of ERCP for pancreatico-biliary investigation to reduce the number of more invasive (and potentially risky) investigations.

Indications for MRCP include:

• Suspected stones in the biliary tree.

• Bile duct strictures: benign—postsurgical or sclerosing cholangitis; malignant—cholangiocarcinoma.

• Congenital ductal anomalies: pancreas divisum causing acute pancreatitis of unknown aetiology. Choledochal cysts.

• Biliary-type pain with abnormal liver function tests in patients without stones on ultrasound.

• Patients unsuitable for ERCP because of intolerance or have had previous gastrectomy.

Endoscopic Retrograde Cholangio-Pancreatography

This is described subsequently (see Diagnostic and therapeutic duodenoscopy ); its use in obstructive jaundice is described in detail in Chapter 18 . The basic technique is illustrated in Fig. 5.6A and B .

General Principles and Hazards of Arteriography and Venography

Further detail about applications of vascular radiology is given in Chapter 41 .

The veins or arteries of an anatomical region can be opacified by intravenous or intraarterial injection of contrast medium. This is angiography and includes arteriography and venography. In arteriography , needle puncture of the access artery is followed by guide-wire insertion, needle removal and catheter insertion over the guide-wire. Shaped catheters and wires are used to advance the catheter tip to an appropriate position for arteriography. Favoured access sites are the femoral artery in the groin, the brachial artery at the level of the elbow and, more recently, the radial artery at the wrist, using smaller diameter sheaths.

Clotting studies should be performed beforehand to anticipate potential haemorrhagic complications from the vessel puncture site, particularly if the patient is on anticoagulants or if there is a suspicion of an underlying clotting disorder.

The contrast medium is the same as that used for CT and carries similar hazards, that is, allergic reaction and nephrotoxicity (see earlier).

Complications from the vascular access site include bleeding or thrombosis in veins and dissection, arteriovenous fistula or pseudoaneurysm formation in arteries.

Endovascular Techniques

Percutaneous Transluminal Angioplasty or Balloon Angioplasty

Angioplasty under local anaesthesia is a less invasive alternative to surgery for treating many peripheral and coronary arterial stenoses. In general, short stenoses in large vessels are most suitable. The method is particularly useful for atherosclerotic disease involving the lower limbs, coronaries and abdominal visceral arteries (coeliac, SMA and renal arteries). Carotid artery disease is also suitable for angioplasty in some cases; filters or embolic protection devices are usually placed above the stenotic segment before dilatation to reduce the risk of distal embolisation to the brain.

Major complications of angioplasty are rare in experienced hands but there is a small risk of precipitating acute ischaemia because of distal embolisation or dissection. Thus surgical salvage should be readily available should complications develop. Unfortunately, 25% to 40% of angioplastied lesions undergo restenosis or occlusion within 1 year, but the process can usually be repeated. Where stenoses fail to remain open at plain balloon angioplasty, stents can be placed across the treated lesion to provide a sustained outward radial force, thereby keeping the vessel patent. Advances incorporate certain drugs (with antiproliferative properties) into balloons and stents to reduce rates of restenosis and improve long-term patency. These stents are mounted on an angioplasty balloon before deployment or are self-expanding once deployed in the vessel. Stents are increasingly used in iliac, superficial femoral artery and popliteal stenoses and occlusions. Overall, angioplasty causes minimal interventional and anaesthetic stress to the patient and is often performed on a day-case basis.

Techniques of Percutaneous Angioplasty

Angioplasty is usually performed under local anaesthesia ( Fig. 5.7 ). A needle is first inserted into an accessible artery and a short flexible guide-wire passed through it into the artery and the needle removed. A working sheath with a valved side-arm is passed over the guide-wire and advanced into the artery. A catheter is inserted and a long guide-wire is then substituted for the first and manipulated up to and through the stenosis guided by contrast injections and fluoroscopic control. An angioplasty catheter with a plastic inflatable balloon at its end is then passed over the guide-wire and manipulated across the stenosis. Angioplasty balloons are now no wider than the catheter before inflation, and designed to inflate to a fixed diameter at a given pressure. It is possible to measure the arterial pressure above and below the stenosis to determine the pressure gradient before and after angioplasty, and although not performed routinely, it can provide an objective measure of the physiological response to treatment. The balloon is inflated to a typical pressure of between 6 and 15 atmospheres depending on the balloon type, to dilate the stenosis, then further contrast is injected to check the result. Angioplasty techniques and equipment have progressively improved and many patients now return to near-normal life after minimal intervention. Many patients with ischaemic legs or coronary heart disease who might not have been suitable for reconstructive surgery can now have angioplasty because of its minimally invasive nature and low complication rates.

Local Arterial Thrombolytic Therapy

An artery freshly occluded by thrombus and causing ischaemia can be recanalised by local intraarterial infusion of thrombolytic agents. High local concentrations with limited systemic spill-over were intended to avoid the serious bleeding and allergic complications of systemic thrombolysis. However, experience has shown that the risk of major haemorrhage still exists, with some episodes having been fatal. Examples of serious complications include intracerebral haemorrhagic strokes, bleeding from recent surgical wounds, from the GI tract or intraocular bleeding in patients with untreated proliferative diabetic retinopathy. For this reason, the treatment has strictly limited indications, that is, recently occluded native arteries or bypass grafts. The thrombolytic agent usually used is recombinant tissue plasminogen activator (R-tPa). R-tPa acts more quickly and does not have the frequent allergic effects of older agents, for example, streptokinase.

For recent acute embolic ischaemia, surgical embolectomy remains the best treatment.

Therapeutic Embolisation

Highly vascular lesions or vessels that are actively bleeding that would be difficult or impossible to treat by surgery alone can have their arterial supply reduced or obliterated by embolisation. The main supplying artery is identified by selective arteriography and a catheter manoeuvred into it, close to the lesion. The materials chosen for embolisation depend on the nature of the lesion but include gelatine foam , polyvinyl alcohol particles , minute steel coils , plugs , cyanoacrylate glue or liquid polymers . The process can be repeated for all the feeding vessels.

Embolisation is particularly useful in the treatment of GI haemorrhage, some pseudoaneurysms, uterine fibroids and internal iliac arteries before endovascular aneurysm repair (EVAR). The technique is also used to treat hepatic tumours (primary and secondary) and some bone metastases before surgery.

Minimal Access Graft Placement

EVAR is now widely used to treat both abdominal and thoracic aortic aneurysms. There are several different types of device available, all composed of metal stents and graft material, and technical improvements are continuing. The device is introduced via a femoral artery and accurately positioned in the aorta, and then deployment consists of unsheathing the device under fluoroscopic guidance. Graft limbs are added to extend the device into the iliac arteries. There are now stent grafts capable of treating more complex aneurysms with side branches/grafts into renal, mesenteric, internal iliac or aortic arch arteries. These techniques create a better seal for the aortic stent graft without compromising flow to the visceral arteries. One disadvantage of EVAR includes endoleakage , that is, continued slow bleeding into the aneurysm sac because of an inadequate seal or, more commonly, from lumbar arteries or the inferior mesenteric artery. Other complications include graft migration, limb occlusion or limb dislocation. Although reintervention rates are higher than with open aneurysm repair, these techniques have allowed many patients to be treated who would never be fit for open surgery. There is now an increasing application of EVAR to leaking or ruptured aneurysms. This avoids the massive physiological insult associated with open surgery. The late complication rate of EVAR is about 10% per year, considerably greater than for open aneurysm grafting, but rates are falling with improving techniques.